Evidence for fungivory in Proctotydaeus furnarius, a brood mite of the Australian stingless bee Tetragonula carbonaria

Mites are common but poorly understood associates of stingless bee nests. The brood mite Proctotydaeus furnarius inhabits brood cells of Tetragonula carbonaria and was hypothesised to feed on fungi. We tested this hypothesis using electron microscopy, ITS amplicon sequencing, dye-based feeding trials, and brood-cell culturing. The unarmed, needle-like stylets of P. furnarius resembled those of fungivorous mites. In feeding trials, P. furnarius consumed a yeast isolate (Zygosaccharomyces sp.) cultured from brood cells, although also consumed crushed bee pupae. Mite presence did not detectably alter the culturable brood-cell microbial community. These findings suggest that P. furnarius feeds on fungi inside host nests but could shift its diet to feed on host brood according to resource availability.