Impact of Varroa destructor on honeybee (Apis mellifera scutellata) colony development in South Africa.

The devastating effects of Varroa destructor Anderson & Trueman on European honeybee colonies (Apis mellifera L.) have been well documented. Not only do these mites cause physical damage to parasitised individuals when they feed on them, they also transmit viruses and other pathogens, weaken colonies and can ultimately cause their death. Nevertheless, not all honeybee colonies are doomed once Varroa mites become established. Some populations, such as the savannah honeybee, A. m. scutellata, have become tolerant after the introduction of the parasite and are able to withstand the presence of these mites without the need for acaricides. In this study, we measured daily Varroa mite fall, Varroa infestation rates of adult honeybees and worker brood, and total Varroa population size in acaricide treated and untreated honeybee colonies. In addition, honeybee colony development was compared between these groups in order to measure the cost incurred by Varroa mites to their hosts. Daily Varroa mite fall decreased over the experimental period with different dynamics in treated and untreated colonies. Varroa infestation rates in treated adult honeybees and brood were lower than in untreated colonies, but not significantly so. Thus, indicating a minimal benefit of treatment thereby suggesting that A. m. scutellata have the ability to maintain mite populations at low levels. We obtained baseline data on Varroa population dynamics in a tolerant honeybee over the winter period. Varroa mites appeared to have a low impact on this honeybee population, given that colony development was similar in the treated and untreated colonies.