Gut Bacteria of Wood-Boring Streltzoviella insularis and Their Involvement in Pinoresinol Degradation of Ash Tree (Fraxinus sp.) Host

Insect gut microbiota have been widely reported to helpthe insectsto overcome host tree defense. Streltzoviella insularis (Lepidoptera: Cossidae) is one of the most common wood borers inChina, attacking various hosts, including ash trees (Fraxinus sp.), but little is known about its gut microbial associates andtheir involvement in host tree defense. We isolated gut bacteria of S. insularis larvae, analyzed their ability to degradepinoresinol (a defense compound of ash trees) and cellulose, and identifiedpinoresinol degradation products. Larval mortality increased withincreasing pinoresinol concentration (reflecting natural variationobserved in the host trees). All the five detected gut bacteria isolateswere able to degrade pinoresinol, two of which were also capable ofcellulose degradation. Furthermore, gut bacteria were also shown todegrade pinoresinol via the gluconeogenesis pathway. These resultssuggest that S. insularis-associatedmicroorganisms help to overcome host pinoresinol defense and possiblycontribute to insects or gut microbial nutrition via carbohydratesynthesis.