Hylurgops palliatus
(lesser spruce shoot beetle)

H. palliatus is distributed in coniferous and mixed forests throughout the whole palaearctic region from England to Sakhalin and Japan. It is common in northern and central Europe, and Siberia.

H. palliatus is typically a secondary species with broad host ranges (e.g. Escherich, 1923; Stark, 1952; Krivolutskaja, 1983; Eidmann, 1987; Pfeffer, 1995). The preferred host tree is Picea abies, but it also occurs on Pinus sylvestris, Pinus cembra, Pinus strobus, Pinus nigra, Larix europea and Abies pectinata [Abies alba] (Freude et al., 1981), and rarely on Cedrus (Koch, 1992).

Insect attack on logs from trees of 22 exotic conifer species in the genera Picea, Abies, Larix and Pseudotsuga was studied in Sweden. H. palliatus was among the most frequently found insect species (Eidmann, 1987). In southern Bohemia, Czech Republic observations were made in 11 species of Picea, Abies, Pinus, Larix, Pseudotsuga and Juniperus. H. palliatus was determined in trap logs from P. abies, Picea pungens, P. sylvestris and Pinus jeffreyi (Zumr, 1992).

Physiology and Phenology

The phenology and life cycle of H. palliatus were studied in Finland and Denmark (Nuorteva, 1956; Subansence, 1971). Ozols (1975), Lekander et al. (1977) and Rudnev and Vasechko (1988) provide data on its development in different regions.

Trees are infested in early spring. Studies were carried out in two forest areas in Denmark (Zealand and South Jutland) to determine the emergence dates and flight periods of H. palliatus. It was shown that the overwintered adults began to fly in April, when the maximum temperature reached approximately 6°C, and the peak of activity occurred in late April when the maximum temperatures were approximately 15-25°C (Subansence, 1971). Flight activity declined in June. The adults of the new generation emerged between July and November/December, with a peak in August. These adults flew little and overwintered near the sites in which they had developed. There was only one generation a year.

In Latvia, the swarming starts in mid-April (Ozols, 1975). In Finland it takes place in early May and the first eggs were observed in the mid-May (Nuorteva, 1956). In general, all development stages have been observed during quite a long period in the summer.

Reproductive Biology

The biology and ecology of H. palliatus is briefly reviewed by Escherich (1923), Stark (1952), Postner (1974), Lekander et al. (1977), Rudnev and Vasechko (1988), and Ehnström and Axelsson (2002). Wood and Bright (1992) gave several references relating to the biology, habitats and taxonomy of H. palliatus.

H. palliatus is a monogamous species. In central Scandinavia, H. palliatus flies from the end of April to the beginning of May (Lekander et al., 1977). The immature beetles seek the under-side of timber and branches cut in the winter and preferably those that are lying directly in contact with the ground. They make irregular galleries in the bark. Some weeks later the now mature beetles leave these galleries and look for suitable material in which to breed. The larvae mine in all directions without any evident pattern and they eventually consume the entire phloem in localized areas of heavy infestation. They pupate in late July and the new generation emerges in August. Generally, H. palliatus hibernates in the bark in association with the gallery systems but more occasionally in stump roots or litter. Generally, there is one generation annually. In the Ukraine, a sister generation may be produced or a second generation occurs, and hibernation as a larva is also possible (Rudnev and Vasechko, 1988).

The egg galleries are usually longitudinal and 2-5 cm long. According to Nuorteva (1956), the mean number of eggs in egg galleries was 37; the biggest number of eggs was observed in the relatively short egg galleries: 2.7 cm - 63 eggs, 2.2 cm - 62 eggs and 2.2 cm - 39 eggs.

Environmental Requirements

H. palliatus is a typically secondary species (Escherich, 1923). It generally reproduces in dead or dying trees. Chararas (1959) studied osmotic pressures in the bark, wood and needles of branches of Pinus sylvestris and Picea abies. For both species, low pressures were associated with heavy attacks by Scolytidae. Measurements on a large number of samples showed that H. palliatus attacked branches only when bark pressures were in the range 3-5 atm, i.e. in dying trees.

H. palliatus infests the bases and roots of dying trees and stumps. It prefers logs cut during the autumn of the previous year to newly cut logs (Schroeder, 1991). This type of older breeding material may release relatively high amounts of ethanol produced in deteriorating tree tissue, whereas monoterpenes are probably released in lower amounts compared with the amounts released from newly felled or broken trees. Schroeder (1992) also studied the field response of H. palliatus to the attractant ethanol in combination with volatile wood constituents released from the non-host tree species Populus tremula and Betula pendula. The attraction of the species decreased when aspen or birch wood was added to the ethanol bait.

The sections close to the roots and parts of bark lying on the soil surface or partially covered with soil were attacked by H. palliatus. It occurs mainly on the under-side of timber, branches and other logging waste. Also the lower part (up to about 2 m) of standing, dying or dead trees, and occasionally stumps and roots, will be attacked. It seems to prefer high humidity in the bark and often occurs with Trypodendron lineatum (striped ambrosia beetle) (Ozols, 1975; Lekander et al., 1977; Koch, 1992; Jakus, 1998).

In Sweden, the attacks of bark beetles on broken conifer stems after severe snow-breakage in early 1988 were studied in autumn 1988 and 1989 (Schroeder and Eidmann, 1993). H. palliatus was frequently encountered on spruce and pine stumps in the second year following snow-breakage, whereas on spruce stumps it also occurred in the first year (Schroeder and Eidmann, 1993).

The attack density and breeding success of the bark beetles and the abundance of their predators were studied at forest-clearcut edges in southern Finland on Picea abies (Norway spruce) (Peltonen and Heliövaara, 1999). Attack densities of H. palliatus increased markedly towards the forest interior. The breeding success of H. palliatus was increased with increasing distance from the stand edge.

Attacks of bark and wood-boring beetles on mechanically created high stumps of P. abies were studied in central Sweden. H. palliatus was among the most frequently encountered species on the stumps. A negative relationship was found between stump diameter and H. palliatus occupancy (Schroeder et al., 1999).

Associations

Wingfield and Gibbs (1991) studied the blue-stain fungi associated with H. palliatus. Isolations for blue-stain fungi were made from Hylastes ater, Hylastes opacus, H. palliatus and Tomicus piniperda trapped in Pinus sylvestris billets. Five Leptographium spp. including one of unknown identity and two, apparently undescribed Graphium spp., were isolated. Leptographium procerum, Leptographium serpens [Ophiostoma serpens] and Leptographium wingfieldii were recorded for the first time in the UK. Leptographium lundbergii had previously been found in this country.

A dark stain penetrating only shallowly into the sap wood develops round the gallery and is most often caused by Ophiostoma penicillatum (Lekander et al., 1977).

In Germany, a new species of the hyphomycete genus Phialocephala, Phialocephala trigonospora, was isolated from conifericolous bark beetles (Dryocoetes autographus, H. palliatus, Ips typographus and Orthotomicus laricis) and their galleries in the bark of Pinus sylvestris and P. abies (Kirschner and Oberwinkler, 1998).

During a survey of fungi associated with bark beetles (Crypturgus cinereus, Crypturgus pusillus, D. autographus, H. palliatus, I. typographus, Pityogenes chalcographus and Trypodendron lineatum) in Germany, an undescribed species of Ophiostoma was isolated. This differs from the other species of the genus by having pigmented, aseptate, convergent ostiolar hyphae; cucullate, sheathed ascospores; and is a Hyalorhinocladiella anamorph. The species is described as Ophiostoma neglectum. It is rarely associated with primary bark beetles but often associated with secondary bark beetles mainly infesting P. abies (Kirschner and Oberwinkler, 1999b).

Diplocladium gregarium was described almost 100 years ago. It was recent rediscovered from bark beetle (C. pusillus, D. autographus, H. palliatus, I. typographus and Orthotomicus laricis) galleries in the bark of P. abies and Pinus sylvestris in Germany. The fungus was redescribed and a new genus (Cylindrocarpostylus) was proposed to accommodate it (Kirschner and Oberwinkler, 1999a).

A previously unknown heterobasidiomycetous fungus was isolated from the galleries of H. palliatus, collected from P. abies in Germany. It is described as Atractocolax pulvinatus gen. et sp. nov. (Kirschner et al., 1999).

Several species of bark beetles may carry dauer larvae of nematodes. H. palliatus proved to be a vector of dauer larvae of Bursaphelenchus poligraphi, Bursaphelenchus eggersi and Bursaphelenchus sexdentati in Germany (Braasch et al., 1999).

Kakulia et al. (1973) studied the nematode fauna of H. palliatus in the Former Republic of Georgia. Parasitorhabditis palliati, Cryptaphelenchus cryptus, B. eggersi, Mikoletzkya palliati, Panagrolaimus fuchsi and Cephalobus persegnis were found in H. palliatus and its frass on Picea orientalis in the Borzhomy and Khashuri districts of Georgia.

Crypturgus cinereus was found in the galleries of H. palliatus (Michalski and Mazur, 1999).

In Finland, H. palliatus was among the most abundant bark beetle species in a dead Norway spruce stand flooded by beavers (Castor canadensis) (Saarenmaa, 1978).

The natural enemies of H. palliatus were investigated by several authors (e.g. Nuorteva, 1956; Kolomiets and Bogdanova, 1980; Nikitski, 1980; Õunap, 1992, 2001; Grodzki, 1997). In Finland, 25 species of Coleoptera and some larvae of Medetera flies, and three species of chalcidids were found in the galleries of H. palliatus (Nuorteva, 1956). Õunap (1992, 2001) studied the natural enemies of bark beetles, and listed 46 species of predators and parasitoids associated with H. palliatus in Estonia. Twenty-nine species of predators and parasitoids of H. palliatus were found in Siberia, Russia (Kolomiets and Bogdanova, 1980). Grodzki (1997) studied the parasitoids, predators and commensals of the cambiophagous insects on Norway spruce in the Sudety Mountains of Poland. Michalski and Mazur (1999) provide a wide list of natural enemies for Poland; organisms other than insects (e.g. acari) are also listed.

Nuorteva (1959) discusses systematics, biology, and bark beetle associations (for example) of five Medetera species found in Finland. From the mean numbers of Medetera larvae found per breeding gallery of H. palliatus (1.75), beetle larvae destroyed by fly larvae in feeding tests (7) and eggs of H. palliatus per breeding gallery (38), it is estimated that Medetera larvae destroyed approximately one-third of the H. palliatus larvae.

In a spruce forest near Aarau, Switzerland. web-building spiders were observed as predators of H. palliatus (Moor and Nyffeler, 1983). A small erigonid spider, Troxochrus nasutus was observed feeding on H. palliatus and Pityogenes chalcographus bark beetles (Moor and Nyffeler, 1984).

Protozoa as pathogens of some species of bark beetles were studied in Germany (Purrini, 1978, 1980). A list of the 16 species of Protozoa that are known as pathogenic to scolytids is given, together with their hosts, spore size and the names of their collectors. H. palliatus was found to be infected by Nosema cf. typographi in Upper Bavaria (Purrini, 1978). Trophozoites and cysts of Malamoeba scolyti n.sp. (Amoebidae, Rhizopoda, Protozoa) were found in the Malpighian tubules of 14% of H. palliatus collected from spruce stands in Lower Saxony, Germany (Purrini, 1980). Only the pupae and adult beetles were infected.

Traps baited with host volatiles and ethanol would be used for detection of H. palliatus. Chemical communication systems in secondary bark beetles, including H. palliatus, and their attraction to host volatiles, have been investigated by several researchers (e.g. Perttunen, 1957; Kohnle, 1985; Schroeder, 1988, 1991; Schroeder and Lindelöw, 1989; Lindelöw et al., 1992; Byers, 1992).

Perttunen (1957) investigated the reactions of H. palliatus to different concentrations of alpha-pinene in the laboratory. H. palliatus was strongly repelled by the higher and slightly by the lower concentration.

Scolytids normally living in spruce, or in spruce as well as in pine, were mostly attracted to stored spruce wood. Even though fresh wood attracted many H. palliatus, stored wood was generally the more attractive host material for this species (Lindelöw et al., 1992). Chemical analyses of the wood samples revealed differences in the composition of volatile constituents between stored and fresh spruce wood. Samples from stored tree stems showed a considerable increase in the relative amounts of two volatile constituents during storage. These constituents have been identified as ethanol and acetaldehyde using gas chromatography (Sjödin et al., 1989). Ethanol was found in different relative amounts in injured trees but not in healthy trees. Ethanol and acetaldehyde are also produced in stressed trees (Kimmerer and Kozlowski, 1982).

H. palliatus was attracted to traps containing ethanol as a bait and spruce resin acted synergistically (Kohnle, 1985). Schroeder (1988) also found that H. palliatus was attracted by ethanol. Combinations of alpha-pinene and ethanol attracted high numbers of H. palliatus and the catches increased with increasing release rates of ethanol.

According to Volz (1988), who studied host selection in the bark beetles under field conditions, H. palliatus preferred flight barrier traps baited with ethanol and oleoresin from their favoured host, Picea abies, compared to traps baited with ethanol and various monoterpenes. However, the replacement of host-specific oleoresin with beta-pinene and the pine characteristic terpinolene enhanced trap catches of the species. The response of H. palliatus increased with myrtenol, but decreased with transverbenol.

Byers (1992) confirmed that a monoterpene mix containing (±)-a-pinene, (+)-3-carene and terpinolene plus ethanol was significantly more attractive to H. palliatus than ethanol alone. The baiting of pipe traps with a series of short-chain alcohols (methanol to hexanol) showed that ethanol was greatly preferred by H. palliatus but sometimes it was attracted to propanol. No insects were caught on butanol, pentanol, hexanol, ethylene glycol or unbaited pipe traps (Byers, 1992).

Schroeder and Lindelöw (1989) studied the attraction of scolytids and associated beetles by using different absolute amounts and proportions of alpha-pinene and ethanol in field experiments with flight barrier traps. Traps baited with both alpha-pinene alone and ethanol alone caught significantly higher numbers than unbaited traps of H. palliatus. However, H. palliatus was not attracted as strongly to alpha-pinene alone as Tomicus piniperda was but it was synergistically attracted to combinations of alpha-pinene and ethanol (Schroeder, 1991). Combinations of alpha-pinene and ethanol resulted in a synergistically increased attraction of this species. The effect of synergism was strongest when the release rate of ethanol was ten times higher than that of alpha-pinene.

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.

H. palliatus is typically a secondary species and does not need any control measures.