Gut microbiota in an invasive bark beetle infected by a pathogenic fungus accelerates beetle mortality

Dendroctonus valens , introduced to China from North America, has caused catastrophic mortality of healthy pines and has the potential to disperse into new geographic ranges. The entomopathogen Beauveria bassiana is an environmentally friendly alternative to chemical pesticides, and it is highly lethal to D. valens . Recent studies reported that gut microbiota of insects can suppress or promote infections by B. bassiana . Although D. valens harbors an abundant gut microbiota, whether and how gut microbiota interplay with fungal entomopathogens has not been examined. Nonaxenic D. valens larvae inoculated with B. bassiana conidia died significantly faster than axenic larvae. Significant differences were found between the structures of gut bacterial communities in B. bassiana conidial suspension-inoculated and Tween 80 treated larvae, and the abundance of Erwinia sp. in the former group was significantly higher than the latter one. Reintroduction of Erwinia sp. into axenic D. valens larvae accelerated larval mortality. These observations indicate that the gut bacterial community of an invasive bark beetle is altered by entomopathogenic B. bassiana , which further accelerates beetle mortality.