Microbiome assembly on body surfaces benefits the flies to combat fungal infections.

In contrast to the well-characterized gut microbiomes, the composition and function of the insect body-surface microbiotas are still elusive and highly underexplored. Here we report the dynamic features of the surface microbiomes. It was found that the microbiomes assembled on fly surfaces could defend insects against fungal parasitic infections. The substantial increase of bacterial loads occurred within 10 days of fly eclosion, especially the expansion of species. The culturable bacteria such as could effectively inhibit fungal spore germinations, and the gnotobiotic addition of the isolated bacteria could substantially delay fungal infection of axenic flies. We found that the fly tarsal segments were largely accumulated with bacterial cells, which could accelerate cell dispersal onto different body parts to deter fungal spore germinations. Our findings will facilitate future investigations of the surface microbiotas affecting insect physiologies.