Varroa Destructor - Reproduction, Infection and Hive Mortality

Reproduction, Infection and Hive Mortality

Mites reproduce on a 10-day cycle. The female mite enters a honey bee brood cell. As soon as the cell is capped, the Varroa mite lays eggs on the larva, which hatch into several females and typically one male. The young mites hatch in about the same time as the young bee develops and leave the cell with the host. When the young bee emerges from the cell after pupation, the Varroa mites also leave and spread to other bees and larvae. The mite preferentially infests drone cells.

The adults suck the "blood" (hemolymph) of adult honey bees for sustenance, leaving open wounds. The compromised adult bees are more prone to infections. With the exception of some resistance in the Russian strains and bees with varroa-sensitive hygiene genes developed by the USDA, the European Apis mellifera bees are almost completely defenseless against these parasites (Russian honey bees are one-third to one-half less susceptible to mite reproduction).

The model for the population dynamics is exponential growth when bee brood are available and exponential decline when no brood is available. In 12 weeks, the number of mites in a western honey bee hive can multiply by (roughly) 12. High mite populations in the autumn can cause a crisis when drone rearing ceases and the mites switch to worker larvae, causing a quick population crash and often hive death.

Varroa mites have been found on flower-feeding insects such as the bumblebee Bombus pennsylvanicus, the scarab beetle Phanaeus vindex and the flower-fly Palpada vinetorum. Although the Varroa mite cannot reproduce on these insects, its presence on them may be a means by which it spreads short distances (phoresy).