Understanding the Enemy: Genetics and Behavioral Ecology of Varroa destructor, the Parasitic Mite of the Western Honey Bee, Apis mellifera

Abstract

Varroa destructor is a cosmopolitan ectoparasitic mite that causes extensive detrimental effects on its new host Apis mellifera, The Western honey bee. Problems associated with Varroa parasitization include lower body weight, decreased learning capacity, lower stinging threshold, and shorter longevity. Varroa mites feed on the fat body tissue of developing and adult bees, and are also highly effective vectors of several honey bee-associated viruses, which can cause colony failure within a couple of years if no treatment is implemented. Beekeepers mainly rely on pesticides to lower the mite levels within colonies. However, most mite populations are now resistant to commonly used miticides, which is problematic because Varroa continues to wreak havoc on most beekeeping operations in the United States and around the world. The focus of this dissertation was to further understand the behavioral ecology of the Varroa mite, filling in the gaps in knowledge to better deal with this parasite. In the first research chapter, I found that honey bee worker larvae at closer proximity to drone brood did not have a higher risk of cell invasion by Varroa, but had a lower risk of cell invasion when they were on a frame with a high number of drone larvae. In the second research chapter, I did not find a clear link to between nurse visitation rates toward larval cells and an increased invasion of larval cells by Varroa. However, by experimentally increasing nurse visitation rates of worker brood after a 2-hr or 4-hr period of food restriction. I showed that precluding larvae from being fed for a given time period led to increased mite cell invasion later on. In the last research chapter, I measured the genetic diversity of Varroa mite populations across five states in the United States. I found clear differences in the genetic structure of mite populations between states and between apiaries. The results from this genetic study could be expanded further to understand whether certain genetically unique Varroa populations in the U.S. are more prone to being resistant to miticides, which could help us improve management methods to control this pervasive honey bee parasite.