ABRC2010 Effects of Varroa Mites and Bee Diseases on Pollination Efficacy of Honey Bees

The following was presented at the 2010 American Bee Research Conference in Orlando, FL.

1. Afik, O., W.B. Hunter & K.S. Delaplane – EFFECTS OF VARROA MITES AND BEE DISEASES ON POLLINATION EFFICACY OF HONEY BEES – Varroa mites and viral diseases are known to affect the efficiency of crop pollination by honey bees through the elimination of colonies, but only limited information exists on their influence on pollination at sub-lethal levels on the individual bee (Ellis & Delaplane, 2008 Agr. Ecosyst. Environ. 127:201-206). The purpose of this study was to learn about effects that varroa mites and bee diseases may be having on the foraging behavior of adult bees and the consequences of these effects on successful fruit pollination. For the first season of the experiment, four honey bee colonies of about 4,500 bees each were established. Two of these colonies were each infested with 1,000 varroa mites collected from other hives by sugar powdering. Two other colonies were used as non-infested control colonies. In order to force mites to attach to the adult bees, brood combs from both treatments were replaced with empty combs before brood was sealed. 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. Each visiting bee was collected at the end of the flower visit and preserved for later pathogen analysis.

The 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. Bees from infested colonies performed shorter flower visits and a lower percentage of them were pollen foragers. These two behavioral differences may contribute to lower rate of fruit-set since the duration of flower visit was positively correlated with pollen deposition and pollen foragers were found to be more efficient pollinators of blueberry flowers than nectar foragers. More than 75% 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 spp., ABPV, IAPV or KBV. The results suggest that bees from colonies highly infested with mites are less efficient pollinators, possibly due to shorter visits to the flowers and lower tendency to collect pollen. 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.

More presentations from this conference can be found at Proceedings of the American Bee Research Conference 2010