LIFE CYCLE OF VARROA

Numerous studies have pieced together the life cycle of the Varroa mite (Figure 4), but it has yet to be cultured artificially and many aspects of its complicated biology are unknown. The adult female leaves the brood cell and attaches to an adult worker or drone where she begins to feed by cutting a hole in the intersegmental membrane of the bee's hard outer skeleton. Little is known about the length of time required for this phase. Next, the well-fed female drops off the adult into a brood cell and hides in the brood food (jelly).

Normally, once the brood food is consumed by the host, the female then begins to feed on the larvae itself by piercing its delicate skin. She then lays a number of eggs of both sexes which hatch into six-legged larvae. After 48 hours, these become eight-legged protonymphs which, after feeding on the bee larva, molt into a deutonymph. Three days later, the last molt to an adult occurs. Approximately twenty-four hours later the mites mate inside the capped honey bee brood cell. The males die after copulation in the brood cell and the female mites emerge to begin the cycle again.

The female mite does not lay its eggs all at once, but at prescribed intervals (See Figure 4). This means that the longer the brood cycle, the more time there is for subsequent mites to develop. It is thought that drones are preferentially parasitized because their developmental cycle is longer (24 days) than that of the worker (21 days). It is also believed that bees with shorter developmental times [Apis mellifera scutella, the African honey bee, and the Asian bee, Apis cerana (Indica)] are more resistant to Varroa because mite populations do not develop as quickly as in the European races.