| Picture | Title | Caption | Copyright |
|---|---|---|---|
| Larval dust | Dust created by larval boring in bark crevice indicating attack by T. piniperda. | ©Bo Långström | |
| Early gallery | Early gallery with male and female of T. piniperda. | ©Bo Långström | |
| Fully developed egg galleries | Fully developed egg galleries with resin-soaked edges. | ©Bo Långström | |
| Exit holes in bark | Adult exit holes in bark indicating successful brood production. | ©Bo Långström | |
| Resin flow on bark | Resin flow on bark of standing pine indicating failed attack. | ©Bo Långström | |
| Reaction zones | Reaction zones surrounding failed egg gallery under bark. | ©Bo Långström | |
| Blue-stained timber | Blue-stain and egg galleries of T. piniperda. | ©Bo Långström | |
| Resin tube | Resin tube signalling shoot attack in early season by Tomicus sp. | ©Bo Långström | |
| Dissected pine shoot | Shoot opened to display pine shoot beetle in feeding tunnel. | ©Bo Långström | |
| Fallen pine shoots | Fallen pine shoots on the ground beneath tree indicate feeding by pine shoot beetles. | ©Bo Långström | |
| Damaged pine stand | Pine stand damaged over 3 years by pine shoot beetles. | ©Bo Långström |
Datasheet
Tomicus piniperda (common pine shoot beetle)
Index
- Pictures
- Identity
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Description
- Distribution
- Distribution Table
- Habitat
- Hosts/Species Affected
- Host Plants and Other Plants Affected
- List of Symptoms/Signs
- Biology and Ecology
- Natural enemies
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Plant Trade
- Wood Packaging
- Impact
- Environmental Impact
- Detection and Inspection
- Similarities to Other Species/Conditions
- Prevention and Control
- References
- Distribution Maps
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Top of pageIdentity
Top of pagePreferred Scientific Name
- Tomicus piniperda (Linnaeus, 1758)
Preferred Common Name
- common pine shoot beetle
Other Scientific Names
- Blastophagus destruens (Wollaston, 1865)
- Blastophagus major Eggers, 1943
- Blastophagus piniperda (Linnaeus, 1758)
- Bostrichus abietinus Fabricius, 1792
- Bostrichus testaceus Fabricius, 1787
- Dermestes piniperda Linnaeus 1758
- Hylesinus piniperda (Linnaeus, 1758)
- Hylurgops piniperda (Linnaeus, 1758)
- Hylurgus analogus Le Conte, 1868
- Hylurgus destruens Wollaston, 1865
- Myelophilus piniperda (Linnaeus, 1758)
- Myelophilus piniperda rubescens Krausse
- Myelophilus piniperda rubripennis Reitter
- Myelophilus testaceus (Fabricius, 1787)
- Tomicus destruens (Wollaston, 1865)
- Tomicus piniperda Latreille 1802
- Tomicus piniperda rubescens Krausse
International Common Names
- English: beetle, pine; beetle, pine shoot; Japanese pine engraver; larger pith borer; pine beetle; pine engraver, Japanese; pine shoot beetle; pith borer, larger
- Spanish: hilesino destructor de los pinos; jardinero del monte
- French: blastophage destructeur du pin; hylesine du pin; jardinier des bois
- Portuguese: hilésina do pinheiro
Local Common Names
- Denmark: marvborer; marvborer, fyrrens
- Finland: pystynävertäjä
- Germany: Grosser Waldgärtner; Kaefer, Grosser Kiefernmark-; Waldgärtner, Gefurchter; Waldgärtner, Grosser
- Italy: mielofilo distruttore dei pini
- Japan: matu-no-kikuimusi
- Netherlands: dennenscheerder
- Norway: den store margboreren
- Sweden: större märgborre
EPPO code
- BLASPI (Tomicus piniperda)
Summary of Invasiveness
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T. piniperda is classified as an invasive species after its introduction to North America, where it is currently spreading.
Taxonomic Tree
Top of page- Domain: Eukaryota
- Kingdom: Metazoa
- Phylum: Arthropoda
- Subphylum: Uniramia
- Class: Insecta
- Order: Coleoptera
- Family: Scolytidae
- Genus: Tomicus
- Species: Tomicus piniperda
Notes on Taxonomy and Nomenclature
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Tomicus piniperda was described by Linnaeus in 1758 as Dermestes piniperda. In 1802, Latreille established the genus Tomicus with the Type species T. piniperda. In 1864, Eichhoff moved the species to the new genus Blastophagus, and in 1878 created the new genus Myelophilus. In the 1970s, the genus Tomicus was re-established, and is now the valid generic name. Pfeffer (1994) lists several older synonyms for the species. The specific status of T. piniperda in Yunnan, China, has been questioned and there is some evidence that it is a new species (Lieutier et al., 2003); however, it is still treated as T. piniperda in other parts of the world. Tomicus destruens was described as Hylurgus destruens by Wollaston in 1865, and transferred to Blastophagus destruens by Lekander (1971). For a long time it was seen as a Mediterranean race of T. piniperda, but has recently been confirmed as a valid species (Gallego and Galian, 2001; Kerdelhue et al., 2002). Some reference will be made to T. destruens in this datasheet, but it will not be fully covered.
Description
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The egg is white, shiny and oblong, ca 1 mm long. The larva is a typical scolytid larva: a legless, whitish grub with a curved body and a brown head capsule. The mature larva is 4-5 mm long. According to Lekander (1968a, b), there are four larval instars with head capsule widths (mean ±sd) as follows: instar 1 (0.47±0.02); 2 (0.58±0.02); 3 (0.76±0.03); 4 (0.99±0.03). The pupa is white and resembles the adult insect in size and general form. The newly emerged callow adult is straw-yellow and darkens with progressive sexual maturity. The mature adult has a dark-brown head, thorax and elytra, but the latter may sometimes be reddish-brown (as in T. minor). Body length ranges from 3.5-4.7 mm in Sweden (Spessivtseff, 1922) to 3.5-4.8 mm in Germany (Postner, 1974). On average, T. piniperda is larger than T. minor. The best character to distinguish between the adults of the two species is the presence of setae in all setal rows on the elytra in T. piniperda and the lack of setae in the second row on the beetle declivity in T. minor (Ritchie, 1917; Spessivtseff, 1922). T. piniperda is difficult to separate from T. destruens but, according to Lekander (1971) and Pfeffer (1994), T. destruens should have more yellow antennal clubs than T. piniperda. Faccoli (2006) provides further details on separating T. piniperda and T. destruens using morphological characters. Kohlmayr et al. (2002) state that the best key to identification is that T. destruens has three rows of hairs on the second antennal segment, whereas T. piniperda has only one row. Males and females can be separated by the shape of the last abdominal tergite, which is small and square-shaped in the male and larger and semi-circular in the female (Salonen et al., 1968). Live beetles of both species can also be sexed by the audible stridulation of males when held close to the ear (Schönherr, 1970; Salonen, 1973).
Distribution
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T. piniperda has an extremely wide geographical distribution, extending from Portugal in the west to Japan in the east, and from the timberline beyond the arctic circle in the north to northern Africa in the south (Browne, 1968; Lekander et al., 1977). In 1992, T. piniperda was found in Ohio, USA, and several other states surrounding the Great Lakes; in the following year it was recorded in Ontario, Canada; and by the year 2000 it had been recorded from 12 states in USA and two provinces in Canada (Haach and Poland, 2001). However, later damage surveys indicated that T. piniperda must have been present long before detection, at least in New York State, USA, and Ontario, Canada (Czokajlo et al., 1997; Scarr et al., 1999).
Distribution Table
Top of pageThe distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
Last updated: 17 Dec 2021| Continent/Country/Region | Distribution | Last Reported | Origin | First Reported | Invasive | Reference | Notes |
|---|---|---|---|---|---|---|---|
Africa |
|||||||
| Algeria | Present | ||||||
| Morocco | Present, Widespread | ||||||
| Tunisia | Present, Widespread | Original citation: Ben Jamaa et al., 2000 | |||||
Asia |
|||||||
| China | Present | Present based on regional distribution. | |||||
| -Jilin | Present | Original citation: Song et al. (2005) | |||||
| -Yunnan | Present, Widespread | ||||||
| -Zhejiang | Present | Original citation: Song et al. (2005) | |||||
| Georgia | Present | Original citation: Kurashvili et al. (1981) | |||||
| Hong Kong | Present | ||||||
| Israel | Present, Widespread | ||||||
| Japan | Present | ||||||
| North Korea | Present, Widespread | ||||||
| South Korea | Present | ||||||
| Turkey | Present | ||||||
Europe |
|||||||
| Austria | Present, Widespread | Original citation: Steyer et al., 2002 | |||||
| Bulgaria | Present | ||||||
| Croatia | Present, Widespread | ||||||
| Cyprus | Present | ||||||
| Czechia | Present | ||||||
| Czechoslovakia | Present, Widespread | ||||||
| Denmark | Present, Widespread | ||||||
| Estonia | Present, Widespread | ||||||
| Finland | Present, Widespread | ||||||
| France | Present, Widespread | ||||||
| -Corsica | Present | ||||||
| Germany | Present, Widespread | ||||||
| Greece | Present, Widespread | ||||||
| Hungary | Present, Widespread | ||||||
| Ireland | Present, Widespread | ||||||
| Italy | Present, Widespread | ||||||
| Latvia | Present, Widespread | ||||||
| Lithuania | Present, Widespread | ||||||
| Netherlands | Present, Widespread | ||||||
| Norway | Present, Widespread | ||||||
| Poland | Present, Widespread | ||||||
| Portugal | Present, Widespread | Original citation: Ferreira and Ferreira (1990) | |||||
| -Madeira | Present | ||||||
| Romania | Present, Widespread | ||||||
| Russia | Present | Present based on regional distribution. | |||||
| -Central Russia | Present, Widespread | ||||||
| -Southern Russia | Present, Widespread | ||||||
| -Western Siberia | Present, Widespread | ||||||
| Slovenia | Present, Widespread | ||||||
| Spain | Present, Widespread | ||||||
| Sweden | Present, Widespread | ||||||
| Switzerland | Present, Widespread | ||||||
| United Kingdom | Present, Widespread | ||||||
North America |
|||||||
| Canada | Present | Present: subject to official control. | |||||
| -Ontario | Present, Few occurrences | ||||||
| -Quebec | Present, Few occurrences | ||||||
| United States | Present | Present based on regional distribution. | |||||
| -Illinois | Present, Few occurrences | ||||||
| -Indiana | Present, Few occurrences | ||||||
| -Maine | Present, Few occurrences | ||||||
| -Maryland | Present, Few occurrences | ||||||
| -Michigan | Present, Few occurrences | ||||||
| -Missouri | Present | ||||||
| -New Hampshire | Present, Few occurrences | ||||||
| -New York | Present, Few occurrences | ||||||
| -Ohio | Present, Few occurrences | ||||||
| -Virginia | Present, Localized | ||||||
| -West Virginia | Present, Few occurrences | ||||||
| -Wisconsin | Present, Few occurrences | ||||||
Habitat
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The brood is found under the bark of fresh pine timber or in standing weakened trees. Maturation feeding of the adults takes place in the young shoots of healthy pine trees (see Detection and Inspection Methods and Biology).
Hosts/Species Affected
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T. piniperda is a common pest on many pine species throughout its geographical range. It occasionally attacks other conifers such as spruces (Picea sp.), larches (Larix sp.) and even Douglas fir (Pseudotsuga sp.) (Browne, 1968; Postner, 1974) but these cases are rare and often exceptional (Butovitsch, 1972; Löyttyniemi and Uusvaara, 1977; Lutyk, 1984). Pfeffer (1994) and Bright and Skidmore (1997) list a large number of pine species as hosts for this species.
Scots pine (Pinus sylvestris) is the principal host over much of Europe. In Sweden, T. piniperda was less attracted to lodgepole pine (Pinus contorta var. latifolia) than to P. sylvestris, but could develop in this introduced host when given no choice (Långström and Hellqvist, 1985). In southern France, T. piniperda preferred to oviposit in Pinus pinaster, but egg galleries were also recorded in Pinus halepensis, Pinus sylvestris and Pinus nigra (Lieutier et al., 1997). Amezaga (1997) reports attacks on P. sylvestris and P. radiata in Spain.
In North America, T. piniperda was first detected in a Christmas tree plantation in Ohio, USA, in 1992, and is now recorded from 12 US states and two Canadian provinces (Haack and Poland, 2001). Several studies have shown that T. piniperda can feed in the shoots of many North American pine species, both soft and hard pines (Sadof et al., 1994; Lawrence and Haack, 1995; Kauffman et al., 1998).
There is less information available regarding the suitability of American pines for oviposition, but it appears that the beetle is more selective during this phase of the life cycle. In a French-Swedish study, seven out of 10 pine species were attacked in southern France, whereas in Sweden P. sylvestris was clearly preferred over P. contorta, P. banksiana and P. strobus (Långström et al., 1995). However, in this same study, T. piniperda was shown to develop in all four species when given no choice.
Yunnan pine (Pinus yunnanensis) is the main host in southern China (Långström et al., 2002) but it was recently shown to develop in Pinus armandii, which is not normally attacked in the field (Zhao, 2003).
In conclusion, T. piniperda can live on most pine species but hard pines (diploxylon) are preferred over soft pines (haploxylon) for egg laying and brood production; the species is less discriminating during the shoot-feeding phase. Other conifers are only occasionally attacked, and cannot really be regarded as hosts.
T. destruens is reported from Pinus brutia, P. canariensis, P. halepensis and P. pinaster (Pfeffer, 1994).
Scots pine (Pinus sylvestris) is the principal host over much of Europe. In Sweden, T. piniperda was less attracted to lodgepole pine (Pinus contorta var. latifolia) than to P. sylvestris, but could develop in this introduced host when given no choice (Långström and Hellqvist, 1985). In southern France, T. piniperda preferred to oviposit in Pinus pinaster, but egg galleries were also recorded in Pinus halepensis, Pinus sylvestris and Pinus nigra (Lieutier et al., 1997). Amezaga (1997) reports attacks on P. sylvestris and P. radiata in Spain.
In North America, T. piniperda was first detected in a Christmas tree plantation in Ohio, USA, in 1992, and is now recorded from 12 US states and two Canadian provinces (Haack and Poland, 2001). Several studies have shown that T. piniperda can feed in the shoots of many North American pine species, both soft and hard pines (Sadof et al., 1994; Lawrence and Haack, 1995; Kauffman et al., 1998).
There is less information available regarding the suitability of American pines for oviposition, but it appears that the beetle is more selective during this phase of the life cycle. In a French-Swedish study, seven out of 10 pine species were attacked in southern France, whereas in Sweden P. sylvestris was clearly preferred over P. contorta, P. banksiana and P. strobus (Långström et al., 1995). However, in this same study, T. piniperda was shown to develop in all four species when given no choice.
Yunnan pine (Pinus yunnanensis) is the main host in southern China (Långström et al., 2002) but it was recently shown to develop in Pinus armandii, which is not normally attacked in the field (Zhao, 2003).
In conclusion, T. piniperda can live on most pine species but hard pines (diploxylon) are preferred over soft pines (haploxylon) for egg laying and brood production; the species is less discriminating during the shoot-feeding phase. Other conifers are only occasionally attacked, and cannot really be regarded as hosts.
T. destruens is reported from Pinus brutia, P. canariensis, P. halepensis and P. pinaster (Pfeffer, 1994).
Host Plants and Other Plants Affected
Top of pageList of Symptoms/Signs
Top of page| Sign | Life Stages | Type |
|---|---|---|
| Growing point / dieback | ||
| Growing point / internal feeding; boring | ||
| Leaves / abnormal leaf fall | ||
| Leaves / internal feeding | ||
| Stems / internal feeding | ||
| Stems / visible frass | ||
| Whole plant / internal feeding | ||
| Whole plant / plant dead; dieback |
Biology and Ecology
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A large number of studies have been devoted to the biology and ecology of T. piniperda, since the original study by Ratzeburg (1839). Escherich (1923) summarized early German work on the pest in his textbook. Since then, hundreds of papers (including dozens of doctoral dissertations and other major studies) have been published, mainly in northern parts of Europe, including Russia. Our current understanding of the life cycle and general biology of T. piniperda in Europe has evolved via basic studies in England (Hanson 1937, 1940), Finland (Kangas et al., 1971; Salonen, 1973; Saarenmaa, 1983, 1985a, b; Annila et al., 1999), France (Chararas, 1968; Sauvard, 1988; Herard and Mercadier, 1996; Lieuier, 2002), Germany (Führer and Kerck, 1978; Vité et al., 1986) Norway (Bakke, 1968) and Sweden (Långström, 1983; Byers et al., 1985; Lanne et al., 1987; Schroeder, 1988).
In eastern Europe, the focus has mainly been on the damage caused by T. piniperda in Czechoslovakia (Srot, 1968), Estonia (Voolma and Luik, 2001), Hungary (Toth, 1971), Poland (Gidaszewski, 1974; Borkowski, 2001), Romania (Drugescu, 1980; Michalciuc et al., 2001) and Russia (Agafonov and Kuklin, 1979; Bogdanova, 1988, 1998; Kolomiets and Bogdanova, 1998; Gninenko and Vetrova, 2002).
Damage reports exist from nearly all countries in southern Europe, such as Portugal (Ferreira and Ferreiera, 1990), Spain (Astiaso and Levya, 1970; Amezaga, 1996; Fernandez and Costas, 1999) southern France (Chararas, 1968), Italy (Masutti, 1969; Triggiani, 1984; Boriani, 1989), Slovenia (Jurc, 2001) and Greece (Kailides, 1964; Markalas, 1997; Avtzis and Gatzojannis, 2000). T. piniperda is also considered a major pest in Turkey (Yuksel et al., 2001), Israel (Halperin, 1978), Tunisia (Chararas, 1976; Ben Jamaa et al., 2000) and Morocco (Ghaioule et al., 1998).
In East Asia, there have been few studies on T. piniperda from Korea (Park and Lee, 1972; Park and Byun, 1988) and Japan (Masuya et al., 1998). In contrast, there are many Chinese studies, especially from Yunnan province. Much of the Chinese work on T. piniperda has until now been inaccessible to the western world, but starting with Ye (1991), an increasing number of papers are now being published in English (see Långström et al., 2002; Lieutier et al., 2003).
Dozens of North American publications have appeared on T. piniperda over the past decade (e.g. Haack and Poland, 2001; Kennedy and McCullough, 2002). Current knowledge on the biology of T. piniperda is summarized for, and compared between, Europe, southern China and North America as follows.
In northern Europe and North America, the adults of T. piniperda hibernate in short galleries in the bark at the base of standing pine trees, but elsewhere they seem to hibernate mainly in the shoots. Spring flight is the main period of dispersal and takes place in early spring when temperatures reach 12°C in the shade (flight threshold was 11°C in Saarenmaa's (1989) swarming model). This dispersal is dependent on latitude and annual variation and may occur in November-December in southern China (Li et al., 1993), January-February in the Mediterranean (Halperin, 1978), February-March in central Europe (Sauvard, 1988) and April-May in Fennoscandia (Långström, 1983). On the basis of flight and climatic data, the average peak flight of T. piniperda in North America would be February and April, at the southern and northern ends of its area of occurrence (Poland et al., 2002), corresponding to the situation in central and northern Europe.
The flying beetles respond to host odours, mainly alpha-pinene, which guide the beetles to the host material (Kangas et al., 1971; Vité et al., 1986; Byers et al., 1985; Lanne et al., 1987; Schroeder, 1988). According to Byers et al. (1989), the beetles may even recognize suitable host trees in flight. Until recently, there has been a consensus that T. piniperda lacks aggregation pheromones (Lanne et al., 1987; Löyttyniemi et al., 1988; but see also, Schönherr, 1972), but recently Poland et al. (2003) concluded that trans-verbenol may act as an aggregation pheromone in T. piniperda.
During the flight period, the females find and colonize suitable host material, i.e. fresh timber or weakened standing trees. In Europe and North America, T. piniperda mainly attacks the lower stem, which is covered with thick corky bark, whereas in China it seems to predominate on the upper part of the pine stem, which is covered with smooth bark (Långström, 1984; Ye and Ding, 1999). T. piniperda is monogamous and the female always excavates the egg gallery, which runs along the wood grain. On standing trees, the galleries are oriented upwards, but on fallen stems they may be oriented towards the base or the top. The gallery starts with a short sterile section, followed by a section with egg niches regularly spaced on both sides, and ends with another sterile section. The length of the gallery varies with attack density from 4-5 cm at high density to more than 10 cm at low density. Egg numbers can be derived from gallery lengths and densities (Saarenmaa, 1983).
T. piniperda has two main fungal associates among the blue-stain fungi: Leptographium wingfieldii and Ophiostoma minus. Only a part of the population seems to carry these fungi (Lieutier et al., 1989; Gibbs and Inman, 1991; Solheim and Långström, 1991) and their role in the biology of the beetle is not fully clarified. However, when inoculated into trees, these fungi alone can kill pine trees with reduced foliage (Solhein et al., 1993) and can grow well in the low oxygen levels of living xylem tissue (Solheim et al., 2000). Thus, they seem to play a similar role to the fungal associates of other aggressive bark beetles (such as Ips typographus) in overwhelming the resistance of live trees, but this is still under debate (cf. Lieutier, 2002).
The larvae feed on the phloem and construct winding galleries perpendicular to the egg galleries, which end in a pupal chamber in the bark or partly in the outer xylem. The pupal period is short, and the callow adults emerge via individual exit holes in the bark. In northern Europe, emergence takes place mainly during July, but varies with weather conditions. Development is faster than in Tomicus minor, and in Sweden the time from mean flight to mean emergence was recorded as 92±12 days with a thermal sum of day-degrees exceeding 0°C of 1016±79 (Långström, 1983). The immature stages do not survive the winter in Scandinavia (Bakke, 1968). In more southerly areas, emergence takes place earlier, but in these areas the occurrence of sister broods blurs the picture. This also appears to be the case in Yunnan, China (Li et al., 1993), but the time from mean flight to mean emergence ranged from 86 to 94 days in two separate laboratory studies (Chen, 2003; Zhao, 2003). In North America, the development and emergence times agreed with those for central and northern Europe. In Ontario, Canada, the thermal sum for the development period was 1250±73 day-degrees (Ryall and Smith, 2000).
There has been considerable discussion over the years about the number of generations and sister broods in pine shoot beetles per year. The statement by Ritchie (1917) that there is only one generation per year but that sister broods exist (i.e. new brood(s) by the same parent beetles in the same year) still holds for regions as different as Sweden (Långström, 1983), France (Sauvard, 1988, 1989), southern China (Långström et al., 2002) and Ontario, Canada (Ryall and Smith, 2000). In contrast, T. destruens has two overlapping generations per year in Italy (Nanni and Tiberi, 1997).
The occurrence of sister broods in T. piniperda increases from north to south. In Sweden, sister broods are rare although the thermal sum in most years would allow a sister brood in the southern part of the country (Långström, 1983). Ryall and Smith (2000) found that two broods occurred in Canada, and that the thermal sum required was lower (856 day-degrees) for the second brood. In France, Sauvard (1993) found four waves of oviposition, i.e. the initial wave and three sister broods, under semi-natural conditions. He also concluded that in France, ca 50% of the total beetle production comes from sister broods. Similarly, Srot (1968) and Lutyk (1988) have observed one or more sister broods in central Europe resulting in an extended period of beetle emergence lasting into September. The situation in China is not clear, but the occurrence of shoot-feeding beetles throughout most of the year indicates the existence of sister broods (Li et al., 1993; Långström et al., 2002).
During oviposition, the male stays in the gallery and removes the frass, but towards the end of the oviposition period, it leaves the gallery and flies to the pine crowns to feed in the shoots in order to regain sexual maturity. A few weeks later, when the females have finished oviposition in early summer, they may be found feeding in the shoots. This pattern has been seen in Sweden (Långström, 1983) and Canada (Ryall and Smith, 2000) and probably also holds true for southern China (Li et al., 1993; Långström et al., 2002).
At least in Fennoscandia, some of the adult beetles may hibernate for a second time, after a period of regeneration feeding in the shoots, and produce another brood the following year (Långström, 1983; Schroeder and Risberg, 1989). Whether this phenomenon also occurs in a warmer climate is not known, but it could well be the case considering the univoltine life cycle and the occurrence of postreproductive adults in the shoots even in southern China (Långström et al., 2002).
The main shoot-feeding period takes place when the callow adults emerge and fly to nearby pine crowns, where they tunnel mainly the current shoots at the outer parts of the branches. In Sweden, this takes place from July to October. The first severe frosts cause the beetles to leave the shoots and move to the base of standing pine trees, where they hibernate in short galleries made in the thick bark (Långström, 1983). The same pattern has been observed in North America (Kauffman et al., 1998; Ryall and Smith, 2000; Poland et al., 2002). In Yunnan, China, this period is more flexible as the life cycle is less synchronized, but the main shoot-feeding period seems to be May to November (Långström et al., 2002).
The parent beetles also move to the shoots for a regeneration-feeding period that starts earlier, and lasts longer, than that of the callow beetles. In Sweden, this regeneration feeding takes place in the previous year's shoots as the current shoots are seldom attacked while expanding (Långström, 1983). A similar pattern regarding the maturation feeding of re-emerging parent beetles has been observed in Canada (Ryall and Smith, 2000). Långström (1983) found that some beetles entered the shoots soon after the flight period and stayed there for the whole summer. As these beetles were sexually nature, he concluded that they had turned to the shoots after exhausting their fat reserves during the search for host material. There are no clear data demonstrating the presence of regeneration feeding after flight or oviposition among parent beetles in the southern parts of the distribution area of T. piniperda. It probably exists, but to what extent is not known.
In T. piniperda, shoot feeding preferentially takes place in the upper whorls of the pine crown (Führer and Kerck, 1978b; Långström, 1983; Kauffman et al., 1998). Långström (1980) concluded that the beetles colonize the crown from above, and that the outermost shoots are taken first. In Sweden, the preferred shoot diameter is ca 3-4 mm and, on average, each beetle tunnelled one shoot, although multiple attacks (same beetle in several shoots or more than one beetle in the same shoot) were not uncommon (Långström, 1980, 1983). In general, the previous year's shoots are tunnelled in early season and the current shoots in late season. This pattern in Sweden was also largely confirmed for North America (Kauffman et al., 1998; Haack et al., 2000, 2001) although, in one year, Ryall and Smith (2000) found that beetles consumed as many as five or six shoots per beetle. The shoots of Yunnan pine (Pinus yunnanensis) are generally longer and thicker, hence the mean diameter of shoot tunnelled was 7-8 mm (Ye, 1996).
There is another important behavioural difference in the Yunnan populations of T. piniperda (which may in fact be another species) in that the beetles may move directly from the shoots to the trunk (Lieutier et al., 2003). Thus, intensive shoot feeding may predispose trees to successive stem attacks, and this situation is aggravated by the fact that the beetles sometimes aggregate for shoot feeding on certain tree individuals (Ye and Lieutier, 1997). In this way, the beetles may create their own breeding materials and this may explain the hitherto unique beetle outbreak in Yunnan. Nothing similar has ever been observed, although intensive shoot feeding in a few cases has triggered stem attacks around sawmills or timber yards in England, UK (Hanson, 1937) and the USA (Czokajlo et al., 1997).
In eastern Europe, the focus has mainly been on the damage caused by T. piniperda in Czechoslovakia (Srot, 1968), Estonia (Voolma and Luik, 2001), Hungary (Toth, 1971), Poland (Gidaszewski, 1974; Borkowski, 2001), Romania (Drugescu, 1980; Michalciuc et al., 2001) and Russia (Agafonov and Kuklin, 1979; Bogdanova, 1988, 1998; Kolomiets and Bogdanova, 1998; Gninenko and Vetrova, 2002).
Damage reports exist from nearly all countries in southern Europe, such as Portugal (Ferreira and Ferreiera, 1990), Spain (Astiaso and Levya, 1970; Amezaga, 1996; Fernandez and Costas, 1999) southern France (Chararas, 1968), Italy (Masutti, 1969; Triggiani, 1984; Boriani, 1989), Slovenia (Jurc, 2001) and Greece (Kailides, 1964; Markalas, 1997; Avtzis and Gatzojannis, 2000). T. piniperda is also considered a major pest in Turkey (Yuksel et al., 2001), Israel (Halperin, 1978), Tunisia (Chararas, 1976; Ben Jamaa et al., 2000) and Morocco (Ghaioule et al., 1998).
In East Asia, there have been few studies on T. piniperda from Korea (Park and Lee, 1972; Park and Byun, 1988) and Japan (Masuya et al., 1998). In contrast, there are many Chinese studies, especially from Yunnan province. Much of the Chinese work on T. piniperda has until now been inaccessible to the western world, but starting with Ye (1991), an increasing number of papers are now being published in English (see Långström et al., 2002; Lieutier et al., 2003).
Dozens of North American publications have appeared on T. piniperda over the past decade (e.g. Haack and Poland, 2001; Kennedy and McCullough, 2002). Current knowledge on the biology of T. piniperda is summarized for, and compared between, Europe, southern China and North America as follows.
In northern Europe and North America, the adults of T. piniperda hibernate in short galleries in the bark at the base of standing pine trees, but elsewhere they seem to hibernate mainly in the shoots. Spring flight is the main period of dispersal and takes place in early spring when temperatures reach 12°C in the shade (flight threshold was 11°C in Saarenmaa's (1989) swarming model). This dispersal is dependent on latitude and annual variation and may occur in November-December in southern China (Li et al., 1993), January-February in the Mediterranean (Halperin, 1978), February-March in central Europe (Sauvard, 1988) and April-May in Fennoscandia (Långström, 1983). On the basis of flight and climatic data, the average peak flight of T. piniperda in North America would be February and April, at the southern and northern ends of its area of occurrence (Poland et al., 2002), corresponding to the situation in central and northern Europe.
The flying beetles respond to host odours, mainly alpha-pinene, which guide the beetles to the host material (Kangas et al., 1971; Vité et al., 1986; Byers et al., 1985; Lanne et al., 1987; Schroeder, 1988). According to Byers et al. (1989), the beetles may even recognize suitable host trees in flight. Until recently, there has been a consensus that T. piniperda lacks aggregation pheromones (Lanne et al., 1987; Löyttyniemi et al., 1988; but see also, Schönherr, 1972), but recently Poland et al. (2003) concluded that trans-verbenol may act as an aggregation pheromone in T. piniperda.
During the flight period, the females find and colonize suitable host material, i.e. fresh timber or weakened standing trees. In Europe and North America, T. piniperda mainly attacks the lower stem, which is covered with thick corky bark, whereas in China it seems to predominate on the upper part of the pine stem, which is covered with smooth bark (Långström, 1984; Ye and Ding, 1999). T. piniperda is monogamous and the female always excavates the egg gallery, which runs along the wood grain. On standing trees, the galleries are oriented upwards, but on fallen stems they may be oriented towards the base or the top. The gallery starts with a short sterile section, followed by a section with egg niches regularly spaced on both sides, and ends with another sterile section. The length of the gallery varies with attack density from 4-5 cm at high density to more than 10 cm at low density. Egg numbers can be derived from gallery lengths and densities (Saarenmaa, 1983).
T. piniperda has two main fungal associates among the blue-stain fungi: Leptographium wingfieldii and Ophiostoma minus. Only a part of the population seems to carry these fungi (Lieutier et al., 1989; Gibbs and Inman, 1991; Solheim and Långström, 1991) and their role in the biology of the beetle is not fully clarified. However, when inoculated into trees, these fungi alone can kill pine trees with reduced foliage (Solhein et al., 1993) and can grow well in the low oxygen levels of living xylem tissue (Solheim et al., 2000). Thus, they seem to play a similar role to the fungal associates of other aggressive bark beetles (such as Ips typographus) in overwhelming the resistance of live trees, but this is still under debate (cf. Lieutier, 2002).
The larvae feed on the phloem and construct winding galleries perpendicular to the egg galleries, which end in a pupal chamber in the bark or partly in the outer xylem. The pupal period is short, and the callow adults emerge via individual exit holes in the bark. In northern Europe, emergence takes place mainly during July, but varies with weather conditions. Development is faster than in Tomicus minor, and in Sweden the time from mean flight to mean emergence was recorded as 92±12 days with a thermal sum of day-degrees exceeding 0°C of 1016±79 (Långström, 1983). The immature stages do not survive the winter in Scandinavia (Bakke, 1968). In more southerly areas, emergence takes place earlier, but in these areas the occurrence of sister broods blurs the picture. This also appears to be the case in Yunnan, China (Li et al., 1993), but the time from mean flight to mean emergence ranged from 86 to 94 days in two separate laboratory studies (Chen, 2003; Zhao, 2003). In North America, the development and emergence times agreed with those for central and northern Europe. In Ontario, Canada, the thermal sum for the development period was 1250±73 day-degrees (Ryall and Smith, 2000).
There has been considerable discussion over the years about the number of generations and sister broods in pine shoot beetles per year. The statement by Ritchie (1917) that there is only one generation per year but that sister broods exist (i.e. new brood(s) by the same parent beetles in the same year) still holds for regions as different as Sweden (Långström, 1983), France (Sauvard, 1988, 1989), southern China (Långström et al., 2002) and Ontario, Canada (Ryall and Smith, 2000). In contrast, T. destruens has two overlapping generations per year in Italy (Nanni and Tiberi, 1997).
The occurrence of sister broods in T. piniperda increases from north to south. In Sweden, sister broods are rare although the thermal sum in most years would allow a sister brood in the southern part of the country (Långström, 1983). Ryall and Smith (2000) found that two broods occurred in Canada, and that the thermal sum required was lower (856 day-degrees) for the second brood. In France, Sauvard (1993) found four waves of oviposition, i.e. the initial wave and three sister broods, under semi-natural conditions. He also concluded that in France, ca 50% of the total beetle production comes from sister broods. Similarly, Srot (1968) and Lutyk (1988) have observed one or more sister broods in central Europe resulting in an extended period of beetle emergence lasting into September. The situation in China is not clear, but the occurrence of shoot-feeding beetles throughout most of the year indicates the existence of sister broods (Li et al., 1993; Långström et al., 2002).
During oviposition, the male stays in the gallery and removes the frass, but towards the end of the oviposition period, it leaves the gallery and flies to the pine crowns to feed in the shoots in order to regain sexual maturity. A few weeks later, when the females have finished oviposition in early summer, they may be found feeding in the shoots. This pattern has been seen in Sweden (Långström, 1983) and Canada (Ryall and Smith, 2000) and probably also holds true for southern China (Li et al., 1993; Långström et al., 2002).
At least in Fennoscandia, some of the adult beetles may hibernate for a second time, after a period of regeneration feeding in the shoots, and produce another brood the following year (Långström, 1983; Schroeder and Risberg, 1989). Whether this phenomenon also occurs in a warmer climate is not known, but it could well be the case considering the univoltine life cycle and the occurrence of postreproductive adults in the shoots even in southern China (Långström et al., 2002).
The main shoot-feeding period takes place when the callow adults emerge and fly to nearby pine crowns, where they tunnel mainly the current shoots at the outer parts of the branches. In Sweden, this takes place from July to October. The first severe frosts cause the beetles to leave the shoots and move to the base of standing pine trees, where they hibernate in short galleries made in the thick bark (Långström, 1983). The same pattern has been observed in North America (Kauffman et al., 1998; Ryall and Smith, 2000; Poland et al., 2002). In Yunnan, China, this period is more flexible as the life cycle is less synchronized, but the main shoot-feeding period seems to be May to November (Långström et al., 2002).
The parent beetles also move to the shoots for a regeneration-feeding period that starts earlier, and lasts longer, than that of the callow beetles. In Sweden, this regeneration feeding takes place in the previous year's shoots as the current shoots are seldom attacked while expanding (Långström, 1983). A similar pattern regarding the maturation feeding of re-emerging parent beetles has been observed in Canada (Ryall and Smith, 2000). Långström (1983) found that some beetles entered the shoots soon after the flight period and stayed there for the whole summer. As these beetles were sexually nature, he concluded that they had turned to the shoots after exhausting their fat reserves during the search for host material. There are no clear data demonstrating the presence of regeneration feeding after flight or oviposition among parent beetles in the southern parts of the distribution area of T. piniperda. It probably exists, but to what extent is not known.
In T. piniperda, shoot feeding preferentially takes place in the upper whorls of the pine crown (Führer and Kerck, 1978b; Långström, 1983; Kauffman et al., 1998). Långström (1980) concluded that the beetles colonize the crown from above, and that the outermost shoots are taken first. In Sweden, the preferred shoot diameter is ca 3-4 mm and, on average, each beetle tunnelled one shoot, although multiple attacks (same beetle in several shoots or more than one beetle in the same shoot) were not uncommon (Långström, 1980, 1983). In general, the previous year's shoots are tunnelled in early season and the current shoots in late season. This pattern in Sweden was also largely confirmed for North America (Kauffman et al., 1998; Haack et al., 2000, 2001) although, in one year, Ryall and Smith (2000) found that beetles consumed as many as five or six shoots per beetle. The shoots of Yunnan pine (Pinus yunnanensis) are generally longer and thicker, hence the mean diameter of shoot tunnelled was 7-8 mm (Ye, 1996).
There is another important behavioural difference in the Yunnan populations of T. piniperda (which may in fact be another species) in that the beetles may move directly from the shoots to the trunk (Lieutier et al., 2003). Thus, intensive shoot feeding may predispose trees to successive stem attacks, and this situation is aggravated by the fact that the beetles sometimes aggregate for shoot feeding on certain tree individuals (Ye and Lieutier, 1997). In this way, the beetles may create their own breeding materials and this may explain the hitherto unique beetle outbreak in Yunnan. Nothing similar has ever been observed, although intensive shoot feeding in a few cases has triggered stem attacks around sawmills or timber yards in England, UK (Hanson, 1937) and the USA (Czokajlo et al., 1997).
Natural enemies
Top of page| Natural enemy | Type | Life stages | Specificity | References | Biological control in | Biological control on |
|---|---|---|---|---|---|---|
| Allantonema morosa | Parasite | |||||
| Beauveria bassiana | Pathogen | Italy | Pinus | |||
| Coeloides abdominalis | Parasite | |||||
| Coeloides melanostigma | Parasite | |||||
| Corticeus longulus | Predator | Eggs; Arthropods|Larvae | ||||
| Dendrosoter middendorffii | Parasite | Italy | ||||
| Epuraea marseuli | Predator | |||||
| Epuraea unicolour | Predator | |||||
| Glischrochilus quadripunctatus | Predator | |||||
| Heterorhabditis bacteriophora | Parasite | |||||
| Parasitaphelenchus ateri | Parasite | |||||
| Parasitaphelenchus papillatus | Parasite | |||||
| Parasitorhabditis piniperdae | Parasite | |||||
| Platysoma lineare | Predator | |||||
| Plegaderus vulneratus | Predator | |||||
| Rhizophagus depressus | Predator | Eggs; Arthropods|Larvae | ||||
| Rhizophagus parvulus | Predator | |||||
| Rhopalicus brevicornis | Parasite | |||||
| Rhopalicus tutela | Parasite | |||||
| Thanasimus dubius | Predator | Adults; Arthropods|Larvae; Arthropods|Pupae | ||||
| Thanasimus formicarius | Predator | Adults; Arthropods|Larvae; Arthropods|Pupae | Italy | Pinus |
Notes on Natural Enemies
Top of page
Escherich (1923) reports a large number of natural enemies in T. piniperda, and Hanson (1937) gives a thorough description of the predators and parasites of the pine shoot beetles in England, UK. Ounap (2001) lists 52 species of natural enemies from Estonia: most are predators found in the beetle galleries (32 species) or on the bark (11 species) and the remaining nine species are parasitoids. Most of these natural enemies attack a wide range of bark beetles. Among these, larvae of different Medetera flies (Diptera, Dolichopodidae) stand out as one important group, as do certain beetles of the family Rhizophagidae. None of these species is specific to T. piniperda, but three Medetera species (M. dichrocera, M. setiventris and especially M. signaticornis) are frequently also found in Tomicus galleries (Ounap, 2001). Among the predatory beetles, the clerid beetle Thanasimus formicarius and the rhizophagid Rhizophagus depressus are the most common (Ounap, 2001). Hypophloeus longulus is considered an important predator on pine shoot beetles and other bark beetles in Bryansk, Russia (Pishchik, 1980).
Parasitic wasps of the superfamily Chalcidoidea and the family Braconidae are well known parasitoids of bark beetles and several species also attack T. piniperda, but not exclusively (Ounap, 2001). One species, Dinotiscus colon, was only found with T. piniperda or T. minor, whereas two more species were exclusively found with T. minor (Ounap, 2001). Hedqvist (1963) lists 10 species of Chalcidoidea for T. piniperda, but all are shared with other bark beetles. He concluded his grand work on Swedish Chalcidoidea with a complete catalogue (Hedqvist, 2003). Recently, Hedqvist (1998) also concluded his work on Braconidae as bark beetle parasitoids, in which he reared three species from T. piniperda (and T. minor) and lists six more based on literature records, but gives no information about their importance as natural enemies.
Jakaitis (1979) found seven important parasitoids (three braconids and four chalcidids) on pine and spruce bark beetles in Lithuania. One of these parasitoids, Coeloides melanostigma, used T. piniperda and Ips typographus as hosts during the spring and summer generations, respectively.
In Canada, Bright (1996) reported that a number of native predators and parasitoids had been recorded from galleries of T. piniperda, indicating that native natural enemies had quickly found the newly introduced beetle species. The native clerid beetle Thanasimus dubius was also observed to prey upon T. piniperda in Michigan, USA (Kennedy and McCullough, 2002).
The role of natural enemies and diseases in population regulation of T. piniperda is not well understood. According to Hanson (1937), pathogens are of minor importance compared to predators and pathogens. Nematodes are well known parasites in bark beetles (Kurashvili et al., 1981; Tomalak et al., 1984), but for some reason these seem to have been better studied in T. minor than in T. piniperda, and hence are discussed more under the former species. Recently, Kohlmayr et al. (2003) described a new microsporidian that was infecting T. piniperda. There is very little published information on diseases in T. piniperda, although Beauveria bassiana has been tested for biological control.
However, the thorough work by Herard and Mercadier (1996) in central France, demonstrates that natural enemies are important mortality factors in T. piniperda. They found that predators (T. formicarius, R. depressus and Medetera sp.) were the dominant natural enemies early in the season, whereas parasitoids (mainly Rhopalicus brevicornis, R. tutela, Coeloides abdominalis, C. melanostigma and Dendrosoter middendorffi) occurred in late season. On the basis of prey consumption rates, they concluded that T. formicarius and R. depressus are important predators, the former on adults and larvae and the latter on eggs and young larvae, but no quantitative estimates are given. The parasitoids mainly attacked late-instar larvae and pupae, and the last mentioned species D. middendorffi was the most common (75 adults per m³ bark surface).
Much attention has been paid to the clerid beetle Thanasimus formicarius, which is known to be a voracious predator of bark beetles in the larval and imaginal stages (Escherich, 1923; Hanson, 1937; Mazur, 1973; Yuksel et al., 2001). In Poland, Gidaszewski (1974) calculated that this predator caused ca 50-80% mortality in the p brood of T. piniperda. Cage studies in Sweden have shown that this clerid can reduce the production of offspring in T. piniperda by 80-90% (Schroeder, 1996). In comparison, the other predator studied, R. depressus, caused only 40% reduction, and rearing the host with both predators did not exceed the effect beyond that of T. formicarius alone (Schroeder, 1996).
In a similar experiment, Schroeder and Weslien (1994) demonstrated that the longhorn beetle Acanthocinus aedilis, which often attacks the same part of the pine stem as T. piniperda, also reduced Tomicus offspring by ca 80% when reared together, compared with 90% for T. formicarius. The combined effect of both predators was the same as for T. formicarius alone, as each had a negative effect on the other (Schroeder and Weslien, 1994).
Although woodpeckers often visit and peck on trees attacked by bark beetles, experiments have demonstrated that they often arrive late in the season when the pine shoot beetles have left the trees, and mainly prey upon the larvae of pine weevils and longhorn beetles (Nuorteva and Saari, 1980).
Altogether, the capacity of natural enemies to regulate pine shoot beetle (and other bark beetle) populations remains unclear. They certainly contribute to maintaining endemic populations, but in an outbreak situation (e.g. a large storm felling with abundant brood material) they cannot keep up with the pest eruption, but may play a role in the termination of an outbreak. In the population dynamics of T. piniperda, the availability of host material is the key factor determining the potential population level which is then modified by intraspecific competition and natural enemies.
Parasitic wasps of the superfamily Chalcidoidea and the family Braconidae are well known parasitoids of bark beetles and several species also attack T. piniperda, but not exclusively (Ounap, 2001). One species, Dinotiscus colon, was only found with T. piniperda or T. minor, whereas two more species were exclusively found with T. minor (Ounap, 2001). Hedqvist (1963) lists 10 species of Chalcidoidea for T. piniperda, but all are shared with other bark beetles. He concluded his grand work on Swedish Chalcidoidea with a complete catalogue (Hedqvist, 2003). Recently, Hedqvist (1998) also concluded his work on Braconidae as bark beetle parasitoids, in which he reared three species from T. piniperda (and T. minor) and lists six more based on literature records, but gives no information about their importance as natural enemies.
Jakaitis (1979) found seven important parasitoids (three braconids and four chalcidids) on pine and spruce bark beetles in Lithuania. One of these parasitoids, Coeloides melanostigma, used T. piniperda and Ips typographus as hosts during the spring and summer generations, respectively.
In Canada, Bright (1996) reported that a number of native predators and parasitoids had been recorded from galleries of T. piniperda, indicating that native natural enemies had quickly found the newly introduced beetle species. The native clerid beetle Thanasimus dubius was also observed to prey upon T. piniperda in Michigan, USA (Kennedy and McCullough, 2002).
The role of natural enemies and diseases in population regulation of T. piniperda is not well understood. According to Hanson (1937), pathogens are of minor importance compared to predators and pathogens. Nematodes are well known parasites in bark beetles (Kurashvili et al., 1981; Tomalak et al., 1984), but for some reason these seem to have been better studied in T. minor than in T. piniperda, and hence are discussed more under the former species. Recently, Kohlmayr et al. (2003) described a new microsporidian that was infecting T. piniperda. There is very little published information on diseases in T. piniperda, although Beauveria bassiana has been tested for biological control.
However, the thorough work by Herard and Mercadier (1996) in central France, demonstrates that natural enemies are important mortality factors in T. piniperda. They found that predators (T. formicarius, R. depressus and Medetera sp.) were the dominant natural enemies early in the season, whereas parasitoids (mainly Rhopalicus brevicornis, R. tutela, Coeloides abdominalis, C. melanostigma and Dendrosoter middendorffi) occurred in late season. On the basis of prey consumption rates, they concluded that T. formicarius and R. depressus are important predators, the former on adults and larvae and the latter on eggs and young larvae, but no quantitative estimates are given. The parasitoids mainly attacked late-instar larvae and pupae, and the last mentioned species D. middendorffi was the most common (75 adults per m³ bark surface).
Much attention has been paid to the clerid beetle Thanasimus formicarius, which is known to be a voracious predator of bark beetles in the larval and imaginal stages (Escherich, 1923; Hanson, 1937; Mazur, 1973; Yuksel et al., 2001). In Poland, Gidaszewski (1974) calculated that this predator caused ca 50-80% mortality in the p brood of T. piniperda. Cage studies in Sweden have shown that this clerid can reduce the production of offspring in T. piniperda by 80-90% (Schroeder, 1996). In comparison, the other predator studied, R. depressus, caused only 40% reduction, and rearing the host with both predators did not exceed the effect beyond that of T. formicarius alone (Schroeder, 1996).
In a similar experiment, Schroeder and Weslien (1994) demonstrated that the longhorn beetle Acanthocinus aedilis, which often attacks the same part of the pine stem as T. piniperda, also reduced Tomicus offspring by ca 80% when reared together, compared with 90% for T. formicarius. The combined effect of both predators was the same as for T. formicarius alone, as each had a negative effect on the other (Schroeder and Weslien, 1994).
Although woodpeckers often visit and peck on trees attacked by bark beetles, experiments have demonstrated that they often arrive late in the season when the pine shoot beetles have left the trees, and mainly prey upon the larvae of pine weevils and longhorn beetles (Nuorteva and Saari, 1980).
Altogether, the capacity of natural enemies to regulate pine shoot beetle (and other bark beetle) populations remains unclear. They certainly contribute to maintaining endemic populations, but in an outbreak situation (e.g. a large storm felling with abundant brood material) they cannot keep up with the pest eruption, but may play a role in the termination of an outbreak. In the population dynamics of T. piniperda, the availability of host material is the key factor determining the potential population level which is then modified by intraspecific competition and natural enemies.
Means of Movement and Dispersal
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Natural Dispersal (non-biotic)
The adult beetles are good flyers, and can probably cover several kilometres during their spring flight, as indicated by flight mill studies (Forsse, 1989), which also indicate that the callow adults fly less when they leave the brood logs for the pine crowns. Other studies have shown that bark beetles can cover long distances in flight in the search for host material (Nuorteva and Nuorteva, 1968; Nilssen, 1984).
Movement in Trade
T. piniperda has been accidentally introduced to North America where it established in the mid-1990s.
The adult beetles are good flyers, and can probably cover several kilometres during their spring flight, as indicated by flight mill studies (Forsse, 1989), which also indicate that the callow adults fly less when they leave the brood logs for the pine crowns. Other studies have shown that bark beetles can cover long distances in flight in the search for host material (Nuorteva and Nuorteva, 1968; Nilssen, 1984).
Movement in Trade
T. piniperda has been accidentally introduced to North America where it established in the mid-1990s.
Plant Trade
Top of page| Plant parts liable to carry the pest in trade/transport | Pest stages | Borne internally | Borne externally | Visibility of pest or symptoms |
|---|---|---|---|---|
| Stems (above ground)/Shoots/Trunks/Branches | arthropods/adults; arthropods/eggs; arthropods/larvae; arthropods/nymphs; arthropods/pupae | Yes | Pest or symptoms usually visible to the naked eye |
| Plant parts not known to carry the pest in trade/transport |
|---|
| Leaves |
Wood Packaging
Top of page| Wood Packaging liable to carry the pest in trade/transport | Timber type | Used as packing |
|---|---|---|
| Solid wood packing material with bark | Pines | Yes |
| Wood Packaging not known to carry the pest in trade/transport |
|---|
| Loose wood packing material |
| Non-wood |
| Processed or treated wood |
| Solid wood packing material without bark |
Impact
Top of page
The economic impact caused by the pine shoot beetles is threefold: firstly, growth losses may be caused by extensive shoot-feeding in the pine crowns; secondly, stem attacks cause tree mortality; and thirdly, deterioration of timber quality may occur due to beetle-vectored blue-staining of saw logs and pulpwood.
In T. piniperda, the third type of damage is the least problem, mainly because the forest industry has developed routines to avoid timber damage by timber insects including pine shoot beetles. Compared to T. minor, the blue-staining caused by T. piniperda occurs less frequently in timber and is often more superficial, but it still poses a major problem, as indicated by a series of Finnish studies, because T. piniperda is so common (Löyttyniemi and Uusvaara, 1977; Uusvaara and Löyttyniemi, 1978). Recently, sap staining of Korean pine logs due to T. piniperda attack was reported as a timber storage problem in Korea (Kim et al., 2002). No estimates of the economic losses due to blue-staining caused by T. piniperda are available, but the presence of any blue-staining in conifer saw logs reduces the value to a fraction (ca 20%) of the price of prime timber on the timber market, hence, saw mills have developed timber handling practices that minimise insect damage. Although some blue-staining is acceptable in pulpwood, there is a cost connected to the processing of blue-stained timber, as more chemicals are needed for bleaching (Löyttyniemi et al., 1978).
In contrast to the spruce bark beetle (Ips typographus) and a few other aggressive bark beetles, T. piniperda cannot overwhelm and kill healthy pine trees, probably because it lacks aggregation pheromones. Thus, tree mortality due to pine shoot beetle attacks occurs only when trees are weakened by some other cause such as defoliation, fire damage, drought stress, flooding, etc. There are several European examples of defoliator outbreaks rendering pine trees susceptible to pine shoot beetle attacks (Saalas, 1929; Butovitsch, 1946; Lekander, 1953; Crooke, 1959; Habermann and Geibler, 2001; Långström et al., 2001; Cedervind et al., 2003), but tree mortality varies from a few to more than 50% of trees. In the worst case, 2 years of severe to total defoliation led to ca 50% pine mortality over a 5-year period, half of which was attributed to T. piniperda, whereas stands sprayed with Dimilin suffered 1 year of defoliation, no mortality and modest growth losses (Långström et al., 2001). In another case, beetles caused substantial tree mortality after 1 year of defoliation (Crooke, 1959), whereas normally such defoliation would result in only a few and mainly suppressed trees dying from subsequent beetle attack (Lekander, 1953; Cedervind et al., 2003). Each defoliation case is unique and difficult to generalise; however, in most cases studied, trees with less than 10% of the normal foliage left are in great danger of fatal beetle attacks, whereas trees with more than 30% foliage are safer.
Pine trees may also become susceptible to Tomicus attack by fungal diseases. There is one report from Denmark (Jörgensen and Bejer-Petersen, 1951) and from Poland (Sierpinski, 1969), and several from Russia (Bogdanova, 1988, 1998; Kolomiets and Bodganova, 1992) showing that the root rot fungus (Heterobasidion annosum) may predispose pine trees to fatal attacks by T. piniperda. Similarly, pine shoot beetle attacks have followed outbreaks of the fungal shoot disease (Gremmeniella abietina) in Fennoscandian pine forests (Kaitera and Jalkanen, 1994; Cedervind, 2003). Industrial pollution may also render pine trees susceptible to beetle attacks (Sierpinski, 1971; Krol, 1980; Duda, 1981; Oppermann, 1985; Heliövaara and Väisänen, 1991; Kolomiets and Bogdanova, 1998). Forest fires, which are an integral part of the boreal pine ecosystem, have often been found to render trees susceptible to pine shoot beetle attacks in both northern (Galaseva, 1976; Agafonov and Kuklin, 1979; Bogdanova, 1986; Ehnström et al., 1995; Luterek, 1996; Långström et al., 1999) and southern (Markalas, 1997; Fernandez and Costas, 1999) parts of the pest's distribution range.
Only in the Mediterranean region, does significant tree mortality occur on seemingly healthy or only slightly weakened trees of different pine species due to stem attacks by T. piniperda and/or T. destruens (Triggiani, 1983; Ben Jamaa et al., 2000). Drought stress probably caused a major outbreak of T. piniperda and other bark beetles in central France in the 1980s (Sauvard et al., 1988). Only at exceptional attack densities can beetles kill seemingly healthy pines in Scandinavia (Långström and Hellqvist, 1993).
The situation in China differs drastically from that in Europe, in that large-scale tree mortality attributed to T. piniperda has occurred in plantations of Yunnan pine (Pinus yunnanensis) during the past decade (Ye, 1991; Lieutier et al., 2003). Although these trees may suffer some drought stress from time to time, another more important explanation for these outbreaks is that intensive shoot damage may render the trees susceptible to further stem attacks, leading to a vicious self-perpetuating cycle (Lieutier et al., 2003). There are also signs of beetle aggregation during shoot feeding to certain tree individuals (Ye and Lieutier, 1997). There is now some evidence that this beetle, hitherto referred to as T. piniperda, may in fact be another Tomicus species (Lieutier et al., 2003).
In Europe, the growth losses following shoot feeding by pine shoot beetles constitute the main problem, and most of that is due to T. piniperda (Escherich, 1923; Hanson, 1937; Speight and Wainhouse, 1989). These growth losses have mainly been studied in Sweden (Mattson-Mårn, 1921; Andersson, 1973; Nilsson, 1974, 1976; Långström and Hellqvist, 1990, 1991) and Poland (Michalski and Witkowski, 1960; Borkowski, 2001). All of these studies demonstrate a reduction in growth with increasing damage levels, but growth reduction is easier to quantify than levels of damage. Nilsson (1974) claimed that high growth losses occurred at an estimated damage level of 100-150 lost shoots per tree (calculated from felled trees at the end of the study period); however, experiments with caged beetles or artificial shoot pruning did not verify this damage/loss relationship (Ericsson et al., 1985; Långström et al., 1990), implying that the damage levels were underestimated by Nilsson (1974). Later, Långström and Hellqvist (1991) established that 3 years of timber storage resulted in ca 1000 lost shoots, corresponding to more than half of the total needle biomass and a 75% loss in volume growth during the 3-year period (and 65% in basal area growth response during 6 years) on nearby trees. Damage levels and growth losses declined quickly with increasing distance to the timber yard, but could still be traced at a distance of 500 m. Borkowski (2001) found a similar pattern, with radial increment reduced to ca 50% within 300 m from the saw mill, and the number of fallen shoots more than five-fold in that area compared to more distant areas. A similar case was reported from New York State, USA (Czokajlo et al., 1997).
During the large bark beetle outbreaks in Sweden following the huge wind-throw in autumn 1969, when ca 20 million m³ of pine and spruce blew down, Nilsson (1976) estimated that pine shoot beetles caused growth losses in Sweden of several million cubic metres per year in the early 1970s. These figures were based on nation-wide surveys of fallen shoots, which were converted to growth losses, but these losses were overestimated as they were based on his damage/loss ratios (Nilsson, 1974) discussed above.
The number of fallen shoots can be used to estimate the size of the local population of pine shoot beetles. It has been said that one shoot roughly corresponds to one beetle, at least under Swedish conditions. The fallen shoots are best counted in early spring and are often expressed per square metre of soil surface, and knowing the stem density, the attack level per tree can be derived. In well-managed Swedish pine forests with only occasional suppressed trees dying in the stands, the baseline level seems to be around 0.2 shoots per m² and year corresponding to ca 2000 beetles per hectare and a few beetles per tree, with a stem density ranging from ca 2000 in pole-sized stands to ca 500 in mature pine stands (Långström and Hellqvist, 1990; Ehnström et al., 1995). In a Polish study, the baseline figure was around 0.5 shoots/m² (Borkowski, 2001). In central France, the corresponding figure ranged from 0.2 to 0.4 shoots/m², but the presence of any kind of brood material was directly reflected in elevated numbers of shoots and beetles (Sauvard et al., 1987).
In early thinnings or precommercial cleanings, the stumps produced a few tens of beetles per stump increasing linearly with stump diameter (range 5-15 cm), while the corresponding cut stem produced up to 200 beetles (no T. minor, only T. piniperda) per tree (Långström, 1979). Maximum shoot numbers were ca 20 shoots/m² corresponding to population levels of ca 200,000 beetles per ha, and ca 200 lost shoots per tree. The expected volume growth loss after this 1-year attack should have been ca 10% during a 5-year period (cf. Elfving and Långström, 1984; Ericsson et al., 1985). In older thinning stands, the logs are removed and hence only the stumps and the slash are available for the beetles to breed in. Consequently, Doom and Luitjes (1971) found in The Netherlands that beetle levels were low in thinnings when the stems were removed, and that leaving the stems caused severe shoot damage, ca 20 foliage losses.
In clear cuts in Sweden, mature pine stumps produced, on average, ca 150 pine shoot beetles (T. piniperda only) per stump (Hellqvist, 1984). The logging waste, i.e. the cut tree tops, produced no beetles of T. piniperda (bark too thin), whereas a highly variable number of T. minor beetles could be produced in the tops. In one case, the number of egg galleries increased from zero to more than a thousand when the diameter (measured at the base of the cut top) increased from 5 to 15 cm, and ca 400,000 beetles were estimated to have emerged per hectare from 250 tops (Lekander, 1974).
Compared to these cases, storm-felled trees as well as snow-breaks may produce substantially more bark beetles, due to the fact that the whole tree may be colonized by pine shoot beetles when both T. piniperda and T. minor are present in the area. Such trees may produce tens of thousands of beetles (mainly T. minor) when they are fully colonized (Långström, 1984), but the occurrence of T. minor is highly variable and unpredictable, even in areas where it should be present (Annila and Petäistö, 1978; Führer and Kerck, 1978a, b; Långström, 1984). In cases of large storm fellings, many trees may escape beetle attack in the first year for two reasons. Firstly, there may not be enough beetles to colonize all the brood material that is suddenly available, and secondly, some of the trees may display residual resistance due to live root contacts fending off the attacking beetles (Annila and Petäistö, 1978; Führer and Kerck, 1978a; Långström, 1984; Saarenmaa, 1987). The abundance in brood material often leads to high brood production in the first year, and in the second year the remaining trees are heavily attacked, and brood production goes down due to intraspecific competition (Annila and Petäistö, 1978; Långström, 1984).
During the 1970s, the main concern regarding pine shoot beetles was related to the widespread storage of unbarked pulp wood in the forests during the swarming and emergence periods of the beetles, which supported high and stable population levels and subsequent common shoot-feeding damage in pine stands, at least in northern Europe (Nilsson, 1976; Speight and Wainhouse, 1989). The colonization of pulpwood stacks by pine shoot beetles (only T. piniperda as T. minor was seldom found below the top layer) varied with latitude, exposure (shading) and type of wood stored (i.e. the proportion of timber with rough bark). More beetles emerged from exposed stacks than from shaded ones in central Sweden (Långström et al., 1984), and in northern Fennoscandia few beetles emerged at all from the inner parts of the stacks (Juutinen, 1978; Saarenmaa, 1985). The mean beetle production per cubic metre of stored timber is therefore very difficult to estimate: Juutinen (1978) gives a figure of 4400 for the upper log layers, but Långström et al. (1984) considered 2000 as a more realistic mean value for this kind of breeding material. A truck load of pulpwood would then produce tens of thousands of beetles that fly to nearby pine stands for shoot feeding and subsequent growth losses. Recognition of this situation and knowing the huge amounts of timber cut annually, for example, in Finland and Sweden, has led to changes in the forest protection legislation in these and other countries, resulting in a drastic reduction in the storage of unbarked timber (see Control).
Poor forest protection practice with common timber storage along forest roads has not only caused shoot damage and growth losses, but has also maintained high beetle populations that can erupt when storm-fellings or snow-breaks suddenly make huge amounts of brood material available locally or on a regional scale, such as occurred in Sweden after the storm in November 1969 when 20 million m³ blew down and started the outbreak of T. piniperda and Ips typographus (Nilsson, 1976). Similar scenarios have occurred in many parts of Europe during the twentieth century (Escherich, 1923; Niemeyer and Thalenhorst, 1974; Luitjes, 1976, 1977; Annila and Petäistö, 1978; Führer and Kerck, 1978a, b; Bychawska, 1983; Winter and Evans, 1990). The economic consequences of these beetle outbreaks have seldom been established.
In T. piniperda, the third type of damage is the least problem, mainly because the forest industry has developed routines to avoid timber damage by timber insects including pine shoot beetles. Compared to T. minor, the blue-staining caused by T. piniperda occurs less frequently in timber and is often more superficial, but it still poses a major problem, as indicated by a series of Finnish studies, because T. piniperda is so common (Löyttyniemi and Uusvaara, 1977; Uusvaara and Löyttyniemi, 1978). Recently, sap staining of Korean pine logs due to T. piniperda attack was reported as a timber storage problem in Korea (Kim et al., 2002). No estimates of the economic losses due to blue-staining caused by T. piniperda are available, but the presence of any blue-staining in conifer saw logs reduces the value to a fraction (ca 20%) of the price of prime timber on the timber market, hence, saw mills have developed timber handling practices that minimise insect damage. Although some blue-staining is acceptable in pulpwood, there is a cost connected to the processing of blue-stained timber, as more chemicals are needed for bleaching (Löyttyniemi et al., 1978).
In contrast to the spruce bark beetle (Ips typographus) and a few other aggressive bark beetles, T. piniperda cannot overwhelm and kill healthy pine trees, probably because it lacks aggregation pheromones. Thus, tree mortality due to pine shoot beetle attacks occurs only when trees are weakened by some other cause such as defoliation, fire damage, drought stress, flooding, etc. There are several European examples of defoliator outbreaks rendering pine trees susceptible to pine shoot beetle attacks (Saalas, 1929; Butovitsch, 1946; Lekander, 1953; Crooke, 1959; Habermann and Geibler, 2001; Långström et al., 2001; Cedervind et al., 2003), but tree mortality varies from a few to more than 50% of trees. In the worst case, 2 years of severe to total defoliation led to ca 50% pine mortality over a 5-year period, half of which was attributed to T. piniperda, whereas stands sprayed with Dimilin suffered 1 year of defoliation, no mortality and modest growth losses (Långström et al., 2001). In another case, beetles caused substantial tree mortality after 1 year of defoliation (Crooke, 1959), whereas normally such defoliation would result in only a few and mainly suppressed trees dying from subsequent beetle attack (Lekander, 1953; Cedervind et al., 2003). Each defoliation case is unique and difficult to generalise; however, in most cases studied, trees with less than 10% of the normal foliage left are in great danger of fatal beetle attacks, whereas trees with more than 30% foliage are safer.
Pine trees may also become susceptible to Tomicus attack by fungal diseases. There is one report from Denmark (Jörgensen and Bejer-Petersen, 1951) and from Poland (Sierpinski, 1969), and several from Russia (Bogdanova, 1988, 1998; Kolomiets and Bodganova, 1992) showing that the root rot fungus (Heterobasidion annosum) may predispose pine trees to fatal attacks by T. piniperda. Similarly, pine shoot beetle attacks have followed outbreaks of the fungal shoot disease (Gremmeniella abietina) in Fennoscandian pine forests (Kaitera and Jalkanen, 1994; Cedervind, 2003). Industrial pollution may also render pine trees susceptible to beetle attacks (Sierpinski, 1971; Krol, 1980; Duda, 1981; Oppermann, 1985; Heliövaara and Väisänen, 1991; Kolomiets and Bogdanova, 1998). Forest fires, which are an integral part of the boreal pine ecosystem, have often been found to render trees susceptible to pine shoot beetle attacks in both northern (Galaseva, 1976; Agafonov and Kuklin, 1979; Bogdanova, 1986; Ehnström et al., 1995; Luterek, 1996; Långström et al., 1999) and southern (Markalas, 1997; Fernandez and Costas, 1999) parts of the pest's distribution range.
Only in the Mediterranean region, does significant tree mortality occur on seemingly healthy or only slightly weakened trees of different pine species due to stem attacks by T. piniperda and/or T. destruens (Triggiani, 1983; Ben Jamaa et al., 2000). Drought stress probably caused a major outbreak of T. piniperda and other bark beetles in central France in the 1980s (Sauvard et al., 1988). Only at exceptional attack densities can beetles kill seemingly healthy pines in Scandinavia (Långström and Hellqvist, 1993).
The situation in China differs drastically from that in Europe, in that large-scale tree mortality attributed to T. piniperda has occurred in plantations of Yunnan pine (Pinus yunnanensis) during the past decade (Ye, 1991; Lieutier et al., 2003). Although these trees may suffer some drought stress from time to time, another more important explanation for these outbreaks is that intensive shoot damage may render the trees susceptible to further stem attacks, leading to a vicious self-perpetuating cycle (Lieutier et al., 2003). There are also signs of beetle aggregation during shoot feeding to certain tree individuals (Ye and Lieutier, 1997). There is now some evidence that this beetle, hitherto referred to as T. piniperda, may in fact be another Tomicus species (Lieutier et al., 2003).
In Europe, the growth losses following shoot feeding by pine shoot beetles constitute the main problem, and most of that is due to T. piniperda (Escherich, 1923; Hanson, 1937; Speight and Wainhouse, 1989). These growth losses have mainly been studied in Sweden (Mattson-Mårn, 1921; Andersson, 1973; Nilsson, 1974, 1976; Långström and Hellqvist, 1990, 1991) and Poland (Michalski and Witkowski, 1960; Borkowski, 2001). All of these studies demonstrate a reduction in growth with increasing damage levels, but growth reduction is easier to quantify than levels of damage. Nilsson (1974) claimed that high growth losses occurred at an estimated damage level of 100-150 lost shoots per tree (calculated from felled trees at the end of the study period); however, experiments with caged beetles or artificial shoot pruning did not verify this damage/loss relationship (Ericsson et al., 1985; Långström et al., 1990), implying that the damage levels were underestimated by Nilsson (1974). Later, Långström and Hellqvist (1991) established that 3 years of timber storage resulted in ca 1000 lost shoots, corresponding to more than half of the total needle biomass and a 75% loss in volume growth during the 3-year period (and 65% in basal area growth response during 6 years) on nearby trees. Damage levels and growth losses declined quickly with increasing distance to the timber yard, but could still be traced at a distance of 500 m. Borkowski (2001) found a similar pattern, with radial increment reduced to ca 50% within 300 m from the saw mill, and the number of fallen shoots more than five-fold in that area compared to more distant areas. A similar case was reported from New York State, USA (Czokajlo et al., 1997).
During the large bark beetle outbreaks in Sweden following the huge wind-throw in autumn 1969, when ca 20 million m³ of pine and spruce blew down, Nilsson (1976) estimated that pine shoot beetles caused growth losses in Sweden of several million cubic metres per year in the early 1970s. These figures were based on nation-wide surveys of fallen shoots, which were converted to growth losses, but these losses were overestimated as they were based on his damage/loss ratios (Nilsson, 1974) discussed above.
The number of fallen shoots can be used to estimate the size of the local population of pine shoot beetles. It has been said that one shoot roughly corresponds to one beetle, at least under Swedish conditions. The fallen shoots are best counted in early spring and are often expressed per square metre of soil surface, and knowing the stem density, the attack level per tree can be derived. In well-managed Swedish pine forests with only occasional suppressed trees dying in the stands, the baseline level seems to be around 0.2 shoots per m² and year corresponding to ca 2000 beetles per hectare and a few beetles per tree, with a stem density ranging from ca 2000 in pole-sized stands to ca 500 in mature pine stands (Långström and Hellqvist, 1990; Ehnström et al., 1995). In a Polish study, the baseline figure was around 0.5 shoots/m² (Borkowski, 2001). In central France, the corresponding figure ranged from 0.2 to 0.4 shoots/m², but the presence of any kind of brood material was directly reflected in elevated numbers of shoots and beetles (Sauvard et al., 1987).
In early thinnings or precommercial cleanings, the stumps produced a few tens of beetles per stump increasing linearly with stump diameter (range 5-15 cm), while the corresponding cut stem produced up to 200 beetles (no T. minor, only T. piniperda) per tree (Långström, 1979). Maximum shoot numbers were ca 20 shoots/m² corresponding to population levels of ca 200,000 beetles per ha, and ca 200 lost shoots per tree. The expected volume growth loss after this 1-year attack should have been ca 10% during a 5-year period (cf. Elfving and Långström, 1984; Ericsson et al., 1985). In older thinning stands, the logs are removed and hence only the stumps and the slash are available for the beetles to breed in. Consequently, Doom and Luitjes (1971) found in The Netherlands that beetle levels were low in thinnings when the stems were removed, and that leaving the stems caused severe shoot damage, ca 20 foliage losses.
In clear cuts in Sweden, mature pine stumps produced, on average, ca 150 pine shoot beetles (T. piniperda only) per stump (Hellqvist, 1984). The logging waste, i.e. the cut tree tops, produced no beetles of T. piniperda (bark too thin), whereas a highly variable number of T. minor beetles could be produced in the tops. In one case, the number of egg galleries increased from zero to more than a thousand when the diameter (measured at the base of the cut top) increased from 5 to 15 cm, and ca 400,000 beetles were estimated to have emerged per hectare from 250 tops (Lekander, 1974).
Compared to these cases, storm-felled trees as well as snow-breaks may produce substantially more bark beetles, due to the fact that the whole tree may be colonized by pine shoot beetles when both T. piniperda and T. minor are present in the area. Such trees may produce tens of thousands of beetles (mainly T. minor) when they are fully colonized (Långström, 1984), but the occurrence of T. minor is highly variable and unpredictable, even in areas where it should be present (Annila and Petäistö, 1978; Führer and Kerck, 1978a, b; Långström, 1984). In cases of large storm fellings, many trees may escape beetle attack in the first year for two reasons. Firstly, there may not be enough beetles to colonize all the brood material that is suddenly available, and secondly, some of the trees may display residual resistance due to live root contacts fending off the attacking beetles (Annila and Petäistö, 1978; Führer and Kerck, 1978a; Långström, 1984; Saarenmaa, 1987). The abundance in brood material often leads to high brood production in the first year, and in the second year the remaining trees are heavily attacked, and brood production goes down due to intraspecific competition (Annila and Petäistö, 1978; Långström, 1984).
During the 1970s, the main concern regarding pine shoot beetles was related to the widespread storage of unbarked pulp wood in the forests during the swarming and emergence periods of the beetles, which supported high and stable population levels and subsequent common shoot-feeding damage in pine stands, at least in northern Europe (Nilsson, 1976; Speight and Wainhouse, 1989). The colonization of pulpwood stacks by pine shoot beetles (only T. piniperda as T. minor was seldom found below the top layer) varied with latitude, exposure (shading) and type of wood stored (i.e. the proportion of timber with rough bark). More beetles emerged from exposed stacks than from shaded ones in central Sweden (Långström et al., 1984), and in northern Fennoscandia few beetles emerged at all from the inner parts of the stacks (Juutinen, 1978; Saarenmaa, 1985). The mean beetle production per cubic metre of stored timber is therefore very difficult to estimate: Juutinen (1978) gives a figure of 4400 for the upper log layers, but Långström et al. (1984) considered 2000 as a more realistic mean value for this kind of breeding material. A truck load of pulpwood would then produce tens of thousands of beetles that fly to nearby pine stands for shoot feeding and subsequent growth losses. Recognition of this situation and knowing the huge amounts of timber cut annually, for example, in Finland and Sweden, has led to changes in the forest protection legislation in these and other countries, resulting in a drastic reduction in the storage of unbarked timber (see Control).
Poor forest protection practice with common timber storage along forest roads has not only caused shoot damage and growth losses, but has also maintained high beetle populations that can erupt when storm-fellings or snow-breaks suddenly make huge amounts of brood material available locally or on a regional scale, such as occurred in Sweden after the storm in November 1969 when 20 million m³ blew down and started the outbreak of T. piniperda and Ips typographus (Nilsson, 1976). Similar scenarios have occurred in many parts of Europe during the twentieth century (Escherich, 1923; Niemeyer and Thalenhorst, 1974; Luitjes, 1976, 1977; Annila and Petäistö, 1978; Führer and Kerck, 1978a, b; Bychawska, 1983; Winter and Evans, 1990). The economic consequences of these beetle outbreaks have seldom been established.
Environmental Impact
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Being an early flyer, T. piniperda may outcompete native bark beetles occupying the same part of the tree, if it becomes established in new areas.
Detection and Inspection
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The presence of pine shoot beetles in the forest is disclosed by fallen and tunnelled shoots on the ground as well as typically stunted pine crowns in cases of high population levels. It is not possible to separate the shoot damage caused by T. piniperda from that caused by T. minor (or T. destruens), unless the beetles are still inside the shoots.
After the spring flight, the adults of T. piniperda disclose their presence in fresh pine timber or weakened trees by the typical boring dust containing brown bark and white wood grain (unique for this species), which is visible in bark crevices adjoining the entrance holes. In late summer, clusters of exit holes (ca 1.5 mm in diameter) reveal successful brood emergence. Peeling off the bark will show the typical longitudinal egg galleries with egg niches in early season, and larval galleries in late season. Egg galleries vary in length with attack density from a few centimetres to more than 10 cm. The same symptoms can be seen on successfully attacked standing trees, whereas failed attacks show resin flow (or crystallised resin) in bark crevices on the bark. Short hibernation tunnels can be found at the tree base. In Europe, T. piniperda normally attacks the lower part of the tree, which is covered with rough bark, whereas in Yunnan, China, it seems to prefer the upper stem (Ye and Ding, 1999).
After the spring flight, the adults of T. piniperda disclose their presence in fresh pine timber or weakened trees by the typical boring dust containing brown bark and white wood grain (unique for this species), which is visible in bark crevices adjoining the entrance holes. In late summer, clusters of exit holes (ca 1.5 mm in diameter) reveal successful brood emergence. Peeling off the bark will show the typical longitudinal egg galleries with egg niches in early season, and larval galleries in late season. Egg galleries vary in length with attack density from a few centimetres to more than 10 cm. The same symptoms can be seen on successfully attacked standing trees, whereas failed attacks show resin flow (or crystallised resin) in bark crevices on the bark. Short hibernation tunnels can be found at the tree base. In Europe, T. piniperda normally attacks the lower part of the tree, which is covered with rough bark, whereas in Yunnan, China, it seems to prefer the upper stem (Ye and Ding, 1999).
Similarities to Other Species/Conditions
Top of pageIn Europe, the longitudinal egg galleries of T. piniperda can be confused with those of Hylurgops palliatus and Hylurgus ligniperda, but in T. piniperda the egg niches occur in a more regular pattern and the lower part of the gallery often has resin-soaked edges. It is probably not possible to distinguish the egg galleries of T. piniperda from those of T. destruens.
Tomicus adults differ from other related Hylesini-like Hylastes sp. and Hylurgops sp. by their shiny body; for more specific characters, it is advisable to consult identification keys (Pfeffer, 1994). The adults of T. minor can be distinguished from those of T. piniperda as described under Morphology. T. piniperda can be separated from T. destruens on the basis of several morphological characters (Faccoli, 2006). It takes an expert to identify bark beetle larvae to species, if they are not found in their galleries, but it can be done (Lekander, 1968).
Prevention and Control
Top of pageDue to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
As both T. piniperda and T. minor are dependent on a continuous supply of suitable host material for their survival, silvicultural and logging practices may greatly affect the population density of these beetles both locally and regionally. The concept of forest hygiene, i.e. keeping the amounts of brood material available for bark beetles during their flight period as low as possible, has long been a key strategy in forest protection (Escherich, 1923; Speight and Wainhouse, 1989; Dajoz, 2000). This means that silvicultural operations should be carried out with a minimum of suitable host material left in the forests, that snow-breaks and wind-falls should be cleared up before beetle attack or at least before beetle emergence, and that the timber should be removed from the woods in due time. All this is easier said than done, and when beetle outbreaks occur, trap trees are the common method used to reduce the populations (e.g. Escherich, 1923; Hanson 1937, 1940).
A major change took place in forestry operations after World War II when the timber, which had until then mainly been debarked in the forests prior to transportation (often by floating), was instead stored unbarked along road sides until it was taken to the industry by trucks. In contrast to earlier practice, forest operations were also conducted all-year-round. This created a entirely new situation with huge amounts of unbarked timber stored in the forests during beetle flight, especially in Fennoscandia, where annual cuttings were large and roads often unaccessible during the thawing period in spring. Little has been written about this phenomenon, leading to constantly elevated bark beetle populations (Eidmann, 1985, 1992; Jääskelä et al., 1997; Day and Leather, 1997).
In Sweden, the huge storm-felling in 1969 when 20 million m³ blew down, resulted in bark beetle outbreaks of unprecedented magnitude (Nilsson, 1976) and a similar situation developed in Finland a few years later (Annila and Petäistö, 1978). These events eventually led to changes in the forestry legislation when forest protection became regulated by law (Eidmann 1985, 1992; Jääskelä et al., 1997). In principle, unbarked timber must not be stored during the flight and emergence of pine and spruce bark beetles, unless certain precautions are taken. In Sweden, up to 5 m³ of storm-felled trees per hectare can and should, according to the current debate about dead wood and biodiversity (Ehnström et al., 1995), be left without countermeasures being taken. Similar legislation exists in other European countries.
Thus, the main option to avoid bark beetle damage was, and still is, rapid transportation (i.e. before beetle flight in spring) of saw logs and pulpwood from the forest to the industry, where it is barked or submerged in water immediately, until processed. In Sweden, where timber storage and fallen Tomicus-attacked shoots were monitored nation-wide through the 1970s and 1980s, a substantial reduction in Tomicus populations was recorded with decreasing timber storage figures. Growth losses nowadays mainly occur around saw and paper mills with constant timber storage (e.g. Långström and Hellqvist, 1990; and many unpublished reports) for at least a decade.
If timely transportation is not feasible, the timber can be protected in different ways. The earlier barking at the felling site is now abandoned as being too expensive. Instead, the timber can be protected by spraying with insecticides, but this has to take place before beetle flight. In the 1980s, synthetic pyrethroids such as permethrin became the main option (Srot, 1968; Doom and Luitjes, 1970; Novak, 1972; Dowding, 1974; Dominik and Kinelski, 1979; Szmidt, 1983; Glowacha and Wajland, 1992). Due to increased environmental concerns, the use of insecticides for timber protection has decreased greatly, at least in Fennoscandia. Also, spraying against the early flying Tomicus species may be tricky under northern conditions, as snow may sometimes still cover part of the timber resulting in poor spray coverage.
Other ways of protecting log piles against bark beetles have been explored. Covering pulpwood stacks with plastic or other coatings has produced variable, but sometimes satisfactory, results, i.e. comparable to insecticide use, in Sweden and Finland (Dehlen and Nilsson, 1976; Heikkilä, 1978; Jääskelä et al., 1997). Partial debarking or removal of the upper layers in the pines also reduced beetle production substantially (Dehlen et al., 1982; Jääskelä et al., 1997) as did sprinkling with water (Regnander, 1976). A more modern approach is based on deterring the beetles from attacking by spraying log piles with verbenone or other substances with deterrent properties (Schlyter et al., 1988; Baader and Vité, 1990; Kohnle et al., 1992; McCullough et al., 1998). Non-host volatiles also show some promise for timber control (McCullough et al., 1998; Zhang, 2001) but none of these techniques has yet attained any wide use in practical forestry.
Baited traps containing host odours, especially alpha-pinene, attract large numbers of pine shoot beetles, and these are excellent for monitoring purposes but give little hope for beetle control. The recent detection of trans-verbenol, which may act as an aggregation pheromone in T. piniperda (Poland et al., 2003), may provide an even better monitoring tool but hardly a control option.
Another important approach to maintaining low beetle populations is related to the timing of silvicultural operations such as cleaning (i.e. precommercial thinning) and thinning of pine stands (Bykov, 1987). In general, late summer operations are preferred as the waste wood is neither attacked in the year of cutting (beetle flight terminated), nor in the following spring (waste wood unsuitable). In Fennoscandia, June to September are considered to be 'Tomicus-safe' months (Långström, 1979; Annila and Heikkilä, 1991), whereas Postner (1974) recommends August for central Europe. Cleanings should preferentially be made before DBH (diameter at 1.3 m stem height) exceeds 3 cm, i.e. before thick bark starts to form on the lower stem and the trees become suitable for T. piniperda (Butovitsch, 1954; Långström, 1979).
Some attempts at biological control of T. piniperda have been made using the entomopathogenic fungus Beauveria bassiana with variable results (Nuorteva and Salonen, 1968; Bychawska and Swiezynska, 1979). Lutyk and Swiezynska (1984) obtained satisfactory results when logs were covered with plastic after spraying with B. bassiana. The introduction of the clerid beetle T. formicarius to North America has been seriously considered (Haack and Poland, 2001) but this approach may now be redundant as the native and closely related clerid T. dubius seems to have adapted to the new prey (Kennedy and McCullough, 2002).
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