Parasitic Varroa mites (<i>Varroa destructor</i> Anderson & Trueman) are the most serious pest threatening the survival of honey bee colonies. Mite populations increase as colonies expand during the spring and summer. However, in the fall, mite numbers can rise sharply even in colonies with low mite infestations due to the migration of mites into colonies on foragers. If mite migration causes Varroa populations to grow rapidly, do levels of viruses transmitted by Varroa, particularly Deformed Wing Virus (DWV), also increase thus affecting overwintering survival? Can low virus levels be maintained by optimizing nutrition? To address these questions, we established colonies with low mite numbers in the early summer. Half of the colonies were fed pollen throughout the study and half were nutritionally stressed. Colony size, vitellogenin levels, mite numbers, virus titers, and the frequency of capturing foragers with mites (FWM) at colony entrances were recorded from July to December. Our path analysis indicated that DWV titers were significantly correlated to both numbers of phoretic mites on adult bees and mite infestation levels in brood cells, and these were correlated to the frequency of capturing FWM. Levels of DWV were unaffected by supplemental feeding, possibly because FWM entered fed and unfed colonies at similar rates and transmitted both mites and DWV. Our study demonstrates difficulties in controlling both Varroa and virus levels in colonies especially in the fall, and in assessing the effects of pesticide exposure to overwintering survival in an environment where mites and viruses are moving among colonies.

Movement of Varroa mites and the spread of viruses they transmit among colonies: Challenges to quantification of pesticide effects

2019 Fall National Meeting

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