Symbiotic bacteria on the cuticle protect the oriental fruit moth Grapholita molesta from fungal infection

Abstract

The oriental fruit moth, Grapholita molesta (Lepidoptera: Tortricidae), is a destructive orchard pest native to the Asian subcontinent that has spread throughout many fruit-growing regions of the world. The entomopathogenic fungus Beauveria bassiana (Balsamo-Crivelli) Vuillemin (Hypocreales: Cordycipitaceae) is widely employed for control of insect pests, including G. molesta. Various studies have shown that microorganisms present on the insect cuticle can inhibit fungal spore germination and growth, thus inhibiting their pathogenicity and biological control efficacy. We conducted bioassays on larvae pre-treated with antibiotics to test whether cuticular microbiota could reduce the pathogenicity of B. bassiana to G. molesta. Control larvae (untreated with antibiotics) had higher survival than antibiotic-treated larvae following inoculation with B. bassiana, indicating that cuticular microbiota inhibited infection of G. molesta by B. bassiana. The bacterial diversity present on the cuticle of G. molesta larvae was characterized by 16S rDNA amplicon sequencing. The dominant bacterium isolated was Pantoea sp. and its antagonism toward B. bassiana was assayed in vitro using the inhibition zone method. Inhibitory effects on the pathogenicity of Pantoea sp. against B. bassiana were demonstrated by reintroducing the bacterium to G. molesta larvae that had been pre-treated with antibiotic, which increased their survival in comparison to antibiotic-treated larvae following inoculation with B. bassiana. This study provides potentially valuable insights for maximizing the efficacy of B. bassiana applications for biological control of G. molesta.