Varroa destructor rearing in laboratory conditions: importance of foundress survival in doubly infested cells and reproduction of laboratory-born females

A considerable part of the knowledge about the honey bee parasite Varroa destructor emerged from rearing protocols in semi-natural or laboratory conditions, yet a durable protocol over several generations of mites is still lacking. The development of such multigenerational rearing relies on the emergence of a sufficient number of new fertile females in the first generation of V. destructor . The optimization of the parasite’s reproductive success in laboratory conditions thus represents an important prerequisite. The number of foundress mites in a cell is known to impact the probability of male survival and thus the number of mated daughters. We therefore investigated the effect of the degree of bee larvae infestation under laboratory conditions. The results showed that the probability of finding at least one foundress alive at the end of the rearing was significantly higher in doubly infested cells. This leads to the improvement of the reproductive parameters and more specifically of the number of daughters per mite. In doubly infested cells with one dead foundress, the presence of a surviving female would in fact allow both its descendants and those of the dead mite to complete their development. The mated daughters from this system were used in a subsequent experiment to test their ability to complete their reproductive cycle in laboratory conditions, from the perspective of developing a multigenerational rearing. The reproduction and development of the offspring measured were similar to those of the first generation. However, many of the females from the second generation died before the completion of their first reproductive cycle. We suggest that these females are fertile but might lack the energy necessary to survive throughout reproduction. The results from our bioassay could constitute a basis for the development of a durable V. destructor laboratory rearing and for the improvement of our understanding of the parasite’s reproductive cycle.