Temporal variation in colony immune response following infestation with an ectoparasitic mite

Background/Question/Methods The honey bee, Apis mellifera, and its parasite, the ectoparasitic mite Varroa destructor, have received much recent attention due to the mite's possible role in Colony Collapse Disorder, and as a vector of several lethal viruses, including Deformed Wing Virus (DWV). The prevalence of Varroa infestations changes with honey bee density, peaking during the summer months when the colony is at its strongest, but as yet no research has traced the effect of this temporal variation on the host immune response. As the threat of Varroa cycles annually with the bee population, it may be adaptive for bees to up-regulate their immune response as the season progresses, in line with increasing Varroa infestation levels. In this study, measures of the immune response were recorded over a six-month period in honey bee colonies experiencing different levels of Varroa infestation. The impact of the physical deformities associated with the transmission of DWV on the host's immune system was also investigated. Results/Conclusions Results suggest that colony investment in immune responses varies temporally, and is positively correlated with an increased threat of parasitism by Varroa. Where the threat of parasitism was absent, the investment in costly immune responses was scaled down. Physical deformities, indicative of DWV, were found to have a negligible effect on the immune response in a Varroa-infested colony. Colonies where Varroa were artificially removed using pesticides during the investigation period resulted in variation in colony immune responses. Given the prevalence of Varroa in colonies worldwide, the variation in defence strategies seen in the parasitised colonies highlights the issue of single colony use as a representative sample of the honey bee population as a whole. Due to the relatively recent introduction of Varroa and DWV to many countries, the study of this system as a model for host-parasite interactions is still in its infancy, but is no doubt of both great scientific and economic importance.