Four new Ophiostoma species associated with hardwood-infesting bark beetles in Norway and Poland

Ophiostoma spp. (Ophiostomatales, Ascomycota) are well-known fungi associated with bark and ambrosia beetles (Curculionidae: Scolytinae, Platypodinae). Fungi in the Ophiostomatales include serious tree pathogens as well as agents of timber blue-stain. Although these fungi have been extensively studied in the northern hemisphere, very little is known regarding their occurrence on hardwoods in Europe. The aims of the present study were to identify and characterize new Ophiostoma spp. associated with bark and ambrosia beetles infesting hardwoods in Norway and Poland, and to resolve phylogenetic relationships of Ophiostoma spp. related to the Norwegian and Polish isolates, using multigene phylogenetic analyses. Results obtained from five gene regions (ITS, LSU, β-tubulin, calmodulin, translation elongation factor 1-α) revealed four new Ophiostoma spp. These include Ophiostoma hylesinum sp. nov., O. signatum sp. nov., and O. villosum sp. nov. that phylogenetically are positioned within the Ophiostoma ulmi complex. The other new species, Ophiostoma pseudokarelicum sp. nov. reside along with Ophiostoma karelicum in a discrete, well-supported phylogenetic group in Ophiostoma s. stricto. The results of this study clearly show that the diversity and ecology of Ophiostoma spp. on hardwoods in Europe is poorly understood and that further studies are required to enrich our knowledge about these fungi.     

Cold tolerance and invasive potential of the redbay ambrosia beetle (<Emphasis Type="Italic">Xyleborus glabratus</Emphasis>) in the eastern United States

Native Lauraceae (e.g. sassafras, redbay) in the southeastern USA are being severely impacted by laurel wilt disease, which is caused by the pathogen Raffaelea lauricola T. C. Harr., Fraedrich and Aghayeva, and its symbiotic vector, the redbay ambrosia beetle (Xyleborus glabratus Eichhoff). Cold temperatures are currently the only viable limitation to the establishment of X. glabratus in northern populations of sassafras. The observed lower lethal temperature of X. glabratus (? 10.0 °C) is warmer than its supercooling point (? 22.0 °C), indicating the beetle is a freeze intolerant and chill susceptible species. Empirically derived X. glabratus lower lethal temperature thresholds were combined with host distribution and microhabitat-corrected climate data to produce species distribution models for X. glabratus in the eastern USA. Macroclimate data (30-year mean annual minimum temperature) were corrected (? 1.2 °C) to account for thermal buffering afforded to X. glabratus while living inside sassafras trees. Only 0.1% of the current US sassafras spatial extent experiences sufficiently harsh winters (locales where mean annual minimum winter temperatures ≤ ? 6.2 °C for ≥ 12 h) to exclude X. glabratus establishment in our species distribution model. Minimum winter temperatures will likely cause some X. glabratus mortality in ~ 52% of the current spatial extent of sassafras, although current data do not allow a quantification of X. glabratus mortality in this zone. Conversely, ~ 48% of the current spatial extent of sassafras is unlikely to experience sufficiently cold winter temperatures to cause any significant impediment to X. glabratus spread or establishment. A modest climate change scenario (RCP4.5) of + 1.4 °C would result in 91% of the current spatial extent of sassafras in the eastern USA occurring where winter minimum temperatures are unlikely to cause any mortality to X. glabratus.     

Ancient and modern colonization of North America by hemlock woolly adelgid,Adelges tsugae (Hemiptera: Adelgidae), an invasive insect from East Asia

Hemlock woolly adelgid, Adelges tsugae, is an invasive pest of hemlock trees (Tsuga) in eastern North America. We used 14 microsatellites and mitochondrial COI sequences to assess its worldwide genetic structure and reconstruct its colonization history. The resulting information about its life cycle, biogeography and host specialization could help predict invasion by insect herbivores. We identified eight endemic lineages of hemlock adelgids in central China, western China, Ulleung Island (South Korea), western North America, and two each in Taiwan and Japan, with the Japanese lineages specializing on different Tsuga species. Adelgid life cycles varied at local and continental scales with different sexual, obligately asexual and facultatively asexual lineages. Adelgids in western North America exhibited very high microsatellite heterozygosity, which suggests ancient asexuality. The earliest lineages diverged in Asia during Pleistocene glacial periods, as estimated using approximate Bayesian computation. Colonization of western North America was estimated to have occurred prior to the last glacial period by adelgids directly ancestral to those in southern Japan, perhaps carried by birds. The modern invasion from southern Japan to eastern North America caused an extreme genetic bottleneck with just two closely related clones detected throughout the introduced range. Both colonization events to North America involved host shifts to unrelated hemlock species. These results suggest that genetic diversity, host specialization and host phylogeny are not predictive of adelgid invasion. Monitoring non‐native sentinel host trees and focusing on invasion pathways might be more effective methods of preventing invasion than making predictions using species traits or evolutionary history.     

Tree species and position matter: the role of pests for survival of other insects

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Dispersal of the nuclear polyhedrosis virus of Neodiprion sertifer from soil to pine foliage with dust

Inclusion bodies (PIB) of nuclear polyhedrosis viruses (NPV) remain infectious for long periods in forest soils, but their transfer from soil to foliage is not well understood. Two instances of dispersal of the NPV of Neodiprion sertifer (Fourcroy) (Hymenoptera: Diprionidae) by dust are reported. The distributioo of diseased larval colonies in a young Scots pine stand indicated that dust caused by logging during winter could have started an epizootic. At another site there was a higher frequency of infected colonies near a forest road than further into the stand. The dust transmission hypothesis was tested by bioassays of road surface material and of samples of airborne dust collected on membrane filters. Both soil and air samples contained viable PIBs. Thus, virus dispersal with dust provided a likely explanation for the observed distributions of diseased larval colonies.

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Zusammenfassung Mortalität von N.sertifer Larven durch das wirtsspezifische Kernpolyedervirus ist zwischen den Massenvermehrungen der Sägewespe selten. Eine ständige Infektionskette bleibt nicht erhalten. Das einzige bekannte Reservoir von Virusinoculum zwischen den Massenvermehrungen ist der Waldboden. Die Übertragung von Virus vom Boden auf Kiefernnadeln wird als seltenes Ereignis betrachtet. Sie dürfte häufiger sein, wenn die bodenbedeckende Vegetation gestört ist. Es wird von zwei Studien berichtet, in denen offenbar NPV in windverfrachtetem Staub die Krankheit bei Larven verursachte.In einem jungen Bestand schottischer Kiefer, in dem keine neueren Meldungen von Virusauftreten vorlagen, wurden Proben genommen. Die Proben stammten aus verschiedenen Distanzen von einem ausgewachsenen, im vorherigen Winter gefällten Bestand. Die Befallsintensität sank hier scharf ab mit zunehmender Distanz vom Rand.Ferner wurde der Krankheitsbefall in Larvenkolonien an kleinen Bäumen nahe einer schmalen Forst-strasse und an Bäumen im Bestandesinnern untersucht: In Strassennähe war der Befall höher. Luftmuster wurden nahe der Strasse durch Membranfiltern gesaugt und in einem Biotest auf Virus untersucht. Wenn die Strassenoberfläche ungestört war, wurde kein Virus festgestellt. Wurde Staub aufgewirbelt, konnten infektiöse PIBs gefunden werden. Material von der Strassenoberfläche hatte eine hohe Virusaktivität.Die Übertragung des Virus vom Boden auf Kiefernnadeln dürfte demnach wichtig sein, um Krankheitsausbrüche auszulösen. Die beschriebenen Störungen waren vom Menschen verursacht. Ähnliches könnte sich unter andern Umständen ereignen, z.B. bei Windfall oder bei der Aktivität grösserer Tiere.

     

Modelling the effects of climate change on the potential feeding activity of Thaumetopoea pityocampa (Den. & Schiff.) (Lep., Notodontidae) in France

Aim We investigated whether climate change has affected the potential feeding activity of a winter active larva, the pine processionary moth (PPM), Thaumetopoea pityocampa L., and whether it may explain its range expansion. Location The study area is France and, at a smaller scale, the Paris Basin. Methods We used a statistical model derived from Huchon and Démolin [1970 Revue Forestière Française (special issue: La lutte biologique en forêt), 220–234] to test whether their model, updated with climate change, could explain the observed range expansion. Since Battisti and colleagues have recently shown that climate could affect survival of the PPM through its effect on feeding activity, we also developed a mechanistic model based on larval feeding requirements (night air temperature above 0 °C and temperature inside the nest above 9 °C on the preceding day). We reconstructed the geographical distribution of feeding activity and we compared the resulting change with the PPM range expansion. Results The statistical model did not successfully predict the observed expansion but the mechanistic model showed considerable change in the feeding activity of the PPM. In the Paris Basin, the PPM border coincided with a zone unfavourable for feeding activity in the period 1992–96. Feeding conditions became more favourable in the period 2001–04, and the PPM succeeded in crossing this zone. Over larger temporal and spatial scales improved feeding conditions in the north‐western part of France were forecast by the mechanistic model. Main conclusions (1) The range distribution of the PPM in the Paris Basin is no longer limited by unfavourable feeding conditions. (2) The pattern of range expansion of the PPM is now governed mainly by its dispersal capabilities and host tree distribution. (3) At the country scale, this approach gives an approximate prediction of the potential distribution of the PPM, though the model may not be reliable in mountainous regions.     

Fungal community composition in the gut of rove beetles (Coleoptera: Staphylinidae) from the Canadian boreal forest reveals possible endosymbiotic interactions for dietary needs

The goal of this study was to investigate the fungal community composition in the gut of Staphylinidae from boreal forest in order to better understand the diversity and the complexity of fungus-insect relationships. DNA gut content analyses of nine abundant rove beetle species (Coleoptera, Staphylinidae) living in the boreal balsam fir forest ecosystem (Montmorency Forest, Quebec, Canada) were performed to identify the fungal taxa present either as endosymbiotic taxa or as a source of nutrition. A total of 42 fungal operational taxonomic units (OTUs) were recorded from the analysis of 441 fungal ITS rDNA sequences recovered from gut extracts. The OTU richness per species ranged between four in Tachinus quebecensis and 16 in Atheta ventricosa. The fungal mycobiota in posterior gut extracts was dominated by Saccharomycetales (12 OTUs), followed by Sordariomycetes (nine OTUs). No significant difference was observed between the OTU richness recorded within each of the three subfamilies of rove beetles investigated. The core mycobiome of the posterior gut extracts was dominated by three OTUs related to yeasts, with ITS sequences having pairwise similarities equal to or greater than 99% with Candida mesenterica, Debaryomyces spp. and Ophiostoma pluriannulatum. These results provide some evidence of the consumer-resource relationships of these beetles. Predominance of yeast and fungal spores in the posterior gut of rove beetles suggests that they may play an important role in their dietary requirements and as endosymbionts.     

Pheromone production in bark beetles

The first aggregation pheromone components from bark beetles were identified in 1966 as a mixture of ipsdienol, ipsenol and verbenol. Since then, a number of additional components have been identified as both aggregation and anti-aggregation pheromones, with many of them being monoterpenoids or derived from monoterpenoids. The structural similarity between the major pheromone components of bark beetles and the monoterpenes found in the host trees, along with the association of monoterpenoid production with plant tissue, led to the paradigm that most if not all bark beetle pheromone components were derived from host tree precursors, often with a simple hydroxylation producing the pheromone. In the 1990s there was a paradigm shift as evidence for de novo biosynthesis of pheromone components began to accumulate, and it is now recognized that most bark beetle monoterpenoid aggregation pheromone components are biosynthesized de novo. The bark beetle aggregation pheromones are released from the frass, which is consistent with the isoprenoid aggregation pheromones, including ipsdienol, ipsenol and frontalin, being produced in midgut tissue. It appears that exo-brevocomin is produced de novo in fat body tissue, and that verbenol, verbenone and verbenene are produced from dietary α-pinene in fat body tissue. Combined biochemical, molecular and functional genomics studies in Ips pini yielded the discovery and characterization of the enzymes that convert mevalonate pathway intermediates to pheromone components, including a novel bifunctional geranyl diphosphate synthase/myrcene synthase, a cytochrome P450 that hydroxylates myrcene to ipsdienol, and an oxidoreductase that interconverts ipsdienol and ipsdienone to achieve the appropriate stereochemistry of ipsdienol for pheromonal activity. Furthermore, the regulation of these genes and their corresponding enzymes proved complex and diverse in different species. Mevalonate pathway genes in pheromone producing male I. pini have much higher basal levels than in females, and feeding induces their expression. In I. duplicatus and I. pini, juvenile hormone III (JH III) induces pheromone production in the absence of feeding, whereas in I. paraconfusus and I. confusus, topically applied JH III does not induce pheromone production. In all four species, feeding induces pheromone production. While many of the details of pheromone production, including the site of synthesis, pathways and knowledge of the enzymes involved are known for Ips, less is known about pheromone production in Dendroctonus. Functional genomics studies are under way in D. ponderosae, which should rapidly increase our understanding of pheromone production in this genus. This chapter presents a historical development of what is known about pheromone production in bark beetles, emphasizes the genomic and post-genomic work in I. pini and points out areas where research is needed to obtain a more complete understanding of pheromone production.     

Impact of a juvenile hormone analogue on the anatomy and the frontal gland secretion of Prorhinotermes simplex (Isoptera: Rhinotermitidae)

In termites, juvenile hormone plays a key role in soldier differentiation. To better understand the evolutionary origin of the soldiers, we studied the external and inner morphology of pseudergate-soldier intercastes and neotenic-soldier intercastes formed artificially by the application of juvenile hormone analogue in Prorhinotermes simplex. A majority of these intercastes had a soldier phenotype, whereas the inner anatomy had an intermediary form between two castes or a form specific to intercastes. Our experiments showed that traits of neotenics and soldiers can be shared by the same individuals, although such individuals do not exist naturally in P. simplex, and they have not been reported in other species but in some Termopsidae. Our results reinforce the hypothesis that soldiers may have emerged from soldier neotenics during the evolution of termites.