Cover Caption

A red tuepentine beetle adult (Dendroctonus valens LeConte) on a Chinese pine bolt. Dendroctonus‐fungus symbioses are often considered as the ideal model systems to study the development and maintenance of ectosymbioses. The body surface of both adults and larvae carry their associated fungi. In this study, those fungi were isolated to study the direct effect of associated fungi on the immunocompetence of the beetle to explain the documented antagonism based on the principles of ecological immunology (see pages 579‐584). Photo by Runzhi Zhang.     

Ophiostomatoid fungi (Ascomycota) associated with <Emphasis Type="Italic">Pinus tabuliformis</Emphasis> infested by <Emphasis Type="Italic">Dendroctonus valens</Emphasis> (Coleoptera) in northern China and an assessment of their pathogenicity on mature trees

Dendroctonus valens is an invasive pest in coniferous forests of northern China. It was suspected of being responsible for the death of more than three million Pinus tabuliformis trees. The present study sought to identify the ophiostomatoid fungi associated with D. valens in northern China and understand the possible role of these fungi in the pine decline. On the basis of morphology, physiology, mating compatibility and phylogenetic analyses of multiple DNA sequences, seven species of ophiostomatoid fungi were isolated from and around D. valens galleries: Leptographium alethinum, Grosmannia koreana (teleomorph of L. koreanum), L. procerum, L. sinoprocerum, L. truncatum, Pesotum aureum and P. pini. All have been recorded for the first time in China. Among them, the occurrence of the dominant species L. procerum is positively linked to attack intensities of D. valens. The pathogenicity of four species (L. koreanum, L. procerum, L. sinoprocerum and L. truncatum) was tested on mature P. tabuliformis trees by stem inoculation. All inoculated strains caused significant necrotic lesions on the inner bark. However, L. koreanum and L. truncatum induced more extensive lesions than L. procerum and L. sinoprocerum. Their association with D. valens and the P. tabuliformis decline is discussed.     

Strong indirect interactions of Tarsonemus mites (Acarina: Tarsonemidae) and Dendroctonus frontalis (Coleoptera: Scolytidae)

Phoretic mites of bark beetles are classic examples of commensal ectosymbionts. However, many such mites appear to have mutualisms with fungi that could themselves interact with beetles. We tested for indirect effects of phoretic mites on Dendroctonus frontalis, which attacks and kills pine trees in North America. Tarsonemus mites are known to carry ascospores of Ophiostoma minus, which tends to outcompete the mutualistic fungi carried by D. frontalis. Experimental additions and removals of mites from beetles demonstrated that Tarsonemus propagate O. minus in beetle oviposition galleries. Furthermore, the abundance of Tarsonemus and O. minus tended to covary in nature. These results verified a strong mutualism between Tarsonemus and O. minus. Results also indicated that O. minus is an antagonist of D. frontalis: beetle larvae seldom survived in the presence of O. minus (compared to 83% survival elsewhere). Apparently, this is an indirect result of O. minus outcompeting the two species of mycangial fungi that are critical to beetle nutrition. Thus, Tarsonemus mites close a loop of species interactions that includes a commensalism (mites and beetles), a mutualism (mites and O. minus), asymmetric competition (O. minus and mycangial fungi), and another mutualism (mycangial fungi and beetles). This interaction system produces negative feedback that could contribute to the endogenous population dynamics of D. frontalis. Reproductive rate of Tarsonemus was more temperature‐sensitive than beetle generation time (which constrains the time for mite reproduction within a tree). This differential temperature sensitivity produces a narrow range of temperatures (centred at 27°C) in which mite reproduction per D. frontalis generation can attain its maximum of 100 mites/beetle. Consequently, seasonal oscillations in temperature are predicted to produce oscillations in the D. frontalis community, and climatic differences between regions could influence the community to dampen or exacerbate the cyclical outbreak dynamics of D. frontalis.     

Immunocompetence of the red turpentine beetle, Dendroctonus valens LeConte (Coleoptera: Curculionidae, Scolytinae): Variation between developmental stages and sexes in populations in China

Immune defense imposes fitness costs as well as benefits, so organisms should optimize, not maximize, their immune function through their life cycle. We investigated this issue in the red turpentine beetle, Dendroctonus valens LeConte (Coleoptera: Curculionidae, Scolytinae), which is a pine-killing invasive beetle in China, though it is usually considered as a secondary pest in its native range of North America. We hypothesized that pathogen pressure may affect these beetles differently throughout their life history. We measured the insect's immunocompetence throughout life, determining encapsulation ability and phenoloxidase activity in larval stages, pupae and adults. Pupae had the highest encapsulation ability, but encapsulation was not different between final instar larvae and adults. Phenoloxidase (PO) activity was highest in final instar larvae and pupae, followed by the second instar larvae and adults. Total phenoloxidase activity increased significantly from the second instar larval stage to pupae, and then decreased in adults. Although the second instar larvae had the lowest phenoloxidase activity, more than 90% of total PO existed in the hemolymph in the form of the active enzyme, as compared with pupae, in which over 60% of PO occurred as a proenzyme. Both active PO and total PO were much higher in females than in males, though no significant differences were detected between the encapsulation ability of male and female adults. This result suggests the existence of a sexual dimorphism of immunocompetence in D. valens adults. Variations in immunocompetence across developmental stages suggest that D. valens adopts diverse investment strategies in immunocompetence during different stages. Potential reasons for variation in immunocompetence among developmental stages and between the sexes of D. valens are discussed.     

Antagonisms, mutualisms and commensalisms affect outbreak dynamics of the southern pine beetle

Feedback from community interactions involving mutualisms are a rarely explored mechanism for generating complex population dynamics. We examined the effects of two linked mutualisms on the population dynamics of a beetle that exhibits outbreak dynamics. One mutualism involves an obligate association between the bark beetle, Dendroctonus frontalis and two mycangial fungi. The second mutualism involves Tarsonemus mites that are phoretic on D. frontalis (“commensal”), and a blue-staining fungus, Ophiostoma minus. The presence of O. minus reduces beetle larval survival (“antagonistic”) by outcompeting beetle-mutualistic fungi within trees yet supports mite populations by acting as a nutritional mutualist. These linked interactions potentially create an interaction system with the form of an endogenous negative feedback loop. We address four hypotheses: (1) Direct negative feedback: Beetles directly increase the abundance of O. minus, which reduces per capita reproduction of beetles. (2) Indirect negative feedback: Beetles indirectly increase mite abundance, which increases O. minus, which decreases beetle reproduction. (3) The effect of O. minus on beetles depends on mites, but mite abundance is independent of beetle abundance. (4) The effect of O. minus on beetles is independent of beetle and mite abundance. High Tarsonemus and O. minus abundances were strongly correlated with the decline and eventual local extinction of beetle populations. Manipulation experiments revealed strong negative effects of O. minus on beetles, but falsified the hypothesis that horizontal transmission of O. minus generates negative feedback. Surveys of beetle populations revealed that reproductive rates of Tarsonemus, O. minus, and beetles covaried in a manner consistent with strong indirect interactions between organisms. Co-occurrence of mutualisms embedded within a community may have stabilizing effects if both mutualisms limit each other. However, delays and/or non-linearities in the interaction systems may result in large population fluctuations. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Population genetics and symbiont assemblages support opposing invasion scenarios for the red turpentine beetle (Dendroctonus valens)

Exotic forest insects and their symbionts pose an increasing threat to forest health. This is apparently true for the red turpentine beetle (Dendroctonus valens), which was unintentionally introduced to China, where the beetle has killed millions of healthy native pine trees. Previous population genetics studies that used cytochrome oxidase I as a marker concluded that the source of D. valens in China was western North America. In contrast, surveys of fungi associated with D. valens demonstrated that more fungal species are shared between China and eastern North America than between China and western North America, suggesting that the source population of D. valens could be eastern North America. In this study, we used microsatellite markers to determine population structure of D. valens in North America as well as the source population of the beetle in China. The analyses revealed that four genetically distinct populations (herein named the West, Central, Northeast and Mexico) represent the native range of D. valens. Clustering analyses and a simulation‐based approximate Bayesian computation (ABC) approach supported the hypothesis that western North America is the source of the invasive D. valens population. This study provides a demonstration of non‐congruence between patterns inferred by studies on population genetics and symbiont assemblages in an invasive bark beetle.     

Bacterial Community and Nitrogen Fixation in the Red Turpentine Beetle, <Emphasis Type="Italic">Dendroctonus valens</Emphasis> LeConte (Coleoptera: Curculionidae: Scolytinae)

The red turpentine beetle, Dendroctonus valens LeConte (Coleoptera: Curculionidae: Scolytinae), colonizes all pines species within its native range throughout North and Central America. Recently, this species was accidentally introduced to China, where it has caused severe damage in pine forests. It belongs to a group of beetles that spend most of their lives between the tree bark and sapwood, where it feeds on phloem: a poor substrate with very low nutritional value of nitrogen and toxic properties due to its high content of secondary defensive compounds. The aim of this study was to characterize the bacterial community of the D. valens gut by culture-dependent and -independent methods. Polymerase chain reaction denaturing gradient gel electrophoresis and ribosomal gene library analyses revealed that species diversity in the D. valens gut was relatively low, containing between six and 17 bacterial species. The bacterial community associated with larvae and adults was dominated by members of the following genera: Lactococcus, Acinetobacter, Pantoea, Rahnella, Stenothrophomonas, Erwinia, Enterobacter, Serratia, Janibacter, Leifsonia, Cellulomonas, and Cellulosimicrobium. The members of the last four genera showed cellulolytic activity in vitro and could be involved in cellulose breakdown in the insect gut. Finally, nitrogen fixation was demonstrated in live larvae and adults; however, capacity of nitrogen fixing in vitro was not found among enterobacterial species isolated in nitrogen-free media; neither were nifD nor nifH genes detected. In contrast, nifD gen was detected in metagenomic DNA from insect guts. The identification of bacterial species and their potential physiological capacities will allow exploring the role of gut symbiotic bacteria in the adaptation and survival of D. valens in a harsh chemical habitat poor in nitrogen sources.     

IMPACT OF IMMUNE RESPONSE OF A PARASITIC BEETLE Dastarcus helophoroides ON ITS HOST BEETLE Monochamus alternatus

Dastarcus helophoroides is an ectoparasitoid beetle of Monochamus alternatus, and the parasitism by D. helophoroides larvae remarkably influenced on the immune responses of M. alternatus larvae in many aspects. The hemolymph melanization reactions in the hosts were inhibited 1 h and 24 h postparasitization. The phenoloxidase activities of hemolymph were significantly stimulated 4 h postparasitization and inhibited 12 h postparasitization, and back to control level. The antibacterial activities of hemolymph in the parasitized hosts were significantly lower than that in the unparasitized ones 1 h postparasitization. By 72 h postparasitism, the total hemocyte numbers of the parasitized larvae declined to not more than one‐seconds of the number collected from the unparasitized larvae. All sampled hemolymph held the capability of nodulation, and there were fluctuations in the number of nodules the hemocytes made. However, there were no significant differences between unparasitized and parasitized larvae at each time point in the hemagglutination activity and the ratios of spreading hemocytes. In conclusion, D. helophoroides larvae could regulate M. alternatus immune system and resulted in the changes in host immune responses.     

The effects of α‐pinene on the feeding performance and pheromone production of Dendroctonus valens

Herbivorous insects exploit multiple plant cues to detect and orient toward suitable hosts and, accordingly, hosts have evolved complex constitutive and inducible defenses in response. In China, the red turpentine beetle, Dendroctonus valens LeConte (Coleoptera: Curculionidae: Scolytinae), an invasive bark beetle from North America, attacks mainly Pinus tabuliformis Carrière (Pinaceae), which contains many monoterpenes. In this study, we explored how the monoterpene α‐pinene affects the feeding performance and pheromone production of D. valens. First, the composition and quantities of monoterpenes of both P. tabuliformis healthy trees and fresh stumps were determined and the infestation of D. valens in healthy trees and fresh stumps was investigated, linking the amount of monoterpenes and D. valens infestation. Gas chromatography–mass spectrometry (GC‐MS) analysis showed that P. tabuliformis mainly contained α‐pinene, with concentrations of 0.1 and 0.5 mg g^?1 in healthy pine phloem and stump phloem, respectively. Second, the monoterpene's influence on feeding performance was tested using phloem media with α‐pinene concentrations ranging from 0 to 30 mg g^?1. The results showed that the percentages of beetles boring and the gallery lengths of both adult females and larvae were negatively correlated with the α‐pinene concentration although body weight changes did not correlate with α‐pinene concentration. Finally, pheromone analysis showed that the production of all pheromones increased with increasing α‐pinene concentrations. This study showed the dual effects of α‐pinene on D. valens: α‐pinene inhibited the bark beetle's feeding activities and in turn the bark beetle made use of it to produce pheromones. Our study indicated the importance of promptly removing fresh stumps in the field for the management of the bark beetle.     

Biology,demography and community interactions of Tarsonemus (Acarina: Tarsonemidae) mites phoretic on Dendroctonus frontalis (Coleoptera: Scolytidae)

1 Dendroctonus frontalis, the southern pine beetle, is associated with a diverse community of fungi and mites that are phoretic on the adult beetles. Tarsonemus ips, T. kranzti and T. fusarii (Acarina: Tarsonemidae) may interact within this community in ways that link the population dynamics of D. frontalis, the mites and three dominant species of fungi. We explored species associations by comparing the dietary suitability of different fungi for Tarsonemus spp. 2 All three mite species fed and reproduced at high rates when feeding on the bluestain fungus, Ophiostoma minus, which is an antagonist of D. frontalis larvae. 3 Mites also had positive population growth rates when feeding upon Ceratocystiopsis ranaculosus, one of the mycangial fungi, but could barely reproduce when feeding upon Entomocorticium sp. A, the mycangial fungus that is most suitable for D. frontalis. 4 During the time from colonization of a tree by D. frontalis adults until departure from the tree of their progeny (≈ 40 d at 30 °C), mite populations feeding upon O. minus can increase by factors of up to 209 (T. fusarii), 173 (T. ips) or 384 (T. krantzi). These high growth rates are allowed by rapid development (age of first reproduction = 8–9 d), high fecundity (≈ 1 egg/d) and high longevity (> 28 d). 5 Precocious mating increases the chance that females are mated prior to colonizing a new tree and arrhenotokous parthenogenesis permits reproduction by unmated females. 6 Tarsonemus mites may introduce negative feedback into D. frontalis population dynamics by generating indirect interactions between D. frontalis and O. minus.     

Host resistance in defoliated pine: effects of single and mass inoculations using bark beetle-associated blue-stain fungi

1 In 1996, 7000 ha of pine forests were defoliated by the pine looper Bupalus piniaria in south‐western Sweden. 2 The susceptibility of trees of different defoliation classes (0, 30, 60, 90 and 100% defoliation) to beetle‐vectored blue‐stain fungi was tested in inoculation experiments. Forty and 120‐year‐old Scots pine trees were inoculated with ‘single’, i.e. a few inoculations of Leptographium wingfieldii and Ophiostoma minus, two blue‐stain fungi associated with the pine shoot beetle Tomicus piniperda. The young trees were also ‘mass’ inoculated with L. wingfieldii at a density of 400 inoculation points per m² over a 60 cm stem belt. 3 Host tree symptoms indicated that only trees with 90–100% defoliation were susceptible to the mass inoculation. 4 Single inoculations did not result in any consistent differences in fungal performance between trees of different defoliation classes, regardless of inoculated species or tree age class. 5 Leptographium wingfieldii produced larger reaction zones than O. minus, and both species produced larger lesions in old than in young trees. 6 As beetle‐induced tree mortality in the study area occurred only in totally defoliated stands, mass inoculations seem to mimic beetle‐attacks fairly well, and thus seem to be a useful tool for assessing host resistance. 7 As even severely defoliated pine trees were quite resistant, host defence reactions in Scots pine seem to be less dependent on carbon allocation than predicted by carbon‐based defence hypotheses.     

Invasive bark beetle‐associated microbes degrade a host defensive monoterpene

Conifers respond to herbivore attack with defensive chemicals, which are toxic to both insects and their associated microorganisms. Microorganisms associated with insects have been widely reported to metabolize toxic chemicals, which may help both microorganisms and host insects overcome host conifer defense. Dendroctonus valens LeConte, an introduced exotic pest from North America to China, has killed millions of healthy pines. Alpha‐pinene is the most abundant defensive monoterpene in Chinese Pinus tabuliformis. Although microorganisms associated with D. valens have already been investigated, little is known about their bioactivities when encountering host defensive monoterpenes. In this study, we evaluated the influences of different concentrations of α‐pinene to D. valens and the three most frequently isolated yeasts and bacteria of D. valens, and further assayed microorganisms’ capabilities to degrade α‐pinene. Results showed that the gallery lengths and body weight changes of bark beetles were significantly affected by 6 mg/mL and 12 mg/mL of α‐pinene applied in media compared to controls. The tolerance of experimental microorganisms to α‐pinene varied depending on the microbial species. Two out of three yeast strains and all three bacterial strains degraded 20%–50% of α‐pinene compared to controls in 24 h in vitro. The microorganisms capable of α‐pinene degradation in vitro and their tolerance to high levels of α‐pinene suggested that D. valens‐associated microorganisms may help both microorganisms and the bark beetle overcome host α‐pinene defense.     

Large Shift in Symbiont Assemblage in the Invasive Red Turpentine Beetle

Changes in symbiont assemblages can affect the success and impact of invasive species, and may provide knowledge regarding the invasion histories of their vectors. Bark beetle symbioses are ideal systems to study changes in symbiont assemblages resulting from invasions. The red turpentine beetle (Dendroctonus valens) is a bark beetle species that recently invaded China from its native range in North America. It is associated with ophiostomatalean fungi in both locations, although the fungi have previously been well-surveyed only in China. We surveyed the ophiostomatalean fungi associated with D. valens in eastern and western North America, and identified the fungal species using multi-gene phylogenies. From the 307 collected isolates (147 in eastern North America and 160 in western North America), we identified 20 species: 11 in eastern North America and 13 in western North America. Four species were shared between eastern North America and western North America, one species (Ophiostoma floccosum) was shared between western North America and China, and three species (Grosmannia koreana, Leptographium procerum, and Ophiostoma abietinum) were shared between eastern North America and China. Ophiostoma floccosum and O. abietinum have worldwide distributions, and were rarely isolated from D. valens. However, G. koreana and L. procerum are primarily limited to Asia and North America respectively. Leptographium procerum, which is thought to be native to North America, represented >45% of the symbionts of D. valens in eastern North America and China, suggesting D. valens may have been introduced to China from eastern North America. These results are surprising, as previous population genetics studies on D. valens based on the cytochrome oxidase I gene have suggested that the insect was introduced into China from western North America.     

Saccharide-mediated antagonistic effects of bark beetle fungal associates on larvae

Bark beetles are among the most destructive of pine forest pests and they form close symbiotic relationships with ophiostomatoid fungi. Although some fungi are considered to be mutualistic symbionts of bark beetles with respect to the supply of nutrients, detrimental effects of fungal symbionts on larval growth have also been frequently reported. The mechanisms of such antagonistic effects are hypothesized to be a decrease in nutritional resources caused by competition for saccharides by the fungi. Here, we provide experimental evidence that three beetle-associated fungi modify the nutritional content of an artificial phloem diet, leading to a detrimental effect on the growth of Dendroctonus valens larvae. When larvae were fed a diet of pine phloem in agar medium colonized with any of these fungi, feeding activity was not affected but weight significantly decreased. Additional analysis showed that fungi depleted the fructose and glucose concentrations in the phloem media. Furthermore, these detrimental effects were neutralized by supplementing the media with fructose or glucose, suggesting that fungi may affect larval growth by modifying diet saccharide contents. These data indicate that fungus-induced nutritional changes in bark beetle diet can affect larval growth, and that the mechanism involves fungus-induced saccharide depletion from the larval diet.     

Presence of weed fungus in a non‐social beetle–fungus cultivation mutualism

1. Farming by non‐human organisms has arisen independently in several animal lineages, allowing them to survive on food sources that are otherwise difficult to access. However, agricultural gardens are prone to invasion by parasites that overgrow cultivars in the absence of host animals. The presence of garden parasites and associated host adaptations are well studied in advanced fungal agriculture practised by social insects (ants, termites, and ambrosia beetles), but the impact of garden parasites in more primitive forms of agriculture is poorly known. The aim of the present study was to report the presence of weed fungi in fungal gardens of the non‐social lizard beetle Doubledaya bucculenta Lewis (Coleoptera: Erotylidae: Languriinae), which cultivates the yeast Wickerhamomyces anomalus (E.C. Hansen) Kurtzman, Robnett & Bas.‐Powers in the internodes of recently dead bamboo culms. 2. The filamentous fungi Arthrinium spp., Fusarium spp., and an unidentified species were isolated from the inner wall and insect‐made wall debris of bamboo internodes inhabited by the beetle. 3. When cultured together with the yeast in the absence of host larvae, Arthrinium sp.1 outcompeted the yeast, suggesting that this filamentous fungus can invade yeast gardens but is normally suppressed under natural conditions. 4. Rearing experiments showed that beetle larvae grew faster when grown on yeast cultures than when fed only Arthrinium sp.1. 5. These results suggest that Arthrinium sp.1 acts as a weed in the fungal gardens of D. bucculenta, inhibiting both growth of the beetle larvae and proliferation of the beneficial yeast.     

三种松树内生真菌的分离鉴定及其对红脂大小蠹伴生真菌的拮抗作用

【背景】松树的内生真菌会影响红脂大小蠹及其伴生真菌的生长及扩散,从而影响红脂大小蠹的入侵。【目的】掌握赤峰地区红脂大小蠹寄主树种内生真菌的物种多样性,筛选对其伴生菌有拮抗作用的菌株,为红脂大小蠹的生物防治提供资源。【方法】采用组织分离法、形态学鉴定和internal transcribed spacer (ITS)序列分析相结合的方法对红脂大小蠹寄主树种油松、樟子松和潜在寄主落叶松进行内生真菌多样性研究,并用两点对峙法进行拮抗菌株筛选。【结果】松树内生真菌鉴定为2门6纲10目18科19属,其中落叶松韧皮部分离到的内生真菌数量最多,为39株,隶属于9属12种,真菌检出率为43.33%;油松次之,为30株,隶属于7属8种,真菌检出率为33.33%;樟子松最少,为29株,隶属于10属13种,真菌检出率为32.22%。3个树种的内生真菌相似性较低,无共有的菌种,青霉属(Penicillium)和篮状菌属(Talaromyces)是唯二的共有菌属,且青霉属在3个树种中均为优势菌属。平板对峙结果表明90%以上的树木内生真菌均能够与伴生真菌形成稳定的对峙,抑制率在50%-86%之间,且Phialocephala sp.和Pochonia bulbillosa对伴生菌的抑制率能高达93.7%。【结论】松树韧皮部的内生真菌具有较高的生防潜力,Phialocephala sp.和P. bulbillosa对红脂大小蠹伴生菌有较好的抑制效果,可作为红脂大小蠹的生防资源。     

Nitrogen-Fixing and Uricolytic Bacteria Associated with the Gut of Dendroctonus rhizophagus and Dendroctonus valens (Curculionidae: Scolytinae)

The bark beetles of the genus Dendroctonus feed on phloem that is a nitrogen-limited source. Nitrogen fixation and nitrogen recycling may compensate or alleviate such a limitation, and beetle-associated bacteria capable of such processes were identified. Raoultella terrigena, a diazotrophic bacteria present in the gut of Dendroctonus rhizophagus and D. valens, exhibited high acetylene reduction activity in vitro with different carbon sources, and its nifH and nifD genes were sequenced. Bacteria able to recycle uric acid were Pseudomonas fluorescens DVL3A that used it as carbon and nitrogen source, Serratia proteomaculans 2A CDF and Rahnella aquatilis 6-DR that used uric acid as sole nitrogen source. Also, this is the first report about the uric acid content in whole eggs, larvae, and adults (male and female) samples of the red turpentine beetle (Dendroctonus valens). Our results suggest that the gut bacteria of these bark beetles could contribute to insect N balance.     

Red turpentine beetle primary attraction to β-pinene or 3-carene (with and without ethanol) varies in western US pine forests

1. Lure attraction strength for red turpentine beetle, Dendroctonus valens (Coleoptera: Curculionidae: Scolytinae) observed previously in US Pacific Northwest ponderosa pine forests is (−)-β-pinene+ethanol > (+)-3-carene+ethanol, but untested elsewhere in its western US range. Thus, both were tested with (−)-β-pinene, (+)-3-carene, ethanol, and a blank in Oregon and California sites burned by wildfire, whereas in Arizona the first four lures were tested in a thinned-unburned site.
2. The D. valens responses in burned Oregon and California sites were similar, (−)-β-pinene+ethanol > (−)-β-pinene > 3-carene = 3-carene+ethanol > ethanol > blank, whereas in the cut-unburned Arizona site it was 3-carene+ethanol > 3-carene = (−)-β-pinene+ethanol > (−)-β-pinene. Whether this variation was influenced by beetle genetic differences, or chemical and physical parameters in the different environments and remaining stressed host resources 1-year post disturbance warrants additional study.
3. Responses to (−)-β-pinene varied, from a stronger attractant than (+)-3-carene in Oregon and California, to a weaker lure than (+)-3-carene in Arizona. This (−)-β-pinene variability was minimized when released in combination with ethanol, making (−)-β-pinene+ethanol the most consistent attractant of those tested across the three states, and a reliable lure for detection, monitoring, and management projects for D. valens in western US pine forests.

     

The red turpentine beetle, <Emphasis Type="Italic">Dendroctonus valens</Emphasis> LeConte (Scolytidae): an exotic invasive pest of pine in China

An exotic invasive pest of pines, the red turpentine beetle, Dendroctonus valens LeConte (Scolytidae) (RTB), was first detected in Shanxi Province, northern China, in 1998 and started causing widespread tree mortality there in 1999. This outbreak continues and has spread to three adjacent provinces, causing unprecedented tree mortality. Although it is considered a minor pest of pines in North America, RTB has proven to be an aggressive and destructive pest of Pinus tabuliformis, China’s most widely planted pine species. The bionomics and occurrence, distribution, response to host volatiles, and host preference of this pine beetle in China are compared with what is known of the beetle in its native range in North America. Factors likely contributing to D. valens success in China and control of the beetle outbreak are discussed. (−)-β-pinene was shown to be the most attractive host volatile for D. valens from the Sierra Nevada of California, whereas 3-(+)-carene is the most attractive host volatile for beetles in China. Monocultures of Pinus tabuliformis, several consecutive years of drought conditions and warm winters have apparently factored D. valens invasion and establishment in China.