Cleaner mites: sanitary mutualism in the miniature ecosystem of neotropical bee nests.

Cleaning symbioses represent classic models of mutualism, and some bee mites are thought to perform cleaning services for their hosts in exchange for suitable environments for reproduction and dispersal. These mutual benefits, however, have not been rigorously demonstrated. We tested the sanitary role of bee mites by correlating mite loads with fungal contamination in natural nests of Megalopta genalis and Megalopta ecuadoria and by experimentally manipulating mite loads in artificial cells with developing brood. Field observations revealed significant correlations between the presence of mites and the absence of fungi inside the brood cells, as well as between the absence of mites and increased bee mortality. Likewise, experimental brood cells with mites have fewer fungal colonies than do cells without mites. Field observations and experimental manipulations, therefore, provide clear evidence of the sanitary effect of mites in nests of Megalopta bees. This bee-mite association constitutes one of the few examples of terrestrial cleaning mutualisms.