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.     

Large carbon release legacy from bark beetle outbreaks across Western United States

Warmer conditions over the past two decades have contributed to rapid expansion of bark beetle outbreaks killing millions of trees over a large fraction of western United States (US) forests. These outbreaks reduce plant productivity by killing trees and transfer carbon from live to dead pools where carbon is slowly emitted to the atmosphere via heterotrophic respiration which subsequently feeds back to climate change. Recent studies have begun to examine the local impacts of bark beetle outbreaks in individual stands, but the full regional carbon consequences remain undocumented for the western US. In this study, we quantify the regional carbon impacts of the bark beetle outbreaks taking place in western US forests. The work relies on a combination of postdisturbance forest regrowth trajectories derived from forest inventory data and a process‐based carbon cycle model tracking decomposition, as well as aerial detection survey (ADS) data documenting the regional extent and severity of recent outbreaks. We find that biomass killed by bark beetle attacks across beetle‐affected areas in western US forests from 2000 to 2009 ranges from 5 to 15 Tg C yr^?1 and caused a reduction of net ecosystem productivity (NEP) of about 6.1–9.3 Tg C y^?1 by 2009. Uncertainties result largely from a lack of detailed surveys of the extent and severity of outbreaks, calling out a need for improved characterization across western US forests. The carbon flux legacy of 2000–2009 outbreaks will continue decades into the future (e.g., 2040–2060) as committed emissions from heterotrophic respiration of beetle‐killed biomass are balanced by forest regrowth and accumulation.     

一种红脂大小蠹天敌切头郭公虫Clerus sp.生物学初探

红脂大小蠹Dendroctonus valens LeConte,原产于北美,于20世纪80年代随木材贸易传入我国山西,是一种危害油松、白皮松、华山松等松科植物的毁灭性入侵害虫。本文对红脂大小蠹天敌切头郭公甲虫Clerus sp.的基本生物学特征进行了初步探讨。野外诱捕发现,红脂大小蠹诱剂3-蒈烯能诱捕到切头郭公甲虫Clerus sp.,并观察到此郭公甲虫紧抱红脂大小蠹的捕食行为及红脂大小蠹头部被切下的残骸。诱捕动态监测表明切头郭公甲虫与红脂大小蠹的发生在时间和数量上具有跟随关系。室内测定结果显示切头郭公甲虫平均体重约15.5 mg且个体大小与捕食能力呈正相关。切头郭公虫平均存活时间约38 d,10 d内平均每头郭公虫捕食3头红脂大小蠹,最多达8头。行为嗅觉试验表明切头郭公虫Clerus sp.对红脂大小蠹诱芯反应敏感,红脂大小蠹信息素组分frontalin不能增加其对红脂大小蠹诱芯的敏感性。本研究初步探明了红脂大小蠹天敌切头郭公虫Clerus sp.生物学特征,其较长捕食周期和较强的捕食能力决定其可作为红脂大小蠹的生物防治因子具有一定的优势和较好的天敌应用前景。     

Effects of bark beetle pheromones on the attraction of Monochamus alternatus to pine volatiles

Abstract We evaluated the attraction of Monochamus alternatus Hope (Coleoptera: Cerambycidae), Dryocoetes luteus Blandford and Orthotomicus erosus Wollaston (Coleoptera: Curculionidae: Scolytinae) to multiple-funnel traps baited with the pine volatiles, ethanol and (+)-α-pinene and the bark beetle pheromones, ipsenol and ipsdienol. M. alternatus were attracted to traps baited with ethanol and (+)-α-pinene but not those baited with ipsdienol and ipsenol. Ipsdienol and ipsenol decreased catches of M. alternatus in traps baited with ethanol and (+)-α-pinene. Traps baited with either binary combinations of ethanol and (+)-α-pinene or ipsdienol and ipsenol were attractive to D. luteus and O. erosus. The addition of ipsenol and ipsdienol to traps baited with ethanol and (+)-α-pinene synergized attraction of O. erosus but not D. luteus.     

Ultrastructure of the mycangium of the southern pine beetle,Dendroctonus frontalis (Coleoptera: Curculionidae,Scolytinae): complex morphology for complex interactions

Yuceer, C, Hsu, C.‐Y., Erbilgin, N and Klepzig, K.D. 2011. Ultrastructure of the mycangium of the southern pine beetle, Dendroctonus frontalis (Coleoptera: Curculionidae, Scolytinae): complex morphology for complex interactions. —Acta Zoologica (Stockholm) 92 : 216–224. The southern pine beetle (SPB) (Dendroctonus frontalis Zimmermann) is the most economically important pest of southern pine forests. Beetles carry fungal cells within specialised cuticular structures, called mycangia. Little is known about the mycangia ultrastructure or function. We used cryo‐fracturing and scanning electron microscopy to examine the ultrastructural features of SPB mycangia and surrounding tissues. Mycangia, one on each side of anterior portion of the prothorax, are terminated on the dorsal side at a ‘mycangial bridge’. This sclerotised mycangial bridge does not appear to provide a passage between the two mycangia, suggesting that each mycangium functions independently. Mycangia are surrounded by abundant tracheoles connecting the structures to the outside via openings within the prothorax. Previously unknown pits overlying the mycangial gland cells were also observed in both the inner wall and anterior fold of prothorax. We hypothesise that these openings and pits may play roles in determining which fungi enter, and grow within, the mycangium.     

小蠹虫信息素的研究与应用现状

小蠹虫是世界性林木害虫,猖獗时常可造成林木成片枯死。利用小蠹虫信息素防治该虫,不仅可以有效降低虫口密度,减轻危害程度,还可以监测小蠹虫的发生为害情况。本文从小蠹虫信息素的分离鉴定、信息素的生物合成、小蠹虫对信息素的行为反应等方面综述小蠹虫信息素的研究与应用现状。     

Experimental evidence of bark beetle adaptation to a fungal symbiont

The importance of symbiotic microbes to insects cannot be overstated; however, we have a poor understanding of the evolutionary processes that shape most insect–microbe interactions. Many bark beetle (Coleoptera: Curculionidae, Scolytinae) species are involved in what have been described as obligate mutualisms with symbiotic fungi. Beetles benefit through supplementing their nutrient‐poor diet with fungi and the fungi benefit through gaining transportation to resources. However, only a few beetle–fungal symbioses have been experimentally manipulated to test whether the relationship is obligate. Furthermore, none have tested for adaptation of beetles to their specific symbionts, one of the requirements for coevolution. We experimentally manipulated the western pine beetle–fungus symbiosis to determine whether the beetle is obligately dependent upon fungi and to test for fine‐scale adaptation of the beetle to one of its symbiotic fungi, Entomocorticium sp. B. We reared beetles from a single population with either a natal isolate of E. sp. B (isolated from the same population from which the beetles originated), a non‐natal isolate (a genetically divergent isolate from a geographically distant beetle population), or with no fungi. We found that fungi were crucial for the successful development of western pine beetles. We also found no significant difference in the effects of the natal and non‐natal isolate on beetle fitness parameters. However, brood adult beetles failed to incorporate the non‐natal fungus into their fungal transport structure (mycangium) indicating adaption by the beetle to particular genotypes of symbiotic fungi. Our results suggest that beetle–fungus mutualisms and symbiont fidelity may be maintained via an undescribed recognition mechanism of the beetles for particular symbionts that may promote particular associations through time.     

The internal microbial flora of the elm bark beetle, Scolytus scolytus, at all stages of its development

Adult Scolytus scolytus emerged from the pupal stage with sterile guts although microorganisms were present within the pupal body. Gut sterility was maintained in a large proportion of newly formed adults while they were boring out of an elm log. The adult gut microbial flora is mainly acquired during subsequent feeding. Differences were found between the microbial gut flora of both larvae and adult S. scolytus, and of both male and female beetles.     

Comparative efficacy of different pesticides against mango bark beetle Hypocryphalus mangiferae Stebbing (Coleoptera: Scolytidae)

Hypocryphalus mangiferae Stebbing is one of the most destructive insect pests of mango trees and is found to be associated with the transmission of causal organisms of mango sudden death disease. The present study was carried out to evaluate the toxicity of deltamethrin, bifenthrin, chlorpyrifos, emamectin benzoate, imidacloprid and spinosad in laboratory and field trials. Bioassay results showed that the toxicity of chlorpyrifos was significantly higher than deltamethrin but similar to bifenthrin. Deltamethrin and bifenthrin toxicity, however, increased significantly (P < 0.01) from day 1 to day 3. Spinosad was the least toxic compound while emamectin was the most toxic among new chemical insecticides tested, but its toxicity increased significantly from day 1 to day 5. Comparison of the efficacies of the insecticides using lethal times to produce 50% mortality (LT₅₀) and 90% mortality (LT₉₀) showed that the relative potencies of chlorpyrifos, emamectin, imidacloprid and spinosad were greater than bifenthrin and deltamethrin. The results of field trials showed the highest number of beetles emerged from the control twigs while significantly fewer beetles emerged from the twigs treated with bifenthrin (P < 0.05), which accounted for 12% for bifenthrin compared to that of the control. The present study demonstrated increased toxicities of systemic insecticides and chlorpyrifos compared to toxicities of deltamethrin and bifenthrin, suggesting these insecticides could be an alternative tool in a comprehensive H. mangiferae management program to eradicate the beetles from mango orchards.     

Mitochondrial DNA haplotypes indicate two postglacial re‐colonization routes of the spruce bark beetle Ips typographus through northern Europe to Scandinavia

Species in northern Europe re‐colonized the region after the last glacial maximum via several routes, which could have lingering signatures in current intraspecific trait variation. The spruce bark beetle, Ips typographus, occurs across Europe, and biological differences have been found between southern and northern Scandinavian populations. However, the postglacial history of I. typographus in Scandinavia has not been previously studied at a fine geographical scale. Therefore, we collected specimens across northern Europe and analysed the genetic variation in a quite large mitochondrial fragment (698 bp). A high genetic diversity was found in some of the most northern populations, in the Baltic States, Gotland and central Europe. Detected genetic and phylogeographic structures suggest that I. typographus re‐colonized Scandinavia via two pathways, one from the northeast and one from the south. These findings are consistent with the re‐colonization history of its host plant, Picea abies. However, we observed low haplotype and nucleotide diversity in southern Scandinavian populations of I. typographus, indicating that (unlike P. abies) it did not disperse across the Baltic Sea in multiple events. Further, the divergence among Scandinavian populations was shallow, conflicting with a scenario where I. typographus expanded concurrently with its host plant from a ‘cryptic refugium’ in the northwest.     

Differences in photoperiod‐induced diapause plasticity among different populations of the bark beetle Ips typographus and its predator Thanasimus formicarius

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Optimization of bioassay conditions for the olive bark beetle Phloeotribus scarabaeoides

Bioassay conditions with a glass olfactometer for the olive bark beetle, Phloeotribus scarabaeoides Bern. (Coleoptera: Scolytidae), have been investigated. The best temperatures and light intensities were between 17 and 28° C and 1000 and 1500 lux, respectively. The best response was obtained with newly emerged individuals from reproduction galleries with no feeding period.     

Isolation and characterization of microsatellite loci from two inbreeding bark beetle species (Coccotrypes)

We developed 14 microsatellite markers in Coccotrypes carpophagus and 14 in C. dactyliperda. These loci will be used for studying genetic structure and the level of inbreeding in populations in the Canary Islands and Madeira. As a result of long‐term inbreeding, genetic variability is relatively low in these bark beetle species. We found one to five alleles per locus in 29 C. carpophagus and 41 C. dactyliperda from various localities. Eleven of the markers developed for C. carpophagus amplified in C. dactyliperda and seven of the markers developed for C. dactyliperda amplified in C. carpophagus.     

Physiological and biochemical analysis of overwintering and cold tolerance in two Central European populations of the spruce bark beetle, Ips typographus

Overwintering success is one of the key aspects affecting the development and outbreaks of the spruce bark beetle, Ips typographus (L.) populations. This paper brings detailed analysis of cold tolerance, and its influence on overwintering success, in two Central European populations of I. typographus during two cold seasons. Evidence for a supercooling strategy in overwintering adults is provided. The lower lethal temperature corresponds well to the supercooling point that ranges between −20 and −22 °C during winter months. The supercooled state is stabilized by the absence of internal ice nucleators and by seasonal accumulation of a mixture of sugars and polyols up to the sum concentration of 900 mM. The cryoprotective function of accumulated metabolites is probably based on increasing the osmolality and viscosity of supercooled body fluids and decreasing the relative proportion of water molecules available for lethal formation of ice nuclei. No activity of thermal hysteresis factors (stabilizers of supercooled state) was detected in hemolymph. Lethal times for 50% mortality (Lts50) in the supercooled state at −5, −10 or −15 °C are weeks (autumn, spring) or even months (winter), suggesting relatively little mortality caused by chill injury. Lts50 at −15 °C are significantly shorter in moist (6.9 days) than in dry (>42 days) microenvironment because there is higher probability of external ice nucleation and occurrence of lethal freezing in the moist situation.     

Weak population genetic structure in Eurasian spruce bark beetle over large regional scales in Sweden

The Eurasian spruce bark beetle, Ips typographus, is a major pest, capable of killing spruce forests during large population outbreaks. Recorded dispersal distances of individual beetles are typically within hundreds of meters or a few kilometers. However, the connectivity between populations at larger distances and longer time spans and how this is affected by the habitat is less studied, despite its importance for understanding at which distances local outbreaks may spread. Previous population genetic studies in I. typographus typically used low resolution markers. Here, we use genome‐wide data to assess population structure and connectivity of I. typographus in Sweden. We used 152 individuals from 19 population samples, distributed over 830 km from Strömsund (63° 46′ 8″ N) in the north to Nyteboda (56° 8′ 50″ N) in the south, to capture processes at a large regional scale, and a transect sampling design adjacent to a recent outbreak to capture processes at a smaller scale (76 km). Using restriction site‐associated DNA sequencing (RADseq) markers capturing 1409–1997 SNPs throughout the genome, we document a weak genetic structure over the large scale, potentially indicative of high connectivity with extensive gene flow. No differentiation was detected at the smaller scale. We find indications of isolation‐by‐distance both for relative (F _ST) and absolute divergence (Dxy). The two northernmost populations are most differentiated from the remaining populations, and diverge in parallel to the southern populations for a set of outlier loci. In conclusion, the population structure of I. typographus in Sweden is weak, suggesting a high capacity to disperse and establish outbreak populations in new territories.     

Ecphylus silesiacus (Ratz.) (Hymenoptera, Braconidae), an important elm bark beetle parasitoid

1 Ecphylus silesiacus (Ratz.) (Hym. Braconidae) parasitizes larvae of elm bark beetles (Coleoptera: Scolytidae) occurring in thin bark. Pteleobius kraatzi (Eichh.), Scolytus pygmaeus (Fab.), Scolytus multistriatus (Marsh) and Scolytus ensifer (Eichh.) are the most suitable hosts. Scolytus scolytus (Fab.) occurring in thicker bark, is not such a suitable host for E. silesiacus. Ecphylus silesiacus only parasitized this species in bark forks. 2 Under experimental conditions, P. kraatzi produced the largest number of elm bark beetle adults per maternal gallery and had the longest development period, while S. scolytus produced the smallest number of adults and had the shortest development period. 3 Ecphylus silesiacus had the lowest reproduction, the shortest development period and the least favourable sexual ratio, on S. scolytus larvae, and the highest production, the longest developmental period and the most favourable sexual ratio on P. kraatzi and S. pygmaeus larvae. 4 Ecphylus silesiacus adults fed with Parker's diet and the nectar of the melliferous plant Daucus carota L. (Umbelliferae), lived longer, parasitized a greater percentage of S. pygmaeus larvae, and had a significant offspring production compared with adults without additional diet.     

Temperature effects on growth of fungal symbionts of the western pine beetle,Dendroctonus brevicomis

Differences in temperature ranges and optima among poikilothermic partners in symbioses can have profound effects on their interactions and stability. In this study, we investigated how the two mutualist mycangial fungi (Ceratocystiopsis brevicomi and Entomocorticium sp. B) associated with the western pine beetle, Dendroctonus brevicomis, respond to temperature in vitro. Little variability in growth rate at the various temperatures tested occurred among isolates of C. brevicomi either within or among sites. In contrast, E. sp. B exhibited highly variable responses to mid-range temperatures among sites and within some sites, and, unlike C. brevicomi, grew not at all or only very poorly at the highest and lowest temperatures tested. This variability affected both optimal temperature and maximum growth rate. The high variability in response to some temperatures among isolates of E. sp. B in some populations indicates that the ability to capture spatial and nutritional resources can vary greatly within this species which may have considerable impact on the outcome of both inter- and intra-specific competition among the fungi within trees and the short- and long-term dynamics of the fungi with the host beetle.     

Antifeedant and toxic effects of drimanes on Colorado potato beetle larvae

Among the drimane compounds tested, the dialdehydes polygodial and warburganal were the most active as antifeedants against Colorado potato beetle larvae, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), in a dual-choice assay with potato, Solanum tuberosum L., leaf discs. Lactones were less effective. Direct observations showed that decreased feeding on leaf discs treated with polygodial and warburganal was accompanied by increased locomotry activity. Topical application of these two compounds on the insect's cuticle decreased food intake of untreated leaf discs, indicating that besides deterrent effects, toxic properties of these molecules influence feeding behaviour.     

Relationship between a host plant compound,myrcene and pheromone production in the bark beetle, IPS paraconfusus

The pheromonal components, ipsenol and ipsdienol were found in increasing quantities in hindguts of only the male sex of Ips paraconfusus following exposure of both sexes to a series of increasing concentrations of myrcene vapour. Hindguts of female and male beetles contained similar quantities of myrcene and other volatile compounds associated with myrcene exposure. Unexposed beetles of both sexes did not contain detectable amounts of any volatile compound. This indicates that myrcene induces or is a precursor for sex-specific pheromone biosynthesis.     

小蠹虫对针叶类寄主树木的选择危害机制

小蠹虫对寄主植物的选择是一个非常复杂的过程,也是近年来小蠹虫生态学研究的一个热门话题。文章对国内外小蠹虫寄主搜寻、寄主识别,以及适宜寄主选择等机制等方面的最新研究成果进行了系统报道。