Dryocoetes Autographus Research Articles

Early responses of bark and wood boring beetles to an outbreak of the hemlock looper Lambdina fiscellaria (Guenée) (Lepidoptera: Geometridae) in a boreal balsam fir forest of North America

AbstractWe investigated the early responses of bark and wood boring beetles to an extensive supply of balsam fir (Abies balsamea) trees, stressed or recently killed during an outbreak of the hemlock looper (Lambdina fiscellaria) in Quebec, Canada. The present study aimed to (i) examine beetle assemblages across all levels of defoliation and (ii) assess the relative influences of defoliation, tree mortality, stand structure and spatial context on beetle assemblages. We used three types of traps in each of 36 plots: multidirectional flight interception traps measured adult beetle flight activity within stands, trunk window traps measured visitation rates at trees and emergence traps measured beetle colonization of trees. Flight traps in nondefoliated plots allowed characterization of ‘pre‐outbreak’ beetle assemblages, which were not discernable in emergence traps because few insects colonize heathy trees. ‘Pre‐outbreak’ assemblages, characterized by a mix of polyphagous beetle species (e.g. Evodinus monticola, Dryocoetes autographus), shifted to those dominated by Trypodendron lineatum after extensive defoliation. Two Pissodes species colonized heavily defoliated trees but not dead ones. Defoliation level, conifer basal area, basal area of dead balsam firs and the extent of recently logged areas around sampling plots were positively correlated with the abundance of T. lineatum.

Occurrence of pathogens and nematodes in forest beetles from Curculionidae and Attelabidae in Bulgaria

Beetles from Curculionidae and Attelabidae collected from 14 localities (mainly in coniferous stands) in Bulgaria were investigated for the presence of pathogens and nematodes. A microsporidium belonging to genus Nosema in the fat body of Pityogenes chalcographus (prevalence: 0.9%) and the fungus Beauveria bassiana in the oak-leaf roller Attelabus nitens (prevalence: 62%) were detected for the first time. Morphological data and characteristics of Nosema sp. spores and conidia of B. bassiana are presented. Nematode species (Cryptaphelenchus diversispicularis, Parasitorhabditis subelongati and Parasitylenchus dispar), and specimens belonging to other ten nematode genera were found (Bovianema, Bursaphelenchus, Cryptaphelenchus, Neoparasitylenchus, Parasitylenchus, Parasitaphelenchus, Panagrolaimus, Parasitorhabditis, Prothallonema and Sulphuretylenchus). Their prevalences varied from 17.4% to 90%. Nine of the host beetles (Dryocoetes autographus, Ips sexdentatus, I. acuminatus, Orthotomicus laricis, O. erosus, Pityogenes quadridens, P. conjunctus, Hylurgus ligniperda and Taphrorychus villifrons) are reported as vectors of Bursaphelenchus sp.

Mites Trichouropoda and Uroobovella spp. (Uropodoidea) phoretic on bark beetles (Scolytinae): a comparison from a declining mountain spruce forest in Central Europe

ABSTRACTMites of the genera Trichouropoda and Uroobovella are characteristic associates of bark beetles which act as agents of their dispersal in many types of forest ecosystems worldwide. We compared the phoretic assemblages of Trichouropoda and Uroobovella mites on six species of bark beetle associated with Norway spruce (Picea abies (L.) Karsten), namely: Dryocoetes autographus Ratzeburg, Hylastes cunicularius Erichson, Hylurgops palliatus (Gyllenhal), Ips typographus (Linnaeus), Pityogenes chalcographus (Linnaeus) and Polygraphus poligraphus (Linnaeus). Bark beetles were caught at random in non-baited flight-interception traps set in the shrub layer of a declining mountain spruce forest in the Tatra Mountains, West Carpathians, Central Europe. Over four years of a bark beetle outbreak, a total of six species of mites and 12 phoretic associations between mites and beetles were recorded. A newly documented host association includes that of Trichouropoda pecinai Hirschmann & Wiśniewski with H. palliatus. The most frequently recorded mite-beetle associations were: T. pecinai with H. cunicularius, Trichouropoda obscura (Koch) with H. palliatus, Trichouropoda polytricha (Vitzthum) with P. chalcographus and I. typographus and Uroobovella vinicolora (Vitzthum) with D. autographus. The results suggest that most of the recorded mite species have distinct bark beetle dispersants and that niche partitioning in these dispersants may be reflected by the observed mite–host associations.

Overlooked subterranean saproxylic beetle diversity in clear-cut stumps and its implications for stump extraction

Stump extraction (which include removal of coarse roots) will reduce the available habitat for insects breeding in dead wood (saproxylic species). The root-living diversity is largely unknown which is unsatisfactory as 68% of the wood harvested at stump extraction is root wood. We compared the diversity of saproxylic beetles in Norway spruce, Picea abies, coarse roots with that in the above-ground part of the same stumps. Five below-ground (root) and eight above-ground (stump) samples were collected from early-decay stumps at each of twelve Swedish clear-cuts. In total 8314 saproxylic beetles of 60 species were reared from the 156 wood samples. The estimated species richness in roots (47 species) was 51% of that in stumps (93). When root and stump samples were pooled the total estimate was 116 species. The phylogenetic diversity (average taxonomic distinctness) in individual roots was only 63% of that in stumps. Species composition differed between substrate types, and only 28% of the species were common to both substrates. Most root samples were numerically dominated by Dryocoetes autographus (33% of the samples) or Hylobius abietis (10%). Most stump samples were dominated by Crypturgus spp. (66%) or Rhagium inquisitor (19%). Of the 17 most abundant species, five were associated with roots and two of those used roots exclusively. Ten species were associated with stumps. We conclude that the root-living beetles constitute an important part of the stump/root assemblage and should not be overlooked when the effects of stump harvest on biodiversity is evaluated.

Non-target Bark Beetles in <i>Ips duplicatus</i> (Sahlberg) Pheromone Traps Baited with Host Volatiles

Response of several non-target bark beetles (Coleoptera: Curculionidae, Scolytinae) to different combinations of the northern spruce bark beetle’s synthetic pheromone with the monoterpenes (-)-alpha-pinene and (+)-limonene has been studied in choice experiments in the field with flight barrier traps. The experiments were organized in four Norway spruce stands (40-50 years old) outside its natural area, in the north-east of Romania, where Ips duplicatus (Sahlberg) populations had reached an epidemical level. Each experiment had five treatments randomly replicated in six blocks within each experimental plot. Four non-target bark beetle species were captured together with Ips duplicatus: I. typographus (L.) (2611 beetles), Pityogenes chalcographus (L.) (184 beetles), Hylastes cunicularius Erichson (107 beetles) and Dryocoetes autographus (Ratzeburg) (24 beetles), representing 1.77%, 0.13%, 0.07% and 0.02% respectively of total captures. Beetles of I. typographus were attracted by synthetic pheromone blend of I. duplicatus and have intensified their response in the presence of (-)-alpha-pinene or a combination between (-)-alpha-pinene and (+)-limonene, but the other species have been captured in the traps accidentally. The positive response of I. typographus to the present formulation of I. duplicatus pheromone suggests the possibility to use the pheromone dispensers for both species in the same traps when mass-trapping is the main goal, but new studies should clarify the real effects of putting together pheromone dispensers of I. typographus or P. chalcographus with those of I. duplicatus.

The Evaluation of the Bark Beetles Populations on Spruce Logging Debris

Today, when somebody is talking about bark beetles management, there are two different approaches. The first one includes bark beetles in the category of pests and the second one includes bark beetles in the category of insects with important ecologic role in forest. From our point of view, up to particular limits, both approaches remain valid. Thus, in our research raise the problem of bark beetles population level into logging debris, which remains in the forest after clear-cutting. In our research, we started with the hypothesis that in logging debris a high number of bark beetles can multiply sufficient to install after that in neighbors standing trees. From our samples resulted seven bark beetles species as follows: Ips typographus , Ips amitinus , Ips acuminatus , Pityogenes chalcographus , Dryocoetes autographus , Hylurgops palliatus , Hylurgops glabratus . The most numerous were I. typographus (43%), P. chalcographus (40%), and H. palliatus (9%). The preferences for the thickness of logging debris had just P. chalcographus and H. palliatus . All the rest of the species preferred in equal mode thick or thin logging debris. Regarding the felling date of trees, we can affirm that cutting of trees early in spring may limit the beetles spreading. About logging debris management, our results show the necessity of their removal from forest and capitalization, because they are hosts for many bark beetles.

The occurrence of bark beetles on cut Norway spruce branches left in managed stands relative to the foliage and bark area of the branch

This study addresses the relationships between the foliage and bark area of Norway spruce (Picea abies) branches left in the forest after managing large timber: the densities of infestation by Pityogenes chalcographus, Pityophthorus pityographus and Dryocoetes autographus; and the reproductive efficiency of P. chalcographus. Based on the models developed in this study, a positive correlation was found between the foliage area of spruce branches and the densities infested by P. chalcographus and D. autographus, though a higher negative correlation was found in relation to the size of the branch bark area (BA) and the infestation densities. A negative correlation for the branch BA was also found on P. pityographus. This result shows that the desiccation of branches affects the infestation densities of bark beetles. In contrast, the size of the branch BA was positively correlated with the reproductive efficiency of P. chalcographus, with higher reproductive efficiency on the branches from the outer layer of the pile than on disorderly scattered branches on the ground.

Effects of trap height on captures of arboreal insects in pine stands of northeastern United States of America

AbstractKnowledge of the effects of variables that can influence trapping results should help to optimise efforts in exotic species detection and other surveys. Two vertical trap placements (understorey, canopy) were tested to determine influence of these two heights on captures of Scolytinae (Coleoptera: Curculionidae), Cerambycidae (Coleoptera), and Siricidae (Hymenoptera) using semiochemical-baited multiple-funnel traps. Traps were baited with α-pinene, ethanol, ipsdienol, and ipsenol. A total of 8463 insects from 65 species and one genus were captured during the study. Average species richness, species diversity, abundance, number of unique species, and expected diversity were higher in understorey compared with canopy traps. Jaccard (0.94 ± 0.05) and Sørensen abundance (0.97 ± 0.03) similarity indices suggested highly similar communities sampled at the two trap heights.Dendroctonus valensLeConte,Dryocoetes autographusRatzeburg,Hylastes opacusErichson,Orthotomicus caelatus(Eichhoff),Gnathotrichus materiarius(Fitch),Asemum striatum(Linnaeus),Monochamus scutellatus scutellatus(Say),Rhagium inquisitor(Linnaeus), andXylotrechus sagitattus sagitattus(Germar) were more abundant in understorey traps. In contrast,Ips pini(Say),Pityogenes hopkinsiSwaine,Monochamus carolinensis(Olivier),Acmaeops proteus(Kirby), andAstylopsis sexgutatta(Say) were more abundant in canopy traps. The common practice of trapping in the understorey may be optimal for sampling arboreal insects as part of survey efforts. However, additional species may be found by trapping at other vertical placements.

DNA barcoding of bark and ambrosia beetles reveals excessive NUMTs and consistent east‐west divergence across Palearctic forests

A comprehensive DNA barcoding library is very useful for rapid identification and detection of invasive pest species. We tested the performance of species identification in the economically most damaging group of wood-boring insects - the bark and ambrosia beetles - with particular focus on broad geographical sampling across the boreal Palearctic forests. Neighbour-joining and Bayesian analyses of cytochrome oxidase I (COI) sequences from 151 species in 40 genera revealed high congruence between morphology-based identification and sequence clusters. Inconsistencies with morphological identifications included the discovery of a likely cryptic Nearctic species of Dryocoetes autographus, the possible hybrid origin of shared mitochondrial haplotypes in Pityophthorus micrographus and P.pityographus, and a possible paraphyletic Xyleborinus saxeseni. The first record of Orthotomicus suturalis in North America was confirmed by DNA barcoding. The mitochondrial data also revealed consistent divergence across the Palearctic or Holarctic, confirmed in part by data from the large ribosomal subunit (28S). Some populations had considerable variation in the mitochondrial barcoding marker, but were invariant in the nuclear ribosomal marker. These findings must be viewed in light of the high number of nuclear insertions of mitochondrial DNA (NUMTs) detected in eight bark beetle species, suggesting the possible presence of additional cryptic NUMTs. The occurrence of paralogous COI copies, hybridization or cryptic speciation demands a stronger focus on data quality assessment in the construction of DNA barcoding databases.

Cambioxylophagous fauna developing on logging residues of blue spruce (Picea pungens Engelmann)

Cutting down 20- to 30-years-old trees of blue spruce (Picea pungens Engelm.) (October, May) and cross-cutting them to sections of different volume (0.5–75 dm3) under conditions of half-shade × open area resulted in a potential food offer for cambiophages. Ips amitinus (Eichh.) and Pityogenes chalcographus (L.) reached the higher frequency of occurrence on sections placed in the open area than in half-shade and on stems felled in the autumn season than in the spring season. Dryocoetes autographus (Ratz.) was markedly profiled on sections in half-shade with the gradual desiccation of phloem. P. chalcographus preferring open areas occurred on branches being accompanied by Cryphalus abietis (Ratz.), which attacked branches located in half-shade. On stems of sections from both autumn and spring felling, one generation of I. amitinus developed, however, on autumn sections, the 2<sup>nd</sup> generation developed unsuccessfully on the original nutritive material. P. chalcographus completed the development of one generation on stems and branches from autumn felling. On the spring material, the invasion was delayed and a part of wintering larvae did not complete their development. Logging residues of P. pungens were available for the development of I. amitinus and P. chalcographus during one growing season only.

Utilization of Carbohydrates by Beauveria Bassiana Isolates Obtained from Forest Pests

Carbohydrate utilization profiles of ten isolates of the entomopathogenic fungus Beauveria bassiana (Bals.-Criv.) Vuillemin were studied and compared to assist in determining their phenotypic characterization. Isolates were obtained in pure cultures from dead individuals of several forest pests collected from different regions in Bulgaria. Studies on utilization profiles were based on the acidification of twenty carbohydrates. The results indicate that sucrose, maltose and trehalose were assimilated at a high degree compared to esculin, arabinose and dul- citol. According to the results of a cluster analysis of the carbohydrate utilization profiles, the B. bassiana isolates were divided into two larger groupings. All isolates in the first larger cluster were obtained from the coleopteran insects - Stenomax aeneus, Ips typographus, I. sexdentatus and Dryocoetes autographus. Isolates from the other cluster were obtained from the lepidopteran larvae of Thaumetopoea pityocampa and Lymantria dispar, and from an adult of the coleopteran species Hylurgops palliatus. We determined that each B. bassiana isolate exhibited a different and specific carbohydrate utilization profile but differences at the p-level < 0.05 were significant among some of them. The most distinguishable was the isolate 560Bb obtained from T. pityocampa. Differences between the isolate 560Bb and the other nine B. bassiana isolates were highly significant at the p-level < 0.005. Isolate 433Bb obtained from a dead adult of I. typogra- phus was significantly different from five of the studied isolates at the p-level < 0.05.

Species Composition, Seasonal Activity, and Semiochemical Response of Native and Exotic Bark and Ambrosia Beetles (Coleoptera: Curculionidae: Scolytinae) in Northeastern Ohio

In 2007, we surveyed the alien and endemic scolytine (bark and ambrosia beetles) fauna of northeastern Ohio, and for the most abundant species, we characterized their seasonal activity and response to three semiochemical baits. In total ,5,339 scolytine beetles represented by 47 species and 29 genera were caught in Lindgren funnel traps. Three species constituted 57% of the total catch, including Xylosandrus germanus (Blandford), Tomicus piniperda (L.), and Dryocoetes autographus (Ratzeburg). Of the total captured, 32% of the species and approximately 60% of the individuals were exotic, suggesting that exotic species numerically dominate the scolytine fauna in some urban areas. More native and exotic species were caught in traps baited with ethanol alone than in traps baited with other lures. However, significantly more individuals, especially of T. piniperda, D. autographus, Gnathotrichus materiarius (Fitch), and Ips grandicollis (Eichhoff), and species were caught in traps baited with ethanol plus alpha-pinene than in traps baited with ethanol alone or the exotic Ips lure. This suggests that among these baits, the ethanol plus alpha-pinene baits may be useful in maximizing scolytine beetle catches of these species within this region. Species diversity and richness for both native and exotic beetles was greatest in traps baited with ethanol alone. The period of peak trap capture varied depending upon species: X. germanus was most abundant in traps in mid-May and early-August; T. piniperda in mid-May; D. autographus in early June, mid-July, and mid-September; Anisandrus sayi Hopkins and G. materiarius in mid-May, mid-July, and early September; and I. grandicollis in early April, mid-July, and late September.

Naturally-occurring entomopathogenic fungi on three bark beetle species (Coleoptera: Curculionidae) in Bulgaria

Bark beetles (Coleoptera: Curculionidae: Scolytinae) belong to one of the most damaging groups of forest insects and the activity of their natural enemies - pathogens, parasitoids, parasites or predators suppressing their population density, is of great importance. Biodiversity of entomopathogenic fungi on bark beetles in Bulgaria has been investigated sporadically. The aim of this preliminary study was to find, identify and study morphological characteristics of fungal entomopathogens naturally-occurring in populations of three curculionid species - Ips sexdentatus Boern, Ips typographus (L.) and Dryocoetes autographus (Ratz.). Dead pest adults were found under the bark of Pinus sylvestris and Picea abies trees collected from forests in the Maleshevska and Vitosha Mountains. Fungal pathogens were isolated into pure cultures on SDAY (Sabouraud dextrose agar with yeast extract) and were identified based on morphological characteristics both on the host and in a culture. Morphological characteristics of the isolates were studied by phenotypic methods. The fungal isolates obtained from dead adults of Ips sexdentatus, Ips typographus and D. autographus were found to belong to the species Beauveria bassiana (Bals. - Criv.) Vuillemin, Beauveria brongniartii (Saccardo) Petch and Isaria farinosa (Holmsk.) Fries (anamorph Ascomycota, Sordariomycetes: Hypocreales, Cordycipitaceae). Morphological traits of the isolates are described.

Landing Patterns of Phloem- and Wood-feeding Coleoptera on Black Spruce of Different Physiological and Decay States

We examined landing patterns of phloeophagous and xylophagous Coleoptera among trees and snags of different physiological and decay states in a pure open-canopy black spruce stand in boreal Canada to study prelanding host selection mechanisms in the absence of nonhost volatiles. Sticky traps were used to capture insects landing on high- and low-density natural snags (i.e., wood density), girdled trees, living trees, and stovepipe controls. Patterns were generally weak, with high within-group variability in species composition and landing rates. Within-group variability differed between groups, with highest variations in living trees and recent snags. Despite this evidence of frequent landing on suboptimal or inappropriate hosts, affinities were detected in most common taxa. Cerambycidae showed preferences for girdled trees. Common species of Scolytinae showed divergent preferences, because Crypturgus borealis Swaine and Dryocoetes autographus (Ratzeburg) were captured more often on high-density natural snags, Polygraphus rufipennis (Kirby) on girdled trees, and Orthotomicus latidens (LeConte) on living trees. These observed landing patterns are broadly consistent with current knowledge on the ecology of these species. Although preferences, and thus prelanding assessment of hosts based on volatiles, were detected in several species, the numerous landings observed on inappropriate hosts suggest that random landing at close range may be as common in pure stands as what was previously observed in mixed stands.

Quantitative Association of Bark Beetles with Pitch Canker Fungus and Effects of Verbenone on Their Semiochemical Communication in Monterey Pine Forests in Northern Spain

The association between 11 species of bark beetles (Coleoptera: Scolytinae) and one weevil (Coleoptera: Entiminae) with the pitch canker fungus, Fusarium circinatum Nirenberg and O'Donnell, was determined by crushing beetles on selective medium and histone H3 gene sequencing. Pityophthorus pubescens (Marsham) (25.00%), Hylurgops palliatus (Gyllenhal) (11.96%), Ips sexdentatus (Börner) (8.57%), Hypothenemus eruditus Westwood (7.89%), Hylastes attenuatus Erichson (7.40%), and Orthotomicus erosus (Wollaston) (2.73%) were found to carry the inoculum. In addition, the root weevil Brachyderes incanus L. (14.28%) had the second highest frequency of occurrence of the fungus. The responses of the insects to a range of verbenone doses were tested in field bioassays using funnel traps. Catches of P. pubescens, a species colonizing branch tips of live trees, were significantly reduced in a log-linear dose-dependent relationship. Catches of I. sexdentatus, an opportunistic species normally attacking fresh dead host material, were also gradually reduced with increasing verbenone dose. Catches of Tomicus piniperda L., O. erosus, Dryocoetes autographus (Ratzeburg), H. eruditus, Xyleborus dryographus (Ratzeburg), Hylastes ater (Paykull), Hylurgus ligniperda (F.), H. attenuatus, and B. incanus were not significantly affected by verbenone. The effects of verbenone were consistent with differences in host-age preference. Semiochemical disruption by verbenone in P. pubescens and I. sexdentatus could represent an integrated pest management strategy for the prevention of the spread of pitch canker disease between different stands. However, several species associated with F. circinatum were unaffected by verbenone, not supporting this compound for prevention of the establishment of potential vectors in Northern Spain.

Conservation-oriented manipulations of coarse woody debris affect its value as habitat for spruce-infesting bark and ambrosia beetles (Coleoptera: Scolytinae) in northern Sweden

Many species of Scolytinae are pests in boreal forests, so factors that affect their abundance are of great interest to forestry. Using emergence and window traps we examined the effects of stand type and substrate characteristics on the abundance of spruce-infesting Scolytinae in northern Sweden. Several species of Scolytinae (Crypturgus subcribrosus, Hylastes cunicularius, Hylurgops palliatus, Pityogenes chalcographus, Polygraphus punctifrons) were captured in greater numbers on snags than on untreated logs. Log exposure also had a significant effect on some species, H. palliatus and Trypodendron lineatum were more abundant in window traps on artificially shaded logs than on naturally shaded or untreated logs. Significantly fewer Dryocoetes autographus, H. palliatus,Hylurgops glabratus, andH. cunicularius were captured on burned logs than on untreated logs. Stand type clearly affected several species, P. chalcographus emerged in greater numbers on clearcuts than in mature managed and old-growth stands, and D. autographus,H. glabratus, and T. lineatum showed the opposite pattern. Historical records suggest that pest outbreaks are rare in northern Sweden; however, improved knowledge of the habitat preferences of potential pest species in this region will allow us to take the necessary precautions against outbreaks, whilst leaving sufficient dead wood to support intact saproxylic assemblages.

Epitypification of Ophiostoma galeiforme and Phylogeny of Species in the O. galeiforme Complex

Ophiostoma galeiforme was described first in 1951 from Larix kaempferi in Scotland, where it was found to be associated with the bark beetles Hy-lurgops palliatus, Dryocoetes autographus, and the ambrosia beetle Trypodendron lineatum. The taxonomy of this fungus has been uncertain because of a lack of sexual structures on the type specimen and contamination of a preserved ex-type culture. The aim of this study was to clarify application of the species name, O. galeiforme, by designating an epitype and to consider phylogenetic relationships of the species. Nineteen isolates resembling O. galeiforme from different parts of the world were used, including collections from Pinus sylvestris infested with Tomicus pi-niperda in Scotland and the contaminated ex-type culture. Morphological characteristics of isolates from Sweden, South Africa, Scotland, Chile and Aus-tria corresponded well with those originally described for O. galeiforme, and an isolate from Scotland is designated as the epitype. A detailed description is provided. Results of interfertility tests showed that O. galeiforme is heterothallic. Analysis of ITS rDNA sequences showed that the isolates representing O. galeiforme were distinct from three morphologically similar isolates from the USA and Mexico, which probably represent an undescribed taxon.

Epitypification of Ophiostoma galeiforme and phylogeny of species in the O. galeiforme complex

Ophiostoma galeiforme was described first in 1951 from Larix kaempferi in Scotland, where it was found to be associated with the bark beetles Hy-lurgops palliatus, Dryocoetes autographus, and the ambrosia beetle Trypodendron lineatum. The taxonomy of this fungus has been uncertain because of a lack of sexual structures on the type specimen and contamination of a preserved ex-type culture. The aim of this study was to clarify application of the species name, O. galeiforme, by designating an epitype and to consider phylogenetic relationships of the species. Nineteen isolates resembling O. galeiforme from different parts of the world were used, including collections from Pinus sylvestris infested with Tomicus pi-niperda in Scotland and the contaminated ex-type culture. Morphological characteristics of isolates from Sweden, South Africa, Scotland, Chile and Aus-tria corresponded well with those originally described for O. galeiforme, and an isolate from Scotland is designated as the epitype. A detailed description is provided. Results of interfertility tests showed that O. galeiforme is heterothallic. Analysis of ITS rDNA sequences showed that the isolates representing O. galeiforme were distinct from three morphologically similar isolates from the USA and Mexico, which probably represent an undescribed taxon.

Phloeophagous and predaceous insects responding to synthetic pheromones of bark beetles inhabiting white spruce stands in the Great Lakes region.

Tree killing and saprophytic bark beetles exert important ecological and economic roles in North American spruce forests. Chemical signaling among bark beetles, and responses by associate insects such as predators and competitors, have significant effects on the population dynamics and ecology of this community. Synthetic pheromones of primary (tree killing) and secondary (saprophytic) bark beetle species and blank controls were tested using multiple funnel and lower stem flight traps in white spruce forests in Wisconsin, Michigan, and Minnesota. Six phloeophagous and four predaceous species were collected with significant attraction by the bark beetles Dryocoetes affaber, Dryocoetes autographus, and Polygraphus rufipennis, and the predatory checkered beetles (Coleoptera: Cleridae) Thanasimus dubius and Enoclerus nigrifrons. In general, trap catches to synthetic lures resembled the species composition obtained by felling trees and collecting emerging beetles in a companion study, although several species showed differing trends. Some cross attraction occurred among bark beetles and between bark beetles and predatory beetles. For example, P. rufipennis was abundant in traps baited with Dryocoetes spp. pheromones. Thanasimus dubius and E. nigrifrons were collected in significant numbers in traps baited with the pheromone of the spruce beetle (Dendroctonus rufipennis), frontalin plus a-pinene. This is a new observation for E. nigrifrons. Attraction of T. dubius to the pheromones of at least three bark beetle species in the Great Lakes region, as well as to several southern and western species, reflects its role as a habitat specialist and feeding generalist. Several other important predators and competitors commonly obtained in pine forests in this region were not obtained in these spruce stands, either in response to synthetic pheromones of spruce colonizing beetles, or in host material colonized by these beetles. Potential differences in predator prey dynamics between spruce and pine ecosystems in the Great Lakes region are discussed.

Distribution of bark insects in ?island? plantations of spruce (Picea abies (L.) Karst.) in subarctic Norway

Eleven isolated plantations of Norway spruce Picea abies (L.) Karst, in Troms county, northern Norway, were examined for bark insects in summers 1990 and 1991. Field-infested bolts from controlled fellings were reared in laboratory to complement field-investigations. Results are compared to records made from the same plantations 1974–78. Eight scolytid species, two curculionids and two cerambycids were found inhabiting spruce in 1990–91. Dryocoetes autographus was found in ten, and Tetropium castaneum in 9 plantations. Hylastes cunicularius has apparently expanded its distribution since 1978. One plantation had no bark insects confined to spruce, except old galleries of Pityogenes chalcographus. No new immigrants to the region were found, but one curculionid species may have become extinct. Reproduction of Dryocoetes autographus and Tetropium castaneum was studied in the laboratory. D. autographus bred consecutive generations from the same bolt, whereas T. castaneum displayed varying generation time, partly within the same bolt. This enhances their viability in plantations where felling activity is low. Several scolytid species widely distributed elsewhere in naturally spruce-forested areas in Scandinavia north of the Arctic circle are still absent in Troms, including all the smallest species. It is suggested that the success of colonizers in unpredictable climates depends on both dispersal capabilities (larger species have a higher dispersal power than the smallest species), life cycle flexibility and versatility in habitat requirements. It is concluded that only species with certain properties have established in the plantations, i.e. the immigration and colonization is not stochastic.