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Tuesday, May 23, 2017

BIOLOGY OF THE VARROA MITE

The Varroa mite (Varroa destructor) is a parasite and therefore its biology is very closely connected with the life cycle of its host – the honey bee. The reproduction of the mites only takes place in capped brood.

Between two reproductive cycles, the adult female Varroa mites stay on the adult bees. Mostly, they sit between the ventral plates of the bees and suck the “bee blood” (hemolymph). They prefer nurse bees over forager bees, because of their close proximity to the brood.

To reproduce, female Varroa invade brood cells shortly before capping. Inside the cell, they hide at the bottom, lying on their back in the larval food. When the cell is capped and the larva has finished the food, the mite becomes free.
60-70 hours after cell capping the female Varroa lays its first egg on the wall of the brood cell, with subsequent eggs following every 30 hours. The first egg is not fertilized and develops into a male, while the following eggs are fertilized and therefore develop into females.

In total, the female Varroa lays 5-6 eggs, the last one about nine days after the cell capping. Not all these eggs develop into adult mites, because the time for their development is limited by the capping period of the brood cell.

The mating of the daughter mites also takes place within the capped brood cell, i.e. the males fertilize their sisters shortly after their last ecdysis when they become adult. When the bee emerges, only the mated adult daughter mites leave the brood cell together with the mother. All males and younger female instars die.

Life cycle

The life cycle of Varroa destructor (after Rosenkranz)

a  Invasion of the brood cell just before cell capping
 
b  Reproduction in the brood cell
 
c  Emerging of the adult bee with Varroa mites
 
d  Varroa mite on an adult bee