Hubertus H. Eidmann

Orientation of the pine weevil Hylobius abietis to underground sources of host volatiles

Adults of Hylobius abietis (L.) (Coleoptera: Curculionidae) were found to locate conifer roots suitable for oviposition by utilizing host volatiles diffusing through the soil. Underground sources of host volatiles were presented to weevils in a laboratory bioassay. A cold‐trapping condensate of Scots pine, Pinus sylvestris L., and fractions of it were tested. Various fractions containing host terpenes attracted weevils in the bioassay, but the complete pine condensate caused the highest response. Ethanol was also found to be attractive. Weevils caged underground in the absence of host material did not attract weevils on the surface.

Estimating risks for spruce bark beetle (Ips typographus (L.)) damage using pheromone‐baited traps and trees

The risk for damage associated with spruce bark beetle attacks on living trees was estimated in 12 forest districts in the Nordic countries during three years. Pheromone‐baited traps and trees were used. Five groups of three traps were deployed annually on fresh spruce clear‐fellings in each district. The mean catches within districts and years ranged from 950 to 46000 beetles per trap group. The standard error averaged 15 % of the mean catch. One tree was baited annually at each of five other sites in each district. The mean number of trees colonized by Ips typographus in each district and year ranged from 0 to 5 per site. The standard error was high, averaging 44% of the mean. Inventories of tree mortality within the districts yielded values ranging from 0 to 150 killed trees per km of spruce forest edge. There was a strong linear correlation between mean catches in traps and log‐transformed tree mortality (r=0.82). The correlation between colonization success at tree‐baiting sites and tree mortality wa...

Attack rates of scolytids and composition of volatile wood constituents in healthy and mechanically weakened pine trees

The composition of volatile wood constituents in healthy (untreated) and injured (top‐cut or girdled) Scots pine trees, Pinus sylvestris L., was studied during three years using gas chromatography. The data were evaluated using PCA (principal components analysis) and PLS‐DA (projections to latent structures‐discriminant analysis), two methods for multivariate data analysis. Data from headspace analysis from the first and the third year revealed a significant difference in the composition of volatile wood constituents between untreated and top‐cut trees while GC analysis of extracts only revealed a significant difference for the first year. The higher proportions of ethanol and acetaldehyde in top‐cut trees were important in differentiating these trees from healthy ones. Differences in the monoterpene composition also seemed to be important in this respect. Untreated trees remained unattacked by the scolytid species. Hylurgops palliants (Gyll.) and Trypodendron lineatum (Oliv.) (Scolytidae) only attacked t...

Gallery initiation byTomicus piniperda (Coleoptera: Scolytidae) on scots pine trees baited with host volatiles

In a trapping experiment, wood chips from freshly cut Scots pine trees attracted flying adults of the bark beetleTomicus piniperda (L.) Healthy Scots pine trees, which usually are not attacked byT. piniperda, were baited with chips from freshly cut trees. In other experiments trees were baited with a mixture of (−)-α-pinene, (+)-3-carene, and terpinolene; the individual monoterpenes; or with ethanol alone. All baited treatments were attacked byT. piniperda. Most of the attacks resulted in short egg galleries and in larval galleries which were only a few millimeters in length. In trees from which a new generation of beetles emerged, net reproduction was well below 1.0. Unbaited control trees remained unattacked or received a few isolated attacks.

Attacks of bark- and wood-boring Coleoptera on snow-broken conifers over a two-year period.

The attacks of bark‐ and wood‐boring Coleoptera on broken conifer stems after severe snow‐breakage in early 1988 were studied in autumn 1988 and 1989. The study included twelve stands in the county of Varmland in central Sweden differing in age and edaphic conditions. The tops on the ground as well as the remaining rooted stem stumps of 94 Picea abies and 61 Pinus sylvestris were inspected. The presence of living branches on the stumps strongly influenced the incidence of insect attack. All stumps without branches were attacked during the two‐year period, whereas only a few spruce stumps with more than ten branches and no pine stumps with more than five branches were attacked. On spruce stumps, the most frequently encountered Coleoptera were all scolytids, i.e. the species Pityogenes chalcographus, Hylurgops palliatus, and the genera Polygraphus, Dryocoetes, and Trypodendron. On pine stumps, Tomicus piniperda was the most common species. Most of the spruce tops and virtually all pine tops were attacked du...

RESPONSE ON THE GROUND OF BARK BEETLE AND WEEVIL SPECIES COLONIZING CONIFER STUMPS AND ROOTS TO TERPENES AND ETHANOL

Responses of threeHylastes species,Dryocoetes autographus, and twoHylobius species to terpenes and ethanol were studied in field experiments on clear-cut forest sites in Sweden using baited ground traps.α-Pinene alone did not attract any of the six species. A terpene blend (spruce turpentine consisting mainly ofα-pinene,β-pinene, and 3-carene) attractedHylastes cunicularius, H. brunneus, andHylobius abietis in some experiments, but not in others. The attractiveness of ethanol also varied; the only species consistently attracted wasH. abietis. Baits containing both terpenes and ethanol, particularly the combination of spruce turpentine and ethanol, were attractive to all species exceptHylobius pinastri. InH. abietis, the terpene plus ethanol/ ethanol catch ratios increased during early summer. Seasonal differences in catch levels were observed inH. cunicularius andH. abietis. The addition ofα-pinene reduced the attractiveness of the combination of spruce turpentine and ethanol toH. cunicularius, H. opacus, andD. autographus. The differences in response to the volatiles between species are probably related to differences in reproductive behavior and host preferences.

Odoriferous compounds from the flowers of the conifers Picea abies, pinus sylvestris and Larix sibirica

Abstract A GC/MS analysis of the volatile constituents from the flowers of Norway Spruce, Picea abies , has been carried out. The volatile constituents of the female flowers were distinctly different from those of the male flowers and the twigs. Characteristic constituents are methyl and ethyl benzoate, methyl and ethyl salicylate, methyl and ethyl butanoate, borneol and bornyl acetate. In the scent from the male flowers we could only detect the same monoterpenes as in the twigs. In Larix sibirica methyl benzoate, methyl salicylate, borneol and bornyl acetate were detected in the female flowers and, in the female flowers of Pinus sylvestris , methyl salicylate was found.

Physical protection of conifer seedlings against pine weevil feeding

Protection of seedlings afforded by two types of coated barriers (CB) against pine weevil (Hylobius species) feeding was evaluated in field experiments in Sweden. The CB is an upright sheath surrounding a seedling and covered on the outside with a coating of polytetrafluoroethylene that hinders insects from crawling up. In experiments during 1992–1993 on four sites, protective treatments by CB applied after planting greatly reduced seedling mortality due to pine weevil feeding and increased survival over two growing seasons. Seedlings with correctly positioned CB were rarely attacked. In a large‐scale experiment during 1993–1994 on nine forest sites, protection by CB applied before planting reduced the risk of seedling mortality caused by pine weevil feeding by 93% in the first year and by 83% for both years. Seedling mortality due to Hylobius feeding in plots with CB protected seedlings was largely independent of the mortality in plots with unprotected seedlings. Pine weevil damage was less frequent on s...

Mating stimulant of the pine weevilHylobius abietis (L.)

Factors eliciting copulatory behavior in mature maleHylobius abietis were studied in the laboratory. Dead female weevils were sexually attractive, while dead mature males and pentane-extracted female weevils were not. The sexual attractiveness of dead females declined with time after death. Pentane extracts of whole female weevils or of the anterior or posterior parts of their bodies elicited a copulatory response when applied to decoys. In contrast, extracts of hindgut or frass were inactive. Juvenile males were sexually attractive for about four weeks, after which their attractiveness gradually declined. The results indicate that the mating stimulant is present on the body surface of female and juvenile male weevils, and it can be extracted with pentane.

Stockings for protection of containerized conifer seedlings against pine weevil (Hylobius abietis L.) damage

The effectiveness of a stocking, constructed of nylon and cotton netting, in protecting containerized conifer seedlings against pine weevil attack was evaluated in field tests on 37 clear‐cut reforestation areas in southern and central Sweden. The stockings significantly reduced pine weevil feeding on treated seedlings as well as seedling mortality. The protective effect of the stockings was similar to that of an insecticide (permethrin) treatment. In most experiments the survival of stocking‐enclosed seedlings was satisfactory from a practical point of view, whereas untreated control seedlings suffered heavy mortality.