Submitted to: American Bee Journal
Publication Type: Trade journal
Publication Acceptance Date: 6/10/2005
Publication Date: 9/1/2005
Citation: DeGrandi-Hoffman, G., Curry, R. The population dynamics of Varroa mites in honey bee colonies: Part III - How beekeeping practices could affect Varroa populations. Amer. Bee J. 2005. Vol. 145(9):709-710. Interpretive Summary: The reproductive rate of foundress female mites greatly impacts Varroa population growth and honey bee colony survival. We conducted simulations with the VARROAPOP program using colonies inititally infested with 2000 Varroa on April 1. The colony survived for 3 years without miticide treatments when the reproductive rate of Varroa was set at 1.2 mated females per foundress. If the reporductive rate was increased to 1.5, the colony died in about 18 months. Colonies survived for less than one year in sumulations where the reproductive rate of foundress females was increased to 1.7 mated females. We theorize how the distribution of colonies in commerical apiaries could select for Varroa with higher reproductive rates. In feral populations, mites disperse when colonies swarm. Only strong colonies swarm, so selection would favor mites with lower reproductive rates. Unlike feral bee populations where colonies can be widely separated, apiaries have many colonies in close proximity. Colonies weakened by Varroa are found and robbed. The mites disperse to other colonies in the apiary on the robber bees. In apiaries, selection would favor mites with higher reproductive rates. How beekeeping practices and the distribution of colonies in apiaries can affect mite reproductive rates and dispersal strategies are discussed.
Technical Abstract: VARROAPOP simulations were conducted to determine the effects that slight changes in genetically inherited characteristics of Varroa have on their virulence. Reproductive rates of foundress female mites in worker brood cells were increased from 1.2 mated female mites to 1.5 and 1.7. Colonies initially infested with 2000 Varroa on April 1 survived for 3 years without miticide treatments when the reproductive rate of Varroa was set at 1.2 mated females per foundress. If the reproductive rate was increased to 1.5, the colony died in about 18 months. Colonies survived for less than one year in simulations where the reproductive rate of foundress females was increased to 1.7 mated females. How Varroa dispersal strategies differ between feral colonies and managed apiaries is discussed. Dispersal of mites on swarming bees would be selected for in feral populations since colonies usually are widely separated and movement of bees between colonies is limited. Only large colonies swarm, so selection would favor lower mite reproductive rates. In commercial apiaries, many colonies are placed close together so bees can find and rob those weakened by Varroa. The mites will disperse by attaching on to the robber bees. In apiaries, selection would favor mites with higher reproductive rates that would weaken colonies and cause mite dispersal on robbing bees.