Dominant bacteria associated with broods of mountain pine beetle, Dendroctonus ponderosae (Coleoptera: Curculionidae, Scolytinae)

Mountain pine beetle (MPB) is the most damaging insect of mature pine forests in western North America. The current outbreak in British Columbia is the largest ever recorded. During a survey of beetle occurrence, well—established infestations were sampled in central B.C. and found to possess larval mortality. Bacteria or other microbes were among the potential causes of the mortality. Bacteria were isolated from living larvae and adults, as well as larval and adult beetle cadavers found in bark samples. Bacteria were identified by fatty acid methyl ester (FAME) analysis, which indicated 32 species of bacteria present in the MPB laivae. The predominant bacteria (Serratia liquefaciens, S. plymuthica) were detected in about a third of all sampled laivae, regardless of mortality. Rahnella aquatilis was found in 11% of all larvae examined and was usually (93%) associated with laival mortality. Interactions between two bluestaining fungal symbionts of the MPB (Grosmannia clavigera, Ophiostoma montium) and two of the isolated bacteria (S. liquefaciens and R. aquatilis) were assessed. S. liquefaciens and R. aquatilis both inhibited the growth of beetle-associated bluestain fungi by 72%. The bluestain fungi did not impede bacterial growth, and both bacteria grew on autoclaved bluestain mycelium. Combinations of the two bacterial species formed aggregates on practical-grade (crab) chitin, but there was no aggregation in pure cultures or on the autoclaved mycelium of G. clavigera or O. montium. These results indicated that the two bacteria may be capable of aggregation within the insects, and this may have implications for their combined effects in the beetle. The role of S. liquefaciens and R. aquatilis in MPB biology requires further investigation