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

The eastern larch beetle (Dendroctonus simplex Le 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 larch stands. Dendroctonus species are considered as holobionts, as they engage in multipartite interactions 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 beetle's attack, as they are responsible for the detoxification of the subcortical environment and weaken the tree's defense mechanisms. The eastern larch beetle 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 beetle's requirements. These results indicate that a symbiotic association between the eastern larch beetle 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.

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

The eastern larch beetle (Dendroctonus simplex Le 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 larch stands. Dendroctonus species are considered as holobionts, as they engage in multipartite interactions 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 beetle’s attack, as they are responsible for the detoxification of the subcortical environment and weaken the tree’s defense mechanisms. The eastern larch beetle 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 beetle’s requirements. These results indicate that a symbiotic association between the eastern larch beetle 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.

Fungal communities associated with the eastern larch beetle: diversity and variation within developmental stages

Bacterial and fungal communities associated with bark beetles, especially some Dendroctonus species, mediate challenging aspects of the subcortical habitat for their hosts. Filamentous fungi and yeasts are important in various metabolic processes of certain bark beetles, with involvement in nutrition, protection and detoxification of plant defense compounds. The eastern larch beetle, Dendroctonus simplex, is recognized as a serious forest pest in the upper part of North America. Although D. simplex is well studied, the fungal communities and their ecological role remain to be investigated. Here, using 18S rRNA gene pyrosequencing, we provide a comprehensive overview of the yeasts and filamentous fungi associated with the eastern larch beetle and compare fungal communities between different developmental stages and microenvironments. Fungal mycobiome associated with the galleries was also investigated. Our study has unveiled an unexpected fungal diversity associated with the developmental stages. Significant differences in species richness between the developmental stages were determined. Yeasts were found to be predominant in the adult and larval stages, whereas filamentous fungi were most prevalent in the pupae. Our results indicate a possible implication of yeasts in the eastern larch beetle nutrition.

A new species of Ophiostoma from North America, similar to Ophiostoma penicillatum

Ophiostomatoid fungi that resemble Ophiostoma penicillatum were isolated from insect-infested spruce (Picea sp.) in Japan as well as Larix decidua Mill. (European larch) in North America. Isolates were characterized based on morphology and could be separated into two distinct groups. Those from spruce in Japan represent O. penicillatum, and are characterized by allantoid, slightly curved conidia. The North American isolates from Larix decidua are of a previously undescribed species, characterized by long, narrow conidia. The latter fungus is described as Ophiostoma americanum with an anamorph, Leptographium americanum. Key words: Ophiostoma penicillatum, Ips typographus, Ophiostoma americanum, Dendroctonus simplex, Larix decidua.

The Eastern Larch Beetle, Another Threat to our Forests (Coleoptera: Scolytidae)

Isolated infestations of the eastern larch beetle, Dendroctonus simplex LeConte, have been reported in North America for over 100 years. Historically, this species has been considered a secondary pest of tamarack, Larix laricina (Du Roi) K. Koch, infesting only weakened or recently felled host material. However, recent widespread outbreaks of this bark beetle in northeastern North America and Alaska suggest that the species can be a primary killer of trees. More than 1.4 million m3 of tamarack was killed in the Atlantic provinces of Canada from 1976 to 1986. No damage estimates are available for Quebec and the United States. Fire, flooding, drought and defoliation by insects are often important agents predisposing tamarack to beetle attack and fostering localized build-up of D. simplex populations which then spread to healthy stands resulting in a widespread outbreak. Key Words: Dendroctonus simplex, bark beetle, outbreaks, damage appraisal, predisposing agents, tamarack.