Effects of varroa mites and bee disease on pollination efficacy of honeybees

Authors: AFIK, O - University Of Georgia; Hunter, Wayne; DELAPLANE, K - University Of Georgia

Submitted to: American Bee Research Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 12/29/2009
Publication Date: 1/12/2010
Citation: Afik, O., Hunter, W.B., Delaplane, K.S. 2010. Effects of varroa mites and bee disease on pollination efficacy of honeybees. Proceedings American Beekeeping Federation Annual National Beekeeping Conference, January 12-16, 2010,Orlando, Florida. American Bee Journal 150(5): 497

Interpretive Summary: Varroa mites and viral diseases are known to affect the efficiency of crop pollination by honey bees through the elimination of colonies, but almost no information exists about their influence on pollination at sub-lethal levels. In order to address this issue we established four honey bee colonies, two of them heavily infested with Varroa mites at a ratio of 1:4.5 mites per bee. Each colony was caged in a separate enclosure containing one blueberry target plant and two potted pollen source plants. Pollination efficacy was tested by measuring percent of fruit-set and pollen deposition at flowers exposed to a single visit by an individual bee. Our first year results indicated that bees from mite infested colonies achieved a lower percent of fruit set and tended to deposit fewer pollen grains on the flower stigma. They performed shorter flower visits, a parameter that was correlated with pollen deposition. The percent of pollen foragers, which are more efficient pollinators than nectar foragers, was also lower in the mite infested colonies. Foragers from infested colonies tended to carry fewer pollen grains on the body. Most of the bees from both treatments were determined to be naturally infected with the viruses DWV and BQCV but no bee was positive for Nosema, ABPV, IAPV or KBV. The results indicate that bees from colonies highly infested with mites are less efficient pollinators. The effects of mite infestation combined with high virus infections have not yet been determined. Further research will focus on how to limit the effects of Varroa mites on the foraging behavior and pollination success of honey bees.

Technical Abstract: Single-stranded RNA viruses cause disease and behavioral changes in many insects, especially honey bees. Varroa mites and viral diseases are known to affect the efficiency of crop pollination by honey bees by eliminating colonies, but almost no information exists about their influence on pollination at sub-lethal levels. In order to address this issue we established four honey bee colonies, two of them were heavily infested with live Varroa mites at a ratio of 1:4.5 mites per bee. Each colony was caged in a separate enclosure containing one blueberry target plant and two potted pollen source plants. In order to encourage mites to attach to the adult bees, all brood combs from both treatments were replaced with empty combs before brood were sealed. Pollination efficacy was tested by measuring percent of fruit-set and pollen deposition at flowers exposed to a single visit of an individual bee. Our first year results indicated that bees from Varroa-infested colonies achieved a lower percent of fruit set and tended to deposit fewer pollen grains on the stigma of flowers visited. They also performed shorter flower visits, a parameter that was correlated with lower pollen deposition. The percent of pollen foragers, which are more efficient pollinators than nectar foragers, was lower in the infested colonies. Only four foragers were found with a Varroa mite on their body while visiting a flower, all of them from infested colonies, and these tended to carry fewer pollen grains on the body. Most of the bees from both treatments were infected with the viruses: DWV and BQCV, but no bee was positive for: Nosema, ABPV, IAPV or KBV. The effects of mite infestation combined with high virus infections have not yet been determined. Further research will focus on how to limit the effects of Varroa mites on the foraging behavior and pollination success of honey bees.