Submitted to: Journal of Apicultural Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2005
Publication Date: 3/4/2005
Citation: Harbo, J.R., Harris, J.W. 2005. Suppressed mite reproduction explained by the behavior of adult bees. Journal of Apicultural Research. 44(1):21-23. Interpretive Summary: The varroa mite, Varroa destructor, is an external parasite of the honey bee and the number one problem in the beekeeping industry. The mites have become resistant to chemical treatments, and the long-term strategy for varroa control is to breed honey bees for resistance. Scientists at the Bee Breeding, Genetics and Physiology Laboratory in Baton Rouge have described and developed a natural trait of the honey bee that results in bee colonies that have a high frequency of mites that do not produce progeny. They called it the suppressed mite reproduction (SMR) because the mites in SMR colonies had a very low frequency of reproduction. The purpose of this study was to determine how bees are able to control mite reproduction in colonies with the SMR trait. Nine colonies with the SMR trait and 8 control colonies without the SMR trait were each given a comb of newly capped worker brood that was naturally infested with varroa. After 8 days in the test colonies, the mite populations in these combs were examined in capped cells that contained pupae that were 8 ' 11 days postcapping. Combs from SMR colonies had an average of 2.2% of their cells infested with mites, controls averaged 9.0%. Therefore, bees with the SMR trait apparently removed mites from capped cells. Of the mites that remained, the SMR colonies had a much higher rate of nonreproductive mites, 80% vs. 29%. This suggests that bees with the SMR trait removed reproductive mites more often than they removed nonreproductive mites. We think that by targeting the reproductive mites, bees with the SMR trait give the illusion that nearly all of the mites are nonreproductive. In reality, the number of nonreproductive mites probably does not change. By knowing the mechanism behind the SMR trait, bee breeders will be better able to select for this trait and to find and develop other mite resistance traits of the honey bee.
Technical Abstract: Suppressed mite reproduction (SMR) is a heritable trait of the honey bee (Apis mellifera L) that can control the parasitic mite, Varroa destructor. The purpose of this study was to determine whether or not adult bees with the SMR trait affect mites in brood after cells are capped. Colonies with or without the SMR trait were each given a comb of newly-capped worker brood that was naturally infested with varroa. Each of 7 source colonies provided a comb of brood to at least one SMR (n = 9) and one control colony (n = 8). These combs were removed from their host colonies 8 days later and mite populations were evaluated in cells with bee pupae that were >8 days post-capping. Colonies with SMR bees averaged 2.2% of their cells infested with mites, controls averaged 9.0%. Therefore, bees with the SMR trait apparently removed mites from capped cells. Of the mites that remained, the SMR colonies had a much higher rate of non-reproductive mites, 80% vs. 29%. This suggests that bees with the SMR trait removed reproductive mites more often than they removed non-reproductive mites. When comparing only the number of non-reproducing mites that had no progeny, the groups were almost identical averaging 1.2 and 1.3 mites per 100 cells of brood. This suggests that the SMR bees did not remove mites from brood cells if the mites did not lay eggs. By targeting the reproductive mites, bees with the SMR trait give the illusion that nearly all of the mites are non-reproductive. Therefore, our selection for a high frequency of non-reproductive mites may have produced bees that primarily remove reproductive mites from capped brood, not a condition that caused mites to be non-reproductive.