Insect herbivore salivary glucose oxidase is associated with reduced carposphere microbial abundance

Microbial communities are essential to plant health, yet the mechanisms by which insect herbivores influence these communities remain unclear. Herbivore salivary enzymes, such as glucose oxidase (GOX), may modulate microbial populations through antimicrobial properties or by altering plant defenses. Using Helicoverpa zea larvae and two host plants, bell pepper (Capsicum annuum) and soybean (Glycine max), we investigated the role of salivary GOX in shaping microbial communities on fruit surfaces. CRISPR-Cas9 mutagenesis was employed to generate GOX-deficient mutants, and we assessed larval performance and microbial abundance on fruits. Wild-type larvae exhibited higher growth rates on artificial diets and bell pepper fruits compared to GOX-deficient mutants, indicating potential fitness costs to the larvae associated with GOX deficiency. Fruits attacked by wild-type larvae also harbored significantly lower microbial abundance, particularly on soybeans, suggesting that GOX reduces microbial populations either directly or indirectly through plant-mediated effects. These findings underscore the dual role of GOX in modulating plant-associated microbial communities and enhancing herbivore fitness. This study is the first to demonstrate that herbivore salivary GOX modulates carposphere microbial communities, revealing a novel mechanism by which insect herbivores influence plant-associated microbiomes. These findings highlight the ecological importance of herbivore salivary secretions and call for further research across diverse insect feeding guilds to assess implications for plant health, pathogen dynamics, and sustainable agricultural practices.