Wireworm-Associated Microbial Communities and their Implications on Biological Control.

Wireworms (larvae of different click beetles, Elateridae) are significant soil-borne pest species that can cause severe crop losses. They are difficult to control, and biocontrol using entomopathogenic fungi (EPF) display variable field efficacy. To understand microbial interactions and improve biological control, we studied the interplay between insect and soil microbiota in four wireworm species (Agriotes spp.) at temporal and spatial scales. We found that microbiota associated with wireworms are species-specific and primarily soil-derived. Our results further indicate that ectosymbiotic bacterial community composition on wireworm cuticles is relatively stable over time in specimens not deceasing from spontaneous entomopathogen infection. Therefore, successful microbiome homeostasis on cuticles appears to be correlated with long-term survival of wireworms in soil. Interestingly, EPF were prevalent but low-abundant in all wireworm species as well as in soils. Therefore, we analyzed immune priming effects by low-abundant EPF in soil. Mortality was higher in naïve wireworms than in wireworms pre-exposed to EPFs, and molting frequency increased, indicating both developmental adaptations and immune priming as strategies for EPF avoidance in wireworms. This work disentangles the key components of wireworm microbiomes and highlights the importance of microbial interactions for biocontrol. Biocontrol of wireworms could be improved by considering their species-dependency in microbiome homeostasis as well as physiological and behavioral adaptations to soil-borne pathogens. The potential functional synergies between EPF and soil microbes need further exploration.