Gut bacteria of woodboring Streltzoviella insularis and their involvement in pinoresinol degradation of ash tree (Fraxinus spp.) host

Abstract Insect gut microbiota have been widely reported to metabolize defensive chemicals and helping the insects to overcome host tree defense. Streltzoviella insularis (Lepidoptera: Cossidae) is one of the most common woodborers in China, attacking various hosts, including ash trees ( Fraxinus spp.). Little is known about the role of gut bacteria of S. insularis and wheather they participate in overcoming tree chemical and structural compounds. In this study, we isolated gut bacteria of S. insularis larvae, analysed their ability to degrade pinoresinol (a candidate ash tree defensive compound) and cellulose, and identified pinoresinol degradation products. We found that larval mortality increased with increasing pinoresinol concentration (reflect in natural variation observed in the host trees). Pinoresinol also significantly degreased larval weight without such dose-dependency effect. Gut bacterial cultures identified five major bacteria, all of which were able to degrade pinoresinol, including two isolates that were also capable of cellulose degradation. Investigation of pinoresinol degradation suggested that pinoresinol degradation products may enter gluconeogenesis pathways, and may therefore result in production of carbohydrates for the larva or its gut microbiota. These results suggest that S. insularis associated microorganisms help to overcome host pinoresinol defence and possibly contribute to incets nutrition via carbohydrate synthesis.