Entomopathogenic fungi and the company they keep - Exoskeletal microbiomes of Dung beetles in Australia.

Dung beetles process a significant amount of livestock dung in Australia, thereby reducing livestock pests and
pathogen populations. When establishing in new environments, dung beetles face numerous challenges including infection by entomopathogenic fungi. Insect microbiomes have been shown to be important in exoskeletal defence and susceptibility to entomopathogens. We investigated the composition of exoskeletal microbiomes of introduced dung beetle species reared under field and controlled-environment conditions. We isolated and identified several species of entomopathogenic fungi from exoskeletal surface of dung beetles, and investigated the effects of temperature and light conditions on fungal growth and secondary metabolite production. Swabs from the exoskeletons of healthy and diseased dung beetles were cultured to investigate their respective exoskeletal microbiomes. Genomic DNA was extracted from fungal and bacterial culture plates, and identification of species composition was performed by sequencing ITS and 16SrRNA genes. Entomopathogenic fungi associated with diseased dung beetles were isolated, and were identified by sequencing of ITS, TEF-1 α, nrSSU, and nrLSU genes. Unique fungal isolates were further evaluated for production of toxic secondary metabolites. Results suggest a significant difference in the microbial diversity on the exoskeletal surfaces of diseased dung beetles in contrast to those of healthy dung beetles. Mass-rearing under controlled conditions significantly altered the composition of exoskeletal microbiome of healthy dung beetles. Entomopathogenic fungi frequently encountered on exoskeletal surfaces of diseased beetles were identified as Beauveria bassiana, B. pseudobassiana, and Samsoniella spp. Further investigation of unique fungal organisms prevalent on field-reared dung beetles identified microflora capable of producing toxic metabolites associated with entomopathogenicity.