Hidden in plain sight: Varroa aggregate on adult drones of Apis mellifera

Abstract As a nearly universal rule governing parasitology, parasites form aggregated distributions where a minority of hosts are responsible for harboring a majority of the parasite burden in any given population. For 30 years ectoparasitic Varroa destructor mites are described as preferring non-reproductive female nurse bees of its host, Western honey bee, Apis mellifera , while otherwise largely leaving the distribution of Varroa undescribed. As a result, Varroa- vectored disease transmission dynamics, sampling methodology and research have largely been worker centric. For the first time we investigate the intracolony distribution and dispersal patterns of Varroa on sex and age cohorts of its honey bee host in natural colonies and in laboratory choice experiments, and demonstrate that Varroa overwhelmingly prefer young adult males (drones), over any other cohort. We show Varroa form highly aggregated distributions on the drone cohort early in the season when infestation levels are low, and distribute broadly onto the worker cohort later in the season when infestation levels are high. In 1978 Anderson and May first proposed the theoretical framework that parasites would have little destabilizing effect on the host population until the degree of aggregation was low, or approached a Poisson distribution. The distribution patterns of Varroa are in alignment with their theoretical work, and maybe the underlying mechanism responsible for historical losses of honey bee colonies observed over the last decade.