Prepupal diapause and instar IV developmental rates of the spruce beetle, Dendroctonus rufipennis (Coleoptera: Curculionidae, Scolytinae)

The spruce beetle, Dendroctonus rufipennis (Kirby), is an important mortality agent of native spruces throughout North America. The life-cycle duration of this species varies from 1 to 3 years depending temperature. The univoltine cycle (one generation per year) is thought to maximize outbreak risk and accelerate host mortality in established outbreaks. Prepupal diapause is associated with the semivoltine cycle (one generation per 2 years) and we investigated thermal conditions that result in diapause induction. Preliminary experiments used respirometry in an attempt to distinguish the diapause state of experimental insects but the technique was apparently confounded by low respiration before and during pupation, regardless of diapause status. Therefore, diapause induction was deduced using developmental delays. The observed developmental response was not a “switch”, with developmental delay either present or absent, but instead varied continuously. We found that temperatures <15 °C from instar III through mid-instar IV were associated with developmental delays beyond that expected from cool temperatures. Moreover, the duration of exposure to cool temperatures was important in determining the degree of developmental delay. Small, if any, delays were observed if the cumulative exposure to <15 °C was <20 d whereas >40 d cumulative exposure was associated with distinct developmental suppression. Intermediate exposure to cool temperatures resulted in minor developmental delays. We used our results to parameterize a maximum likelihood estimation model of temperature-dependent instar IV developmental rates, including the effect of diapause. This model can be included as part of a spruce beetle phenology model for predicting population dynamics.     

MCH released in a novel pheromone dispenser prevents spruce beetle,Dendroctonus rufipennis (Coleoptera: Scolytidae), attacks in south-central Alaska

Field tests of 3-methyl-2-cyclohexen-1-one (MCH), the antiaggregation pheromone of the spruce beetle, Dendroctonus rufipennis Kirby, were conducted in south-central Alaska in stands of Lutz spruce, Picea x lutzii Little, and Sitka spruce, P. sitchensis (Bong.) Carr. The deployment of MCH in a novel releaser significantly reduced trap catches and spruce beetle attacks on standing live spruce by 96 and 87%, respectively. The results of this study demonstrate the first successful field test of MCH in Alaska for the prevention of spruce beetle attacks on standing, live spruce.     

Isolation and virulence of entomopathogenic fungi against the great spruce bark beetle,Dendroctonus micans (Kugelann) (Coleoptera: Scolytidae)

Twelve fungal strains including Lecanicillium muscarium (Petch.) Zare and Gams, Isaria farinosa (Holmsk.) Fr., Fusarium sp., Beauveria bassiana Sensu Lato and Beauveria sp. were isolated from larvae and adults of D. micans. In addition, virulence of these isolates against this pest was determined. Conidia suspensions of 1×10⁶ conidia mL^–1 were applied to larvae and adults. The highest mortality and mycosis for larvae were obtained from isolate ARSEF 9271 (Beauveria bassiana) with 90% mortality and mycosis within 10 days. ARSEF 9271 also produced 93% mortality and mycosis in adults. On the other hand, the highest mortality and mycosis for adults were obtained with isolate ARSEF 9272 (Beauveria sp.), with 100% mortality and 80% mycosis within 10 days. These results indicate that isolates ARSEF 9271 and ARSEF 9272 seem to be the most promising potential fungal biocontrol agents against D. micans.     

Phylogeography of spruce beetles (Dendroctonus rufipennis Kirby) (Curculionidae: Scolytinae) in North America

Tree-feeding insects that are widespread in north temperate regions are excellent models for studying how past glaciations have impacted differentiation and speciation. We used mitochondrial DNA (mtDNA) sequences and allele frequencies at nine microsatellite loci to examine genetic population structure across the current range of the spruce beetle (Dendroctonus rufipennis), an economically important insect in North America. Two major haplotype groups occur across northern North America, from Newfoundland to Alaska, on white spruce (Picea glauca), and a third distinctive haplotype group occurs throughout the Rocky Mountains on Engelmann spruce (Picea engelmannii). The two mtDNA lineages found in northern populations are 3-4% divergent from each other and from the lineages found in the Rocky Mountains. Analyses of microsatellite data also suggest the existence of major population groupings associated with different geographical regions. In the Pacific Northwest, concordant contact zones for genetically distinct populations of spruce beetles and their principal hosts appear to reflect recent secondary contact. Although we could detect no evidence of historical mtDNA gene flow between allopatric population groups, patterns of variation in the Pacific Northwest suggest recent hybridization and introgression. Together with the pollen record for spruce, they also suggest that beetles have spread from at least three glacial refugia. A minimum estimate of divergence time between the Rocky Mountain and northern populations was 1.7 Myr (million years), presumably reflecting the combined effects of isolation during multiple glacial cycles.     

The effect of larval aggregation behaviour on larval growth of the spruce bark beetle Dendroctonus micans

1. The great spruce bark beetle Dendroctonus micans is a primary pest of spruce in Europe. It is unusual among Eurasian scolytids in that apparently healthy trees are attacked by solitary adults, but larvae feed en masse , in response to a larval aggregation pheromone.
2. The effect of brood size on larval growth was determined in experiments on detached bark, logs and living trees. A positive relationship was found between brood size and larval growth in experiments started with either eggs or larvae up to fifth instar. The relationship appeared to be independent of the effects of both preformed and induced defences in bark.
3. No evidence was found to support the hypothesis that larvae feeding in groups spend a greater proportion of time feeding. Addition of resin to egg chambers in detached bark pieces resulted in high mortality of first-instar larvae. A possible role for larval aggregation in minimizing the effects of host defences is discussed.     

Arthropods and nematodes co-occurring with the eastern larch beetle,Dendroctonus simplex [Col.: Scolytidae], in Newfoundland

Fifty-four species of insects, 5 of spiders, 5 of mites, 1 harvestman and 1 nematode co-occurred with the eastern larch beetle,Dendroctonus simplex LeConte, on tamarack,Larix laricina (Du Roi) K. Koch, at 2 localities in Newfoundland. The most abundant predators were the flyMedetera gaspensis Bickel and the beetleRhizophagus dimidiatus Mannerheim and the most abundant parasitoids were the HymenopteraSpathius canadensis Ashmead,Rhopalicus tutela (Walker) andRoptrocerus xylophagorum (Ratzburg).D. simplex is recorded as a new host for 9 predator and 3 parasitoid species.      

Scramble competition in the southern pine beetle, Dendroctonus frontalis

Abstract .1. The nature of intraspecific competition was investigated in the southern pine beetle, Dendroctonus frontalis , a highly destructive pest of pine forests in the southern U.S.A. Data were analysed from an observational study of naturally-attacked trees, and from field experiments where attack density was manipulated by adding different numbers of beetles to caged trees.
2. The effect of attack density on gallery construction, oviposition, brood survival, and the overall rate of increase was examined, and a flexible model of intraspecific competition used to classify the type of competition (contest or scramble) at different points in the life cycle.
3. The results of these analyses suggest that contest competition occurs during gallery construction and oviposition, in accord with previous work on D. frontalis . Strong scramble competition occurs later on in development, however, and the overall competitive process is better characterized as scramble competition, similar to other bark beetles. Trees with attack densities sufficiently high to produce significant competition are common in the field.     

The first study on the bacterial flora of the european spruce bark beetle, Dendroctonus micans (Coleoptera: Scolytidae)

The European spruce bark beetle, Dendroctonus micans Kugelann (Coleoptera, Scolytidae), is one of the most serious pests of oriental spruce (Picea orientalis L.) in Turkey. In this study, we investigated bacterial flora of D. micans collected from different populations of the forests of Eastern Black Sea Region of Turkey from 2002 to 2004. Seven different bacteria were isolated from healthy, diseased and dead specimens based on the color of colony and morphology. According to morphological, physiological and biochemical properties, metobolic enyzme profile by BIOLOG microtiter plate system, and total cellular fatty acid profile by Microbial Identification System (MIS), isolates were identified as Micrococcus luteus, Bacillus thuringiensis subsp. morrisoni, Serratia grimesii, Enterobacter cloaceae, Enterobacter intermedius, Streptococcus sp. and Pseudomonas putida. This is the first study on the bacterial flora of D. micans.     

The role of lignin as a defence against the spruce bark beetle Dendroctonus micans: effect on larvae and adults

Summary The role of lignin as a physical defence against Dendroctonus micans was investigated in laboratory feeding experiments. The effect of lignin is dose-dependent, reducing larval survival, growth rate, and weight, as well as affecting gallery construction. Adults lay fewer eggs in lignified bark and also tend to construct abnormal galleries. The distribution of lignin in trees suggests a role in defence against bark beetles that feed in the thicker bark on the lower bole.     

Modeling cold tolerance in the mountain pine beetle, Dendroctonus ponderosae

Cold-induced mortality is a key factor driving mountain pine beetle, Dendroctonus ponderosae, population dynamics. In this species, the supercooling point (SCP) is representative of mortality induced by acute cold exposure. Mountain pine beetle SCP and associated cold-induced mortality fluctuate throughout a generation, with the highest SCPs prior to and following winter. Using observed SCPs of field-collected D. ponderosae larvae throughout the developmental season and associated phloem temperatures, we developed a mechanistic model that describes the SCP distribution of a population as a function of daily changes in the temperature-dependent processes leading to gain and loss of cold tolerance. It is based on the changing proportion of individuals in three states: (1) a non cold-hardened, feeding state, (2) an intermediate state in which insects have ceased feeding, voided their gut content and eliminated as many ice-nucleating agents as possible from the body, and (3) a fully cold-hardened state where insects have accumulated a maximum concentration of cryoprotectants (e.g. glycerol). Shifts in the proportion of individuals in each state occur in response to the driving variables influencing the opposite rates of gain and loss of cold hardening. The level of cold-induced mortality predicted by the model and its relation to extreme winter temperature is in good agreement with a range of field and laboratory observations. Our model predicts that cold tolerance of D. ponderosae varies within a season, among seasons, and among geographic locations depending on local climate. This variability is an emergent property of the model, and has important implications for understanding the insect's response to seasonal fluctuations in temperature, as well as population response to climate change. Because cold-induced mortality is but one of several major influences of climate on D. ponderosae population dynamics, we suggest that this model be integrated with others simulating the insect's biology.     

Oxidation products of pinene in the bark beetle,Dendroctonus frontalis

Southern pine beetles were collected as they emerged from infested pine bolts and exposed in Petri dishes to α- and β-pinene for 20 hr. Changes in the volatile contents of the beetles' hindguts were detected by gas chromatography, and previously unidentified components were characterized by mass, i.r., and n.m.r. spectroscopy. A prominent compound in hindguts of both sexes before and after treatment was identified as myrtenol, and a less conspicuous, male-specific compound proved to be myrtenal. Upon exposure to α-pinene, males produced cis- and trans-verbenol, and 4-methyl-2-pentanol was found in both sexes. Compounds present after treatment with β-pinene vapour were identified as trans-pinocarveol in both sexes, and pinocarvone in the males.     

Successful colonization, reproduction, and new generation emergence in live interior hybrid spruce Picea engelmannii×glauca by mountain pine beetle Dendroctonus ponderosae

1 Although mountain pine beetle Dendroctonus ponderosae Hopkins are able to utilize most available Pinus spp. as hosts, successful colonization and reproduction in other hosts within the Pinaceae is rare.
2 We observed successful reproduction of mountain pine beetle and emergence of new generation adults from interior hybrid spruce Picea engelmannii × glauca and compared a number of parameters related to colonization and reproductive success in spruce with nearby lodgepole pine Pinus contorta infested by mountain pine beetle.
3 The results obtained indicate that reduced competition in spruce allowed mountain pine beetle parents that survived the colonization process to produce more offspring per pair than in more heavily-infested nearby pine.
4 We also conducted an experiment in which 20 spruce and 20 lodgepole pines were baited with the aggregation pheromone of mountain pine beetle. Nineteen pines (95%) and eight spruce (40%) were attacked by mountain pine beetle, with eight (40%) and three (15%) mass-attacked, respectively.
5 Successful attacks on nonhost trees during extreme epidemics may be one mechanism by which host shifts and subsequent speciation events have occurred in Dendroctonus spp. bark beetles.     

Genetic relationships among Leptographium terebrantis and the mycangial fungi of three western Dendroctonus bark beetles

Morphology, mitochondrial DNA (mtDNA) restriction fragment polymorphisms (RFLPs) and nuclear DNA (nDNA) fingerprinting were used to clarify relationships among the morphologically similar Ophiostoma and Leptographium species associated with mycangia of three Dendroctonus bark beetles (Ophiostoma clavigerum associated with both D. ponderosae and D. jeffreyi, and L. pyrinum associated with D. adjunctus), as well as a closely related nonmycangial bark beetle associate (L. terebrantis). Most isolates of O. clavigerum form long (40-70 μm), septate conidia, while all isolates of L. terebrantis and L. pyrinum form conidia less than 17.0 μm in length. The conidia of L. pyrinum are pyriform, with truncate bases, while the conidia of the other species form only slightly truncate bases. Conidial masses of L. terebrantis are creamy yellow, while the conidial masses of the other species are white. Nuclear DNA fingerprints resulting from probing PstI restrictions with the oligonucleotide probe (CAC)(5) and HaeIII and MspI restrictions of mtDNA, exhibited three major clusters. In the dendrogram developed from mtDNA RFLPs, the L. pyrinum isolates formed one cluster, while the majority of O. clavigerum isolates, including all D. jeffreyi isolates, formed another. A third cluster was composed of all L. terebrantis isolates, as well as several O. clavigerum isolates from D. ponderosae. The inclusion of some O. clavigerum isolates in the L. terebrantis cluster suggests that horizontal transfer of mtDNA has occurred among these fungi. The nDNA dendrogram also exhibited three clusters, and most isolates of L. pyrinum, L. terebrantis and O. clavigerum grouped separately; however, one isolate of O. clavigerum grouped with the L. terebrantis isolates, while one isolate of L. terebrantis grouped with O. clavigerum. No genetic markers were found that distinguished between O. clavigerum associated with D. ponderosae and O. clavigerum associated with D. jeffreyi. Ophiostoma clavigerum might be a recently diverged morphological variant of L. terebrantis, with special adaptations for grazing by young adults of D. jeffreyi and D. ponderosae. The anamorph of O. clavigerum, Graphiocladiella clavigerum, is transferred to Leptographium.     

Target-specific PCR primers can detect and differentiate ophiostomatoid fungi from microbial communities associated with the mountain pine beetle Dendroctonus ponderosae

The aim of this study was to develop DNA probes that could identify the major fungal species associated with mountain pine beetles (MPB). The beetles are closely associated with fungal species that include ophiostomatoid fungi that can be difficult to differentiate morphologically. The most frequently isolated associates are the pine pathogens Grosmannia clavigera and Leptographium longiclavatum, the less pathogenic Ophiostoma montium, and an undescribed Ceratocystiopsis species (Cop. sp.). Because growing, isolating and extracting DNA from fungi vectored by MPB can be time and labour intensive, we designed three rDNA primer sets that specifically amplify short rDNA amplicons from O. montium, Cop. sp. and the pine Leptographium clade. We also designed two primer sets on a gene of unknown function that can differentiate G. clavigera and L. longiclavatum. We tested the primers on 76 fungal isolates that included MPB associates. The primers reliably identified their targets from DNA obtained from pure fungal cultures, pulverized beetles, beetle galleries, and tree phloem inoculated with G. clavigera. The primers will facilitate large-scale work on the ecology of the MPB-fungal-lodgepole pine ecosystem, as well as phytosanitary/quarantine sample screening.     

Effect of associated fungi on the immunocompetence of red turpentine beetle larvae,Dendroctonus valens (Coleoptera: Curculionidae: Scolytinae)

Abstract Dendroctonus–fungus symbioses are often considered as the ideal model systems to study the development and maintenance of ectosymbioses, and diverse interactions, including antagonism, commensalism and mutualism, have been documented between these organisms. The red turpentine beetle, Dendroctonus valens LeConte (Coleoptera: Curculionidae: Scolytinae) is a pine‐killing invasive beetle in northern China. Fungi species Ophiostoma minus, Leptographium sinoprocerum, L. terebrantis and L. procerum were associated with this bark beetle. Antagonistic interactions between D. valens and its associated fungi, such as O. minus and L. sinoprocerum, have been demonstrated, but the underlying causes of this phenomenon are unknown. Here, we first found the two tested fungi species retarded the net weight gain of D. valens larvae after completing 3‐day feeding on their media. Furthermore, we provide direct evidence indicating the effect of associated fungi on the immunocompetence of D. valens larvae to explain the documented antagonism. Our results showed that the activity of phenoloxidase and total phenoloxidase in D. valens larvae were significantly upregulated by two strains of associated fungi, O. minus and L. sinoprocerum as compared with the controls. The phenoloxidase ratio increased significantly in the larvae which had fed for 3 days on media inoculated with O. minus. Because insect immune defenses are costly to be deployed, these results could be explored as one of the underlying mechanisms of the documented antagonism.     

Attraction of the southern pine beetle, Dendroctonus frontalis, to pheromone components of the western pine beetle, Dendroctonus brevicomis (Coleoptera: Curculionidae: Scolytinae), in an allopatric zone

Subtle differences in pheromone components of sympatric species should be attractive only to the producing species and unattractive or repellent to the nonproducing species, and thereby maintain reproductive isolation and reduce competition between species. Bark beetles Dendroctonus brevicomis and D. frontalis (Coleoptera: Curculionidae) are known to have common pheromone components, except for exo-brevicomin, which is produced by D. brevicomis. We predicted that D. frontalis would not respond to exo-brevicomin outside of the zone of sympatry with D. brevicomis. We conducted a field experiment to determine the effect of exo-brevicomin on attraction of D. frontalis and associated species in Mississippi. We determined whether D. frontalis pheromone production differed inside and outside the sympatric zone and compared the pheromone profiles with D. brevicomis within the sympatric zone. Trapping studies revealed that D. frontalis can perceive and respond positively to exo-brevicomin, an aggregation pheromone of a sympatric congener (D. brevicomis), at locations hundreds of kilometers outside the sympatric zone. Qualitative pheromone profiles showed that both species emit similar pheromone components: frontalin, endo-brevicomin, exo-brevicomin, trans-verbenol, verbenone, and myrtenol. Although not previously reported, D. frontalis males from Arizona produced exo-brevicomin. The predator Thanasimus dubius did not discriminate traps baited with exo-brevicomin and was most attracted to traps with frontalin. Hylastes beetles were significantly attracted to traps baited with exo-brevicomin in combination with other compounds. Our results raise new practical and evolutionary questions on the role of exo-brevicomin in the behavioral ecology of D. frontalis. The addition of exo-brevicomin to the current lure might increase the efficiency of trapping programs in the southeastern United States.     

Trapping, parasitism, and poisoning of nematodes by fungi

Naturally occurring toxins and nematode-destroying fungi are the two major factors controlling soil nematode populations. Nematode-destroying fungi fall into two groups - hyphal forms, producing traps which capture nematodes, and endoparasitic forms, both common in natural soils. Nematode-destroying fungi have been used in attempts to control levels of pathogenic nematodes in agricultural soils with limited success.     

Cost-effectiveness analysis of options within an Integrated Crop Management regime against great spruce bark beetle, Dendroctonus micans, Kug. (Coleoptera: Scolytidae)

1 Great spruce bark beetle Dendroctonus micans (Kug.) (Coleoptera: Scolytidae) has been subject to an Integrated Crop Management (ICM) regime in Great Britain since its first discovery in 1982. The elements of the ICM approach are sanitation felling of the initial infestations, restriction on movement of potentially infested conifers to prevent spread to uninfested parts of the country and biological control through rearing and release of the specific predatory beetle Rhizophagus grandis Gyll. (Coleoptera: Rhizophagidae). Such a programme carries costs that have to be evaluated against the benefits to the ICM strategy. 2 This paper presents a cost-effectiveness analysis of three options – (i) continue with the current policy of restriction on movement of infested timber and use of the imported predator R. grandis, (ii) do nothing (i.e. drop all attempts to reduce the spread of D. micans), or, (iii) introduce a new east–west Dendroctonus Micans Control Area (DMCA) to define the management area. Assumptions on rates of mortality and natural spread were based on research into D. micans in Britain’s spruce forests. 3 Appraisal indicated that the current policy was the most cost-effective, even when subject to sensitivity analysis to test the limits of the assumptions included in the models. It is concluded that the current policy should remain in force.