Reproductive biology of varroa mites in colonies of Africanized honey bees

Abstract

We investigated the reproductive biology of V. destructor in Africanized honeybees (AHB) in Central American conditions, specifically in Costa Rica. Attention was paid to mite fertility and production of viable female mites in worker and drone brood cells. Other reproduction parameters, like fecundity, production of only immature offspring, production of only female or only male offspring and no reproduction at all are discussed. Furthermore, results on mite population dynamics and its influence in the colony condition are presented. We hypothesized that, due to the preference of mites to invade drone brood to reproduce, a high proportion of the mite reproduction in Africanized bees should occur in drone cells. Mite fertility for varroa infesting worker brood cells in AHB in Costa Rica, ranged between 69% and 76%. So the number of fertile varroa mites in worker brood was higher than what other studies have reported for AHB in Brazil. Nevertheless, factors that limited varroa reproduction in worker brood were the non-reproducing mites, foundresses that produced only immature stages, foundresses that produced one adult sex, mortality of emerging mites and the absence of the male we found in a considerable percentage of worker cells. The combined effects of these factors results in less than 30% of the foundress mites producing viable female in Africanized colonies. The absence of the male in worker cells reduces the production of viable daughters. We observed in artificial cells containing infested worker brood in Africanized bees that in a considerable number of cases the first egg (that is generally male ) was disturbed and damaged when the prepupa molts into a pupa. We consider that the absence of male in a considerable number of worker cells could be hypothesized by this effect. The low number of viable females produced by foundress mites found in worker brood cells of AHB colonies, seems insufficient to explain the occurrence of viruses in severely infested colonies and the mite infestation increase in the colonies through the year. Due to the preference of mites to infest drone brood to reproduce, we compared the reproductive rate of V. destructor in worker and drone cells of AHB colonies. We found that mite fertility was similar between worker and drone brood. However, one of the most significant differences in mite reproduction was the higher percentage of mites producing viable offspring in drone cells compared to worker cells. The number of eggs and viable females produced per foundress mites was also higher in drone brood. Furthermore, a high percentage of the non-reproducing mites in worker brood produced offspring when they were transferred to drone brood. This indicates that drone brood cells proved to be better suited for mite reproduction than worker brood cells and that brood type has an influence in the reproductive success of varroa mites in Africanized bees. The number of viable female offspring produced by invading mother mites depends, in part, upon the type of cell the mite enters, whether it is worker or drone Because in tropical conditions worker brood rearing takes place all year-round, varroa can completes many reproductive cycles. So the number of mite reproductive cycles that occurs in worker brood through the year and the successful reproduction of varroa mites in drone brood are significant factors related with the mite population growth determined in AHB colonies in Costa Rica.