The symbiotic complex of Dendroctonus simplex: implications in the beetle attack and its life cycle

The eastern larchbeetle ( Dendroctonus simplexLe Conte) is recognized as a serious destructive forest pest in the upper part of North America. Under epidemic conditions, this beetle can attack healthy trees, causing severe damages to larchstands. Dendroctonusspecies are considered as holobionts, as they engage in multipartiteinteractions with microorganisms, such as bacteria, filamentous fungi, and yeasts, which are implicated in physiological processes of the insect, such as nutrition. They also play a key role in the beetle9s attack, as they are responsible for the detoxification of the subcortical environment and weaken the tree9s defense mechanisms. The eastern larchbeetle is associated with bacteria and fungi, but their implication in the success of the beetle remains unknown. Here, we investigated the bacterial and fungal microbiota of this beetle pest throughout its ontogeny (pioneer adults, larvae and pupae) by high-throughput sequencing. A successional microbial assemblage was identified throughout the beetle developmental stages, reflecting the beetle9s requirements. These results indicate that a symbiotic association between the eastern larchbeetle and some of these microorganisms takes place and that this D. simplex symbiotic complex is helping the insect to colonize its host tree and survive the conditions encountered.