The role of beetle and host volatiles in host colonization in the European oak bark beetle, Scolytus intricatus (Ratzeburg) (Col., Scolytidae)

Abstract:  To understand the role of chemical signals involved in Scolytus intricatus (Ratzeburg) (Col., Scolytidae) host colonization, the attractiveness of intact and beetle colonized host material was investigated in the field and in the laboratory. In the field, chemical signals operating at long range were investigated by means of sticky traps. In the laboratory, close-range chemical interactions were investigated with an arena olfactometer. Field experiments showed no differences in the attractiveness between infested and non-infested host material. On the contrary, laboratory experiments revealed higher attractiveness of infested host and beetle-produced frass in comparison with intact host and mechanically produced sawdust respectively. Laboratory data also disclosed the attractiveness of beetle extracts of both sexes. Our data show that: (1) host kairomones play an important role during host colonization, and that (2) S. intricatus does not use a sex-specific secondary attractant system. Differences between results of field and laboratory trials are discussed.     

Some effects of freezing temperatures on overwintering larvae of the large elm bark beetle (Scolytus scolytus)

Overwintering final instar larvae of Scolytus scolytus were tested for coldhardiness by exposure to a range of sub-zero temperatures (–7°Cto –31 °C) in a frost-gradient apparatus for 7 days. The Lt₅₀ for larvae removed from the bark (– 20.5 °C) was significantly different (P < 0.01) from the Lt50 (–18.3 °C) for larvae insulated by the bark (thickness of 7 mm ± 2 mm). Larvae with food in their digestive tract were more susceptible to freezing than the overwintering final instars which had voided their stomach contents. Duration and intensity of cold did not cause any adverse long-term effects. Most of the larvae which survived the sub-zero treatments were able to pupate or reach the adult stage. The mean supercooling point of the overwintering larvae (–30.85 °C) confirmed their cold-hardiness.     

The susceptibility of the elm bark beetle Scolytus scolytus to the DD-136 strain of Neoaplectana sp.

Adults and larve of Scolytus scolytus were highly susceptible to the DD-136 strain of Neoaplectana sp. in the laboratory.     

Significance of parasitoids in the reduction of oak bark beetle Scolytus intricatus Ratzeburg (Col., Scolytidae) in Serbia

Abstract:  As the vector of vascular fungi of the genus Ophiostoma the oak bark beetle, Scolytus intricatus , is one of the significant links in the chain of agents of oak forest decline in Serbia. It is known that the adults of this bark beetle, which develop under the bark of the trees infected by fungi of the genus Ophiostoma , transport the spores of these fungi. During the maturation feeding, the spores are transmitted to healthy tree crowns, where they germinate and cause infection. In period 1992–96 at 27 localities in Serbia, the significance of parasitoids in the reduction of this bark beetle was examined, as the intensity of spore transmission depends upon the number of oak bark beetle adults in nature. In the research of parasitoids of S. intricatus 20 species were identified in five families of Hymenoptera: Braconidae (six species), Eurytomidae (one), Pteromalidae (10), Eupelmidae (one) and Eulophidae (two). Among these parasitoids the greatest influence on the abundance of oak bark beetle was the species Ecphylus silesiacus . It was identified in 90.91% of study samples, its domination was 39.15% and the percentage of oak bark beetle parasitism was 5.66%. In addition, the species Entendon ergias , Dendrosoter protuberans and Cheiropachus quadrum were significant in reduction of S. intricatus . The average percentage of parasitism of oak bark beetle by E. ergias was 2.74%, by D. protuberans it was 2.63% and by Ch. quadrum 1.63%. The significance of other parasitoids in the reduction of oak bark beetles was low. In the study period the total parasitism of oak bark beetle varied between a minimum of 8.64% in 1992 and a maximum of 19.64% in 1996. The average for the whole study period was 14.49%.     

Biocontrol of almond bark beetle (Scolytus amygdali Geurin-Meneville, Coleoptera: Scolytidae) using Beauveria bassiana (Bals.) Vuill. (Deuteromycotina: Hyphomycetes)

AIMS: To formulate the entomopathogenic fungus Beauveria bassiana in invert emulsion, then apply it against adults of almond bark beetle (Scolytus amygdali) under laboratory and field conditions. METHODS AND RESULTS: The effect of formulated B. bassiana in invert emulsion against S. amygdali adults was shown by comparing the mortality percentage of adults exposed to the formulated fungus using a Petri dish treatment method and by field applications to infested peach trees with mortality of adults exposed to the unformulated fungus or the untreated control. Results obtained from both exposure methods have indicated that treatment of S. amygdali adults with the formulated fungus resulted in a significantly higher mean mortality percentage (P < 0.05) when compared with the treatment with the unformulated fungus or the untreated control. This mortality ranged from 81.2 to 100%, 10 days after treatment with the formulated fungus when compared with 6.7 to 49.6% mortality, 10 days after treatment with the control or the unformulated fungus, respectively. Viability of the fungus conidia in invert emulsion was assessed by calculating the germination percentage of the conidia over time. Results indicated a high storage stability shown by a small loss of germination percentage for the formulated conidia of both strains (5.8 to 8.4% over a 12-week period) vs a low storage stability shown by a high loss of germination percentage for the unformulated conidia of the same strains (58.9 to 61.0% over the same period). The presence of B. bassiana in the galleries of beetles following the treatment of infested trees was shown in the present research. CONCLUSIONS: The results obtained have demonstrated a significantly higher level of efficacy of formulated B. bassiana in invert emulsion against S. amygdali adults under laboratory and field conditions. The ingredients of invert emulsion used in the formulation of the fungus had a negligible effect on the viability of formulated conidia when compared with the unformulated. SIGNIFICANCE AND IMPACT OF THE STUDY: Results obtained in the present research are promising and may be exploited commercially to control S. amygdali adults on various species of stone fruit trees, especially peach trees. This type of biocontrol of this insect may be used as an alternative means to chemical control for management of the insect. No adverse environmental impacts of the fungus or its formulation have been observed during application.     

Laboratory studies on the fungus Verticillium lecanii, a larval pathogen of the large elm bark beetle (Scolytus scolytus)

From 1972 to 1974, estimates of the natural larval mortality (> second instar) of elm bark beetles caused by pathogenic organisms were always below 7'5 % of the beetle population. The pathogenic fungus Verticillium lecanii was frequently isolated from field-collected dead larvae, and in the laboratory all larvae were killed in 5 days when exposed to spore concentrations of 4·5 × 10⁶ spores/ml. V. lecanii begins to lose its pathogenicity after prolonged culture on artificial media. The time taken for V. lecanii to kill Scolytus scolytus larvae when exposed to a logarithmic series of spore dilutions from 9·1 × 10⁷/ml to 9·1 × 10³/ml increased with decreasing amounts of inoculum. Even at spore concentrations as low as 9·1 × 10³/ml the mortality of treated larvae was greater than that of untreated individuals. At 100% r.h. all treated larvae were killed over a temperature range of 5–30 °C; those maintained at 25 °C were killed most rapidly and those kept at 5 °C the slowest.     

Steroidal constituents and anti-inflammatory activity of the horse chestnut (Aesculus hippocastanum L.) bark

The content and the composition of sterols in the bark of the horse chestnut, Aesculus hippocastanum L., have been examined. Stigmasterol and alpha-spinasterol were, with the beta-sitosterol, the most abundant sterols. The petrol extract from bark shows anti-inflammatory activity.     

Behavioral responses of the smaller European elm bark beetle, Scolytus multistriatus, to extracts of non-host tree tissues

Crude benzene extracts of 6 non-host trees alone did not stimulate feeding responses by adults of Scolytus multistriatus (Marsh.). When combined equally with a stimulatory extract from Ulmus americana L., all of the crude non-host extracts reduced the amount of feeding which otherwise occurred. At least two of the non-hosts (Populus deltoides Bartr. and Aesculus octandra Marsh) contained positive short-range orientational stimuli, but their induction of a positive response by the insect was prevented in most treatments by associated deterrent chemicals. Thus, stimuli (deterrents and repellents) played the dominant role in eliciting the rejection of crude non-host extracts by the beetles.

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Zusammenfassung Benzol-Rohextrakte von 6 Nicht-Wirtsbäumen riefen allein bei erwachsenen Scolytus multistriatus (Marsh.) keine Fraßreaktionen hervor. Wurden sie zu gleichen Teilen mit einem stimulierenden Extrakt von Ulmus americanus L. kombiniert, so setzten alle Rohextrakte aus Nicht-Wirten die Fraßmenge herab, die sonst auftritt. Wenigstens zwei der Nicht-Wirte (Populus deltoides Bartr. und Aesculus octandra Marsh.) enthielten auf kurze Entfernung wirkende positive Reize, aber ihr Einfluß auf eine positive Reaktion des Insekts wurde bei den meisten Behandlungen durch Verbindung mit abweisenden (deterrent) Stoffen verhindert. So spielen bei der Auslösung der Ablehnung von Rohextrakten der Nicht-Wirte durch die Käfer Deterrent- und Repellent-Reize die Hauptrolle.

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Approved for publication by the Director of the Wisconsin Agricultural Experiment Station. This research was supported in part by a research grant (GB-6580) from the National Science Foundation; and from funds provided by the State of Wisconsin Department of Natural Resources.     

The DD-136 strain of Neoaplectana sp. as a potential biological control agent for the European elm bark beetle,Scolytus scolytus

When logs infected with Scolytus scolytus were sprayed with the DD-136 strain of Neoaplectana sp. in solutions of either distilled water, glycerin, or P.B.I. wetting agent, the nematodes were efficiently dispersed and entered the logs through the insect entrance holes in the bark.Logs treated with Neoaplectana sp. were found to contain a significantly higher proportion of dead, nematode-infected insects. No difference was found between the various methods of nematode application. The results indicate that Neoaplectana sp. may have a possible role in the control of S. scolytus in elm logs.     

Mitochondrial phylogenies in the light of pseudogenes and Wolbachia: re-assessment of a bark beetle dataset

Phylogenetic studies based on mtDNA become increasingly questioned because of potential pitfalls due to mitochondrial pseudogenes and mitochondrial selective sweeps. While the inclusion of nuclear markers should preferentially be considered for future studies, there is no need to abandon mtDNA as long as tests for the known mtDNA artefacts are performed. In this study we presentadditionaldata and test previous phylogeographical studies of Pityogenes chalcographus. We did not detect nuclear copies (numts) of the previously used mitochondrial markers by performing a combined long range/nested PCR of the COI gene and by an in silico analysis of the COI sequence data. This confirms the robustness of our previous phylogenetic study of Pityogenes chalcographus. Results of an in-situ hybridization of Wolbachia in Pityogenes chalcographus confirm the presence of this endosysmbiont in this species. However, we did not detect a correlation between infection status, geographical region and mtDNA haplotypes. The hybridisation data also support a previous hypothesis that infections do not result from parasitoids or parasitic nematodes, insect surface or laboratory contaminations and are hence a true infection of Pityogenes chalcographus. We conclude that the deep structure found in mitochondrial populations of Pityogenes chalcographus indeed represents the evolutionary history of European populations.     

The breakdown and decomposition of sweet chestnut (Castanea sativa mill.) and beech (Fagus sylvatica L.) leaf litter in two deciduous woodland soils

Summary Changes in the carbon, hydrogen, nitrogen and polyphenol content of chestnut and beech leaves were measured during the first year after fall.Chestnut leaves had an initial carbon, hydrogen and nitrogen content (by weight) of 48.71%, 5.56% and 0.77% respectively; beech had a similar carbon and hydrogen content (47.77% and 5.36%) but less nitrogen (0.56%).Both leaf litter types showed percentage increases in nitrogen content during the study period but only the beech showed absolute increases in nitrogen content of up to 66.7% of the initial weight present in the leaves. The percentage increases in the nitrogen content of chestnut litter were largely attributable to more rapid losses of non-nitrogenous leaf constituents while the weight of nitrogen present in the leaves remained relatively constant.The percentage carbon and hydrogen contents of the chestnut and beech litter showed changes of less than 1% throughout the year, indicating that carbohydrate losses were directly proportional to weight losses.Soil animals fed on chestnut leaves to a far greater extent than beech leaves; this difference did not appear to be directly attributable to differences between the nitrogen contents or C/N ratios of the two leaf litter species. The gross polyphenol contents of chestnut and beech litter showed an intraspecific inverse correlation with the feeding activities of soil animals on the leaves, but did not account for interspecific differences in leaf palatability since chestnut leaves were eaten when they contained higher polyphenol concentrations than beech leaves. However, there was an interspecific negative correlation between palatability and the presence of protocatechuic and gallic acids.     

Ultrastructure of sensory receptors on the antennae of Scolytus multistriatus (Marsh.)

Summary The antennae of Scolytus multistriatus were examined with light and scanning and transmitting-electron microscopy to determine the distributions, types and structures of sense organs. Four types of sensilla were found: (1) sensilla chaetica, a singly-innervated receptor; (2) sensilla basiconica, Type A, a short, thin-walled, multiple-innervated receptor; (3) sensilla basiconica, Type B, a long, thin-walled multiple-innervated receptor; and (4) sensilla trichodea, short, thick-walled, multiple-innervated receptors. The positioning of dendrite(s) with regard to pore tubules is elaborated. Evidence for lack of sensory axon fusion is presented.Approved for publication by the Director of the Research Division, College of Agricultural and Life Sciences. This research was supported in part by a research grant (GB-8756) from the National Science Foundation, and by funds from the Elm Research Institute. The authors wish to thank Dr. G. A. deZoeten and Mr. G. A. Gaard for their assistance and encouragement.     

The bark beetle Pityogenes chalcographus (L.) (Scolytidae) in living trees: reproductive success, tree mortality and interaction with Ips typographus

Abstract:  Tree-killing ability of Pityogenes chalcographus was experimentally investigated by baiting living spruce Picea abies with synthetic aggregation pheromone, thereby exposing them to beetle attack. Reproductive success was estimated by rearing beetles from stem sections taken from killed trees. The presence of Ips typographus on several killed trees allowed a comparison of reproductive success in the presence and absence of this species. Furthermore, the possibility that breeding material colonized by P. chalcographus may induce subsequent attacks by I. typographus on nearby trees was also studied. The tree killing ability of P. chalcographus was low as only 8% of the baited trees, attacked by P. chalcographus alone, were killed. Tree death was strongly related to the presence of I. typographus , which is in line with the association with aggressive wood-living fungi in this species. The reproductive success was low, with on average less than one daughter beetle produced per mother beetle. The success was significantly higher in trees also inhabited by I. typographus . Tree-parts colonized by P. chalcographus induced almost no attacks by I. typographus on nearby trees.     

Carbon isotopic composition of forest soil respiration in the decade following bark beetle and stem girdling disturbances in the Rocky Mountains

Bark beetle outbreaks are widespread in western North American forests, reducing primary productivity and transpiration, leading to forest mortality across large areas and altering ecosystem carbon cycling. Here the carbon isotope composition (δ¹³C) of soil respiration (δ_J) was monitored in the decade after disturbance for forests affected naturally by mountain pine beetle infestation and artificially by stem girdling. The seasonal mean δ_J changed along both chronosequences. We found (a) enrichment of δ_J relative to controls (<1 ‰) in near‐surface soils in the first 2 years after disturbance; (b) depletion (1‰ or no change) during years 3–7; and (c) a second period of enrichment (1–2‰) in years 8–10. Results were consistent with isotopic patterns associated with the gradual death and decomposition of rhizosphere organisms, fine roots, conifer needles and woody roots and debris over the course of a decade after mortality. Finally, δ_J was progressively more ¹³C‐depleted deeper in the soil than near the surface, while the bulk soil followed the well‐established pattern of ¹³C‐enrichment at depth. Overall, differences in δ_J between mortality classes (<1‰) and soil depths (<3‰) were smaller than variability within a class or depth over a season (up to 6‰).     

A major role for nitrification in the weathering of minerals of brown acid forest soils

Experiments employing lysimeters and a comparison of soil leachates at >‐0.03 MPa and soil solutions extracted at ‐2.5 MPa showed the importance of nitrification in the weathering of minerals of brown acid forest soils (dys‐trochrept) which are formed over large areas in temperate climates.

Mineralization of litter from plants characteristic of such soils (in particular Festuca silvatica and Abies pectinata) produces large amounts of nitric acid. This bacterial nitrification is responsible for the solubilization of Ca²⁺, Mg²⁺, and K⁺ and must be involved in the slow weathering of minerals by acidolysis and in the biogeochemical cycling of Ca²⁺, Mg²⁺, and K⁺ in these soils. Soil solutions extracted at ‐2.5 MPa reflect much more the microbial activity than the leachates from soil and provide interesting information.     

Morphology of antennal sensilla of the brown spruce longhorn beetle,Tetropium fuscum (Fabr.) (Coleoptera: Cerambycidae)

The antennal sensilla of the brown spruce longhorn beetle, Tetropium fuscum (Fabr.) (Coleoptera: Cerambycidae) were examined with particular focus on the sensilla present on the apical flagellomere. T. fuscum antennae are composed of 11 segments, namely the scape, pedicel, and nine flagellomeres. Nine types of sensilla were observed: three types of sensilla chaetica, sensilla trichodea, two types of sensilla basiconica, grooved peg sensilla, thick-walled sensilla, and Böhm bristles. Seven of these types were present on the apical flagellomere, the exceptions were sensilla chaetica type 3 and Böhm bristles. There were no significant differences in the distribution or density of sensilla present on the ninth flagellomere of males and females, except that males had significantly more sensilla chaetica type 1, which are put forward as the putative contact chemoreceptors for T. fuscum.     

Light versus pheromone-bearing wind in the control of flight direction by bark beetles, Scolytus multistriatus

ABSTRACT. A wind tunnel lit from above was used to measure the relative effectiveness of light as opposed to pheromone-bearing wind in directing the flight of male S.multistriatus. Upward flight in the tunnel was overridingly phototactic not geotactic, while horizontally upwind flight toward the pheromone source was anemotactic not chemotactic, since the pheromone concentration was uniform in the tunnel. The flight tracks of newly-emerged unfed and previously unflown beetles were preponderantly upwards and downwind; the longer the beetles had spent in flight activity beforehand, the more of them flew upwind.