Xyleborus dispar (pear blight beetle)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- History of Introduction and Spread
- Risk of Introduction
- Hosts/Species Affected
- Growth Stages
- List of Symptoms/Signs
- Biology and Ecology
- Natural enemies
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Plant Trade
- Wood Packaging
- Impact Summary
- Impact: Biodiversity
- Detection and Inspection
- Similarities to Other Species/Conditions
- Prevention and Control
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Xyleborus dispar (Fabricius, 1792)
Preferred Common Name
- pear blight beetle
Other Scientific Names
- Anisandrus aequalis Reitter
- Anisandrus dispar (Ferrari, 1867)
- Anisandrus dispar rugulosus Eggers, 1922
- Anisandrus pyri (Peck)
- Anisandrus swainei Drake, 1921
- Apate dispar Fabricius, 1792
- Bostrichus brevis Panzer, 1793
- Bostrichus dispar (Herbst, 1793)
- Bostrichus ratzeburgi Kolenati, 1846
- Bostrichus tachygraphus Sahlberg, 1834
- Bostrichus thoracicus Panzer, 1793
- Scolytus pyri Peck, 1817
- Tomicus dispar (Thomson, 1857)
- Tomicus pyri (Harris, 1852)
- Trypodendron dispar (Stephens, 1830)
- Xyleborus cerasi Eggers, 1937
- Xyleborus pyri (Zimmermann, 1868)
International Common Names
- English: ambrosia beetle; beetle, pear blight; European shothole borer; larger shothole borer; shothole borer
- Spanish: barrenador; taladrador; xileboro dispar
- French: bostryche disparate; bostryche dissemblable; xylébore disparate
Local Common Names
- Denmark: barkbille; vedborer, uens
- Finland: lustokuoriainen
- Germany: Borkenkaefer, ungleicher Holz-; Holzbohrer, ungleicher; ungleicher Borkenkäfer; ungleicher Holzbohrer; ungleicher Holzborkenkäfer
- Italy: anisandro dispari; bostrico dispari; xileboro disuguale; xyleboro (bostrico) disuguale
- Netherlands: houtboorkever; ongelijke houtkever; ongelijke houtschorskever
- Norway: lauvtrebarkbille
- Poland: rozwiertek nieparek
- Sweden: loevvedborre, svart
- Turkey: dalkiran
- XYLBDI (Xyleborus dispar)
Summary of InvasivenessTop of page X. dispar should be considered a high-risk quarantine pest. This is because members of the tribe Xyleborini (Xyleborus plus related genera) are all inbreeding, with the males generally mating with their sisters within the parental gallery system before dispersal. Thus the introduction of only a few mated females may lead to the establishment of an active population if suitable host plants can be found and environmental conditions are satisfactory. A very wide range of host plants have been recorded for many species of Xyleborus and related genera. Any woody material of suitable size, moisture content and density may be all that is required. The direct risk of establishment of populations of X. dispar outside its present range should be considered very serious. It is evident that the species has been introduced to new areas, primarily, but not entirely, in temperate and subtropical regions, and to spread within these areas, over at least the past 200 years. Further introductions and spread are likely. Although X. dispar is usually a secondary species, it may become a primary species attacking healthy trees, especially in areas where it is an exotic species (Kühnholz et al., 2003). Such a change in habits considerably increases its potential for causing economic damage to crop and forest trees.
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Metazoa
- Phylum: Arthropoda
- Subphylum: Uniramia
- Class: Insecta
- Order: Coleoptera
- Family: Scolytidae
- Genus: Xyleborus
- Species: Xyleborus dispar
Notes on Taxonomy and NomenclatureTop of page Xyleborus dispar was first described by Fabricius in 1792 as Apate dispar, and has had a long and varied taxonomic history. The many synonyms that have resulted are listed by Bright (1968), Postner (1974), Schedl (1981), Wood (1982), Wood and Bright (1992), Pfeffer (1995) and Mandelshtam (2000). The earlier opinion that X. dispar in Europe and Xyleborus pyri in North America are two different species is no longer held (Bright, 1968). Wood and Bright (1992) include an exhaustive bibliography of references, and this is supplemented by Bright and Skidmore (1997, 2002).
DescriptionTop of page Eggs
Eggs are oval (0.8-0.9 mm x 0.4 mm), pearly white and shiny.
The mature larva has been described in detail and figured by Lekander (1968, as Anisandrus dispar). A few additional characters are given by Kalina (1970). Only characters which can be used to distinguish the species from other European genera of bark and ambrosia beetle larvae are given here. Head capsule and mouthparts unusually wide, head capsule index, 0.84. Antennae conical, not constricted at base. Labrum broad, with four anteromedian setae. Three pairs of median epipharyngeal setae, the posterior two pairs smaller and spine-like. Tormae long, diverging posteriorly, and bent sharply outwards near the anterior end. Mentum short and broad, narrowed posteriorly. Kalina (1975) notes that the larva is more similar to that of Xyleborus cryptographus, and less close to the larvae of Xyleborus monographus and Xyleborinus saxesenii.
The pupa has been described by Nosek (1958), and distinguished from that of Xyleborinus saxesenii. The pupae of scolytids remain poorly known, and taxonomically important characters uncertain.
There is an evident morphological difference between both sexes. The male is much smaller than the female, 1.8-2.4 mm long (about 1.6 times as long as wide) and has a body strongly convex (thorax relatively small and abdomen short). The female is 3.2-3.7 mm long (twice as long as wide) and the body is more elongate and cylindrical than in the male. The female can be distinguished from related European species by the broad pronotum, which is wider than long, the disc finely shagreened, and finely, sparsely punctured; the elytra 1.3 to 1.4 times longer than wide, both disc and declivity with strongly punctured striae, the declivity steep, with minute granules on the interstriae. The males are uncommon, and rarely found outside the gallery system.
Distribution TableTop of page
The 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.
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|Armenia||Present||Native||Not invasive||Stark, 1952; Pfeffer, 1995|
|Azerbaijan||Present||Native||Not invasive||Stark, 1952; Pfeffer, 1995|
|China||Present||Present based on regional distribution.|
|-Heilongjiang||Present||Native||Not invasive||Yin et al., 1984; Wood and Bright, 1992|
|-Shaanxi||Present||Native||Not invasive||Bright and Skidmore, 2002|
|Georgia (Republic of)||Present||Native||Not invasive||Stark, 1952; Pfeffer, 1995|
|Iran||Restricted distribution||Native||Not invasive||Bright and Skidmore, 2002|
|Japan||Absent, intercepted only||Native||Not invasive||Ohno, 1991|
|Mongolia||Present||Native||Not invasive||Yanovskii and Tegshzhargal, 1984|
|Turkey||Restricted distribution||Native||Not invasive||Balachowsky, 1963; Schedl, 1981|
|Algeria||Restricted distribution||Native||Not invasive||Balachowsky, 1963; Postner, 1974; Schedl, 1981|
|Morocco||Restricted distribution||Native||Not invasive||Balachowsky, 1963; Postner, 1974; Schedl, 1981|
|Tunisia||Restricted distribution||Native||Not invasive||Balachowsky, 1963; Postner, 1974; Schedl, 1981|
|Canada||Present||Present based on regional distribution.|
|-British Columbia||Restricted distribution||Introduced||Invasive||Mathers, 1940; Bright, 1968; Wood, 1982|
|-Nova Scotia||Restricted distribution||Introduced||Invasive||Bright, 1968; Wood, 1982|
|-Ontario||Restricted distribution||Introduced||Invasive||Bright, 1968; Wood, 1982|
|-Quebec||Restricted distribution||Introduced||Invasive||Bright, 1968|
|USA||Present||Present based on regional distribution.|
|-California||Restricted distribution||Introduced||Invasive||Linsley and MacLeod, 1942; Hobson and Bright, 1994|
|-Idaho||Restricted distribution||Introduced||Invasive||Bright, 1968; Wood, 1982; Furniss and Johnson, 1987|
|-Illinois||Restricted distribution||Introduced||Invasive||Wood and Bright, 1992|
|-Maine||Restricted distribution||Introduced||Invasive||Bright, 1968; Wood, 1982|
|-Maryland||Restricted distribution||Introduced||Invasive||Wood, 1982|
|-Massachusetts||Restricted distribution||Introduced||Invasive||Bright, 1968; Wood, 1982|
|-Michigan||Restricted distribution||Introduced||Invasive||Bright, 1968; Wood, 1982|
|-Missouri||Restricted distribution||Introduced||Invasive||Roling and Kearby, 1975; Wood, 1982|
|-New Hampshire||Restricted distribution||Introduced||Invasive||Bright, 1968|
|-New Jersey||Restricted distribution||Introduced||Invasive||Bright, 1968; Wood, 1982|
|-New York||Restricted distribution||Introduced||Invasive||Bright, 1968; Wood, 1982|
|-North Carolina||Restricted distribution||Introduced||Invasive||Wood and Bright, 1992|
|-Ohio||Restricted distribution||Introduced||Invasive||Bright, 1968; Wood, 1982|
|-Oregon||Restricted distribution||Introduced||Invasive||Bright, 1968; French and Roeper, 1972; French and Roeper, 1975; Wood, 1982|
|-Pennsylvania||Restricted distribution||Introduced||Invasive||Bright, 1968; Wood, 1982|
|-Rhode Island||Restricted distribution||Introduced||Invasive||Bright, 1968; Wood, 1982|
|-South Carolina||Restricted distribution||Introduced||Invasive||Kovach and Gorsuch, 1985|
|-Utah||Restricted distribution||Introduced||Invasive||Bright, 1968; Wood, 1982|
|-Virginia||Restricted distribution||Introduced||Invasive||Bright, 1968; Wood, 1982|
|-Washington||Restricted distribution||Introduced||Invasive||Bright, 1968; Wood, 1982|
|-West Virginia||Restricted distribution||Introduced||Invasive||Bright, 1968; Wood, 1982|
|Austria||Widespread||Native||Not invasive||Russ, 1966; Egger, 1973|
|Belarus||Restricted distribution||Native||Not invasive||Stark, 1952; Balachowsky, 1963; Postner, 1974; Schedl, 1981; Anon, 1992; Pfeffer, 1995|
|Belgium||Restricted distribution||Native||Not invasive||Balachowsky, 1963; Postner, 1974; Schedl, 1981; Pfeffer, 1995|
|Bosnia-Hercegovina||Restricted distribution||Native||Not invasive||Balachowsky, 1963; Postner, 1974; Schedl, 1981; Pfeffer, 1995|
|Bulgaria||Restricted distribution||Native||Not invasive||Ioakimov, 1925; Tsankov and Ganchev, 1988|
|Croatia||Restricted distribution||Native||Not invasive||Balachowsky, 1963; Postner, 1974; Schedl, 1981; Pfeffer, 1995|
|Czech Republic||Restricted distribution||Native||Not invasive||Balachowsky, 1963; Postner, 1974; Schedl, 1981; Pfeffer, 1995|
|Czechoslovakia (former)||Restricted distribution||Native||Not invasive||Balachowsky, 1963; Postner, 1974; Schedl, 1981; Pfeffer, 1995|
|Denmark||Restricted distribution||Native||Not invasive||Balachowsky, 1963; Postner, 1974; Schedl, 1981; Pfeffer, 1995|
|Estonia||Restricted distribution||Native||Not invasive||Stark, 1952; Voolma, 1996|
|Finland||Restricted distribution||Native||Not invasive||Annila, 1977; Martikainen et al., 2001|
|France||Widespread||Native||Not invasive||Vasseur and Schvester, 1948; Schvester, 1954; Balachowsky, 1963; Juillard-Condat and Perrau, 1989|
|Germany||Widespread||Native||Not invasive||Schik & Thines, 1988; Roediger, 1956; Klimetzek et al., 1986; Schröder, 1996|
|Greece||Restricted distribution||Native||Not invasive||Markalas and Kalapanida, 1997|
|Hungary||Restricted distribution||Native||Not invasive||Balachowsky, 1963; Postner, 1974; Schedl, 1981; Pfeffer, 1995|
|Italy||Restricted distribution||Native||Not invasive||Viggiani, 1979; Zöggeler, 1987|
|Latvia||Restricted distribution||Native||Not invasive||Stark, 1952|
|Liechtenstein||Restricted distribution||Native||Not invasive||Balachowsky, 1963; Postner, 1974; Schedl, 1981; Pfeffer, 1995|
|Lithuania||Restricted distribution||Native||Not invasive||Stark, 1952|
|Luxembourg||Restricted distribution||Native||Not invasive||Balachowsky, 1963; Postner, 1974; Schedl, 1981; Pfeffer, 1995|
|Macedonia||Restricted distribution||Native||Not invasive||Balachowsky, 1963; Postner, 1974; Schedl, 1981; Pfeffer, 1995|
|Moldova||Restricted distribution||Native||Not invasive||Balachowsky, 1963; Postner, 1974; Schedl, 1981; Pfeffer, 1995|
|Netherlands||Widespread||Native||Not invasive||van Frankenhuyzen, 1992|
|Norway||Restricted distribution||Native||Not invasive||Hesjedal and Edland, 1988|
|Poland||Widespread||Native||Not invasive||Lagowska & Winiarska, 1997; Dominik and Kinelski, 1985|
|Romania||Restricted distribution||Native||Not invasive||Bud, 1972|
|Russian Federation||Present||Present based on regional distribution.|
|-Central Russia||Restricted distribution||Native||Not invasive||Stark, 1952; Balachowsky, 1963; Postner, 1974; Schedl, 1981; Anon, 1992; Pfeffer, 1995|
|-Eastern Siberia||Restricted distribution||Native||Not invasive||Stark, 1952; Balachowsky, 1963; Postner, 1974; Schedl, 1981; Anon, 1992; Pfeffer, 1995|
|-Southern Russia||Restricted distribution||Native||Not invasive||Stark, 1952; Balachowsky, 1963; Postner, 1974; Schedl, 1981; Anon, 1992; Pfeffer, 1995|
|-Western Siberia||Restricted distribution||Native||Not invasive||Stark, 1952; Balachowsky, 1963; Postner, 1974; Schedl, 1981; Anon, 1992; Pfeffer, 1995|
|Slovakia||Restricted distribution||Native||Not invasive||Balachowsky, 1963; Postner, 1974; Schedl, 1981; Pfeffer, 1995|
|Slovenia||Restricted distribution||Native||Not invasive||Balachowsky, 1963; Postner, 1974; Schedl, 1981; Pfeffer, 1995|
|Spain||Restricted distribution||Native||Not invasive||Lombardero et al., 1997|
|Sweden||Restricted distribution||Native||Not invasive||Schroeder and Lindelöw, 1989|
|Switzerland||Widespread||Native||Not invasive||Schneider-Orelli, 1913; Mani and Schwaller, 1983; Keimer, 1990|
|UK||Widespread||Native||Not invasive||Duffy, 1953; Alford, 1984|
|Ukraine||Widespread||Native||Not invasive||Stark, 1952; Chepurnaya and Myalova, 1981; Skiba and Parii, 1989; Tyeryent'ev and Stolyarova, 1989|
|Yugoslavia (Serbia and Montenegro)||Restricted distribution||Native||Not invasive||Balachowsky, 1963; Postner, 1974; Schedl, 1981; Pfeffer, 1995|
History of Introduction and SpreadTop of page In Europe, X. dispar is widespread from Spain to the Urals and from Italy to Finland (Stark, 1952; Balachowsky, 1963; Postner, 1974; Schedl, 1981; Pfeffer, 1995).
In Asia, it is known from the Middle East through Siberia to Sakhalin Island and north-eastern China. In Africa, it is present only in the North in Mediterranean countries (Stark, 1952; Balachowsky, 1963; Postner, 1974; Schedl, 1981; Pfeffer, 1995; Yanovskii, 1999).
In North America, where it was accidentally introduced from Europe before 1817 (Wood, 1977), X. dispar now occurs in eastern North America west to the Great Lakes states and south to South Carolina, western Canada, the Pacific Northwest states and California (Linsley and MacLeod, 1942; Bright 1968; Wood, 1982; Kovach and Gorsuch, 1985; Hobson and Bright, 1994). The distribution in North America suggest two introductions, one in the east and one in the west.
Risk of IntroductionTop of page A number of species of Xyleborus and related genera with similar habits to X. dispar have become important pests of tree crops, ornamental and native trees in tropical, subtropical and warm temperate zone areas where they have been introduced. The risk of introduction for X. dispar must be considered high, most probably in the branches of imported plants, although other pathways are also possible. Once established, such species are difficult to eradicate, and are likely to spread with the movement of infested plants, as well as by normal dispersal of the adults. X. dispar is included on the New Zealand Regulated Pest List, and Xyleborus spp. on the APHIS Regulated Pest List in the USA.
Hosts/Species AffectedTop of page X. dispar is very polyphagous. It attacks many deciduous trees, probably all in its distribution range (Schvester, 1954; Balachowsky, 1963; Bright, 1968; Schedl, 1981; Wood, 1982; Wood and Bright, 1992; Pfeffer, 1995). Recently it was also found on Eucalyptus (Lombardero et al., 1997). A few conifers are also mentioned (Bright, 1968; Postner, 1974; Schedl, 1981).
Favoured species are fruit trees, such as apple, apricot, peach, nectarine, pear, cherry, plum, hazel (Mathers, 1940; Linsley and MacLeod, 1942; Vasseur and Schvester, 1948; Schvester, 1954; Balachowsky, 1963; Postner, 1974; Viggiani, 1979; Chepurnaya and Myalova, 1981; Mani and Schwaller, 1983; Kovach and Gorsuch, 1985; Furniss and Johnson, 1987; Hesjedal and Edland, 1988; Schick and Thines, 1988; Juillard-Condat and Perrau, 1989; Schröder, 1996; Lagowska and Winiarska, 1997; Morone and Scortichini, 1998). Of forest trees, maple, oak (Postner, 1974), birch, poplar, alder (Balachowsky, 1963), chestnut (Schvester, 1954; Bud, 1972) and Chinese chestnut (Tsankov and Ganchev, 1988) are mostly attacked. Damage on urban hawthorn trees has also been reported (Nachtigall, 1993).
Growth StagesTop of page Flowering stage, Vegetative growing stage
SymptomsTop of page Attacked trees have delayed growth. Whole trees or part of trees start to wilt and often perish within a short time (especially young fruit trees).
In April/May small, round entry holes (about 2 mm in diameter) become visible in the bark of trunks and larger branches. Fine, white frass trickles out from such holes. In plants still in good health, plant sap or gum (especially in Prunus) flows out of the holes.
In general, X. dispar attacks only stressed trees which are already damaged by frost, drought, wetness, transplanting, root feeders or diseases. The beetle may also attack trees before conspicuous external evidence appears to indicate the stressed condition of the tree. Attacks by X. dispar may be regarded as symptomatic of an altered physiological condition in the tree. However, Vasseur and Schvester (1948), Schvester (1954), Egger (1973), Postner (1974), Viggiani (1979), Schröder (1996) and Perny (1998) report that apparently healthy trees, especially apple, pear, apricot and hazel, may also be attacked. This occurs mainly when insect populations are high.
List of Symptoms/SignsTop of page
|Stems / dieback|
|Stems / gummosis or resinosis|
|Stems / internal feeding|
|Stems / mycelium present|
|Stems / visible frass|
|Whole plant / frass visible|
|Whole plant / internal feeding|
|Whole plant / plant dead; dieback|
|Whole plant / unusual odour|
Biology and EcologyTop of page Almost all of the work on the biology of X. dispar has been carried out in Europe. However, it seems probable that these studies are applicable to North America. X. dispar has one generation per year (Schneider-Orelli, 1913; Schvester, 1954). The opinion of earlier authors, that X. dispar has two generations, may be due to the long flight period of the females and to some young and old females leaving the galleries in summer.
As soon as the maximum daily temperature in spring reaches 18-20°C the female beetles start flying and searching for host plants. This is mostly in April/May, but sometimes as early as March (Schneider-Orelli, 1913; Schvester, 1954; Roediger, 1956; Egger, 1973; Mani and Schwaller, 1983; Mani et al., 1990, 1992; Schröder, 1996). The emergence of the females usually continues for 4-8 weeks depending on weather conditions.
The main flight activity of the beetles is between 14:00 h and 16:00 h (Mani et al., 1990, 1992). In orchards with high populations, a distinct swarming of females was directly observed. Traps in open fields often caught many beetles, indicating that the beetles may fly over long distances. Catches of beetles in traps indicated that the flight in a shady forest started and finished later than in the adjacent orchard (Mani et al., 1990, 1992). A similar situation may be the cause of the unusually long period of trap catches (4 months) observed by Markalas and Kalapanida (1997) in a forest.
After emergence, females may start boring in the same tree in which they have developed, if this is still in a suitable condition, or disperse to find another suitable host plant. The females first bore a short, radial entrance tunnel (1-3 cm deep) before excavating a transverse tunnel to either side. From each of these, cylindrical breeding galleries are produced, directed perpendicularly both upwards and downwards (Schneider-Orelli, 1913; Egger, 1973; Postner, 1974; Alford, 1984; Mani et al., 1990). In smaller trunks or in branches, the galleries are often simpler.
Shortly after the beginning of boring, when the ambrosia fungus has become established, the female starts egg laying. The female then continues excavating the gallery and laying eggs. Larvae emerge a few days after oviposition. Adults and larvae feed on the fungus growing in the tunnels. In June/July pupation takes place and in July/August beetles of the new generation appear. Full development takes about 2 months. Due to the long flight and oviposition period of the females, different developmental stages may be found in a gallery at the same time. Teneral adults enter diapause and are unable to attack trees and to breed. The diapause is terminated during the winter (Schvester, 1954).
Beetles pass the winter in the breeding galleries, tightly packed one behind the other. The following spring, the young females of the new generation leave the gallery system through the parental entrance hole. Brother-sister mating takes place in the gallery. Males are unable to fly and usually die within the parental nest. However, it was noted long ago by Schneider-Orelli (1913) that males can sometimes be found in spring crawling on the bark of attacked trees, and may mate with overwintered females from other galleries. The ratio of males to females is very variable. Egger (1973) found some galleries in which males outnumbered females, but more usually the sex ratio is biased towards females, from 1:5 to 1:15, and occasionally higher. The average number of beetles in a gallery is about 25, depending on the size and quality of the gallery, with a maximum of about 40 (Schneider-Orelli, 1913; Schvester, 1954; Egger, 1973).
X. dispar belongs to the group of ambrosia beetles (Schneider-Orelli, 1913; Francke-Grosmann, 1963; Batra, 1963, 1967; French and Roeper, 1972, 1975). The larvae are exclusively mycetophagous; they do not feed on wood, but on the symbiotic fungus Ambrosiella hartigii, which grows in the tunnels. It grows as a continuous palisade within the galleries of the active brood. A. hartigii has two growth forms. The ambrosial form (conidia and sprout cells) is produced in association with the insect and the mycelial form is produced in vitro without the insect. French and Roeper (1972) found that larvae feed on the mycelial form in vitro, but ambrosia is required by the larvae to develop and pupate. They also believe that the main mechanism for ambrosia induction and control involves a secretion of the insect. Oocyte development and oviposition occurred only after the post-diapause females had fed on the ambrosial form of the fungus. French and Roeper (1975) also observed a tending and nursing behaviour of the females. The quality of the host tissues affects fungal growth.
The fungus is transferred by the mother beetle to the new gallery in a mycangium (Batra, 1963, 1967). In X. dispar, the mycangia are paired, pocket-shaped organs situated underneath the mesonotum (Francke-Grosmann, 1956; Batra, 1963).
Natural enemiesTop of page
Notes on Natural EnemiesTop of page The immature stages of xyleborines have few natural enemies. The female parent normally remains in the gallery entrance whilst the immature stages are developing, preventing the entry of potential predators and parasitoids. Provided that the female remains alive and the growth of the ambrosia fungus on which the larvae feed is satisfactory, mortality of the immature stages is likely to be very low. Most mortality is probably during the dispersal of the adults, and during gallery establishment. Adults of ambrosia beetles are predated by lizards, clerid beetles and ants as they attempt to bore into the host tree. Adults will also fail to oviposit if the ambrosia fungus fails to establish in the gallery.
Few species of parasitoid Hymenoptera have been recorded from X. dispar (Noyes, 2003) and it is unlikely that any cause major mortality. Perniphora robusta attacks ambrosia beetles (Trypodendron spp., Xyleborus spp.) throughout Europe (Balazy, 1963; Capecki, 1963; Hedqvist, 1963). Its larvae feed externally on the beetle larvae (Eichhorn and Graf, 1974). Habritys brevicornis has a very wide range of hosts which includes sphecid wasps and stratiomyiid flies, in addition to bark beetles (Noyes, 2003). Vrestovia querci was described from specimens attacking X. dispar in Quercus sp. (Noyes, 2003) and is known only from the original collection in China (Shaanxi). Eurytoma morio is a polyphagous species which attacks both scolytids and their parasitoids (Hedqvist, 1963). Schvester (1950) found a nematode of the family Allantonematidae, Parasitylenchus xylebori, in the body cavity of adult females, and found that it reduced their fecundity, but nothing more is known of the species.
Means of Movement and DispersalTop of page Natural Dispersal
Adult females fly readily, and flight is one the main means of movement and dispersal to previously uninfected areas.
In addition to the ambrosia fungus Ambrosiella hartigii, the females of ambrosia beetles often also transfer other microorganisms (Schneider-Orelli, 1913; Francke-Grosmann, 1956; Zimmermann, 1973). Natali et al. (1994) found that X. dispar females, collected in three different biotopes of hazel growing in Italy, transferred 15 bacterial species, three yeasts and three fungi. Tiberi and Ragazzi (1998) (see also Sousa, 2002) found that X. dispar collected from oak trees (Quercus) in decline, transmitted the fungi Fusarium eumartii [Nectria haematococca), F. solani and Verticillium dahliae, and suggest that the beetles can exploit the trees more easily as a result of the activity of these fungi.
Plant TradeTop of page
|Plant parts liable to carry the pest in trade/transport||Pest stages||Borne internally||Borne externally||Visibility of pest or symptoms|
|Bark||adults||Yes||Pest or symptoms usually visible to the naked eye|
|Stems (above ground)/Shoots/Trunks/Branches||adults; eggs; larvae; pupae||Yes||Pest or symptoms not visible to the naked eye but usually visible under light microscope|
|Wood||adults; eggs; larvae; pupae||Yes||Pest or symptoms not visible to the naked eye but usually visible under light microscope|
|Plant parts not known to carry the pest in trade/transport|
|Fruits (inc. pods)|
|Growing medium accompanying plants|
|True seeds (inc. grain)|
Wood PackagingTop of page
|Wood Packaging liable to carry the pest in trade/transport||Timber type||Used as packing|
|Loose wood packing material||Fresh sapwood||Yes|
|Solid wood packing material with bark||Fresh sapwood||Yes|
|Solid wood packing material without bark||Fresh sapwood||Yes|
|Wood Packaging not known to carry the pest in trade/transport|
|Processed or treated wood|
Impact SummaryTop of page
|Fisheries / aquaculture||None|
ImpactTop of page The economic damage caused by X. dispar is not easy to estimate. The beetle preferentially attacks stressed trees. Such trees might often have a chance of recovery without beetle attack.
In several countries of Europe and North America, X. dispar is sporadically a serious pest of fruit trees such as apple, apricot, peach, nectarine, pear, cherry and plum, and of hazel (Mathers, 1940; Linsley and MacLeod, 1942; Vasseur and Schvester, 1948; Schvester, 1954; Balachowsky, 1963; Postner, 1974; Viggiani, 1979; Mani and Schwaller, 1983; Hesjedal and Edland, 1988; Schick and Thines, 1988; Juillard-Condat and Perrau, 1989; Mani et al., 1990, 1992; Natali et al., 1994; Schröder, 1996; Lagowska and Winiarska, 1997; Saruhan and Tuncer, 2001). Less often, damage occurs in vineyards (Ioakimov, 1925; Russ, 1966; Mani et al., 1990, 1992). In the north-western states of America and western Canada, X. dispar is an important pest in chestnut (Castanea spp.) orchards (Bhagwandin, 1993; Kühnholz et al., 2003).
In most cases, only single trees or groups of trees are attacked and destroyed, but sometimes whole new plantings of young trees are severely damaged. This happens mostly in the second year after planting, to young plants in poor condition (Mani and Schwaller, 1983; Mani et al., 1992; Morone and Scortichini, 1998). In such cases, important economic losses can occur.
In European forests, losses due to X. dispar are sometimes important. Severe attack has been observed in young plantations of maple and oaks (Postner, 1974), of chestnut (Schvester, 1954; Bud, 1972), Chinese chestnut (Tsankov and Ganchev, 1988) and in some stands of birch, poplar and alder (Balachowsky, 1963). In Austria, sometimes massive attacks up to 4 m high have been observed both on fungus-infected and healthy trees of sycamore maple, ash, oak and cherry (Perny, 1998).
Impact: BiodiversityTop of page Mudge et al. (2001) note that the species is more abundant than native species of Scolytidae at some sites in Oregon, USA, and suggest that the ecosystem may have been permanently altered as a result of its introduction. However, it is not clear whether it has significantly reduced the abundance of the native species, or is occupying host material that would otherwise have remained unexploited.
Detection and InspectionTop of page X. dispar attack can be detected in spring by traces of fine, white sawdust trickling out of holes on the bark of trunks or larger branches. Sometimes only gum or moist spots of sap will be found with the beginning of holes.
Opening the attacked plant part reveals a ramified gallery system which is easy to distinguish from the gallery system of bark beetles.
During the flight period in spring, beetles can be caught in alcohol traps (see Biotechnical Control). The traps must be placed in spring as soon as the maximum temperature rises to 18-20°C.
Similarities to Other Species/ConditionsTop of page Postner (1974) and Alford (1984) describe the characteristics of galleries and of the biology of Xyleborinus saxesenii. This species, smaller in size than X. dispar, and with a conical, not flattened scutellum, often occurs in association with X. dispar. Keys to palearctic species of Xyleborini, including X. dispar, can be found in Balachowsky (1949), Duffy (1953), Schedl (1981) and Pfeffer (1995). Bright (1968), Wood (1982), Atkinson et al. (1990) and Vandenberg et al. (2000) have keys to nearctic species.
Prevention and ControlTop of page
Due 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.
In most areas, X. dispar is considered to be a secondary pest (Schneider-Orelli, 1913; Linsley and MacLeod, 1942; Balachowsky, 1963; Postner, 1974; Zöggeler, 1987; Schick and Thines, 1988; Juillard-Condat and Perrau, 1989; Keimer, 1990; Mani et al., 1990, 1992; Schröder, 1996; but compare Bhagwandin, 1993; Perny, 1998; Kühnholz et al., 2003). Weakened trees are especially attractive to this beetle.
For this reason all cultural measures improving the health of trees must have priority. New plantations are at risk, particularly during the first and the second spring after planting. Avoid drying of roots before and after planting. Remove and destroy infected trees and branches immediately when attack is observed, or at the latest before the beetles of the new generation leave the galleries the following spring.
No method of biological control of X. dispar exists at present. The natural enemies listed do not provide effective control, and augmentation is not likely to produce much improvement. Canganella et al. (1994) suggest that the bacteria (Pseudomonas chlororaphis and Bacillus subtilis) they found on the insect and in the galleries may represent the starting point for future research.
Schvester (1954) observed that attacked trees often produce an odour of alcohol. He explained this by the interruption or slowing down of plant sap transport and by the fermentation of this sap. Roling and Kearby (1975) showed that oak trees injected with ethanol attracted ambrosia beetles. Ethanol is apparently a good signal for a suitable host plant, especially for an ambrosia beetle cultivating a fungus in wet plant tissue (Klimetzek et al., 1986). All these observations may explain why many ambrosia beetles are attracted by alcohol traps.
In forests, window flight traps baited with ethanol are used, often in combination with pheromones, to estimate the flight periods and flight pattern of bark and ambrosia beetles (Moeck, 1970; Roling and Kearby, 1975; Annila, 1977; Schroeder and Lindelöw, 1989; Markalas and Kalapanida, 1997).
The red wing trap, baited with ethanol (Rebell rosso), has been developed in Switzerland to attract X. dispar in orchards and vineyards. It has proved to be useful in monitoring and in control systems (Mani et al., 1986, 1988, 1990, 1992). This method has become accepted in several countries (Zöggeler, 1987; Juillard-Condat and Perrau, 1989; Schröder, 1996; Lagowska and Winiarska, 1997). For other designs of trap using ethanol as a bait, see, for example, Bambara et al. (2002), Oliver and Mannion (2001) and Grégoire et al. (2003).
For monitoring, one or two traps per hectare of orchard or vineyard have to be placed in spring, when maximum temperatures rise above 17°C. In favourable weather conditions, the lure (250 ml 50% ethanol denatured with 1% toluene) has to be replaced every 2-3 days. When catches reach 20 beetles per trap per day, the risk of attack of some importance is indicated.
For control of X. dispar in an endangered orchard or vineyard, eight traps per hectare need to be placed. Such a control system will reduce the beetle population and the damage considerably.
The red wing trap attracts a variety of other insect species (especially Diptera), but only a few honey bees and known natural enemies of insect pests.
Chemical control of X. dispar is very difficult and expensive due to its protected breeding sites and its resistance to many insecticides. Therefore, sprays are only applied in exceptional cases. Compounds used previously may no longer be used. Compounds registered at present, such as carbaryl, organophosphates and pyrethroids (Viggiani, 1979; Dominik and Kinelski, 1985; Juillard-Condat and Perrau, 1989; Schröder, 1996) often give only partial control.
Insecticides are applied when the insects start flying and searching for suitable host plants (maximum temperature 18-20°C; first catches in alcohol traps) or at the latest, when the first beetles start boring entrance holes. The concentration of the insecticide is often higher than usual and the whole tree, especially the trunk and larger branches, should be sprayed thoroughly. When trap catches continue to be significant the application has to be repeated after 2-3 weeks.
Integrated Pest Management
Control of X. dispar must rely on a combination of different methods. All measures promoting plant health are essential. Attacked plant parts must be removed in time. In orchards with a risk of damage, alcohol traps should be placed for monitoring or for control. Only in exceptional cases do insecticide sprays become necessary. Eventually, it may be possible to develop the use of non-host volatiles as repellents to prevent, or at least reduce, attacks (Borden et al., 2003).
ReferencesTop of page
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Distribution MapsTop of page
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