Coloured scanning electron micrograph (SEM) of a Varroa mite (Varroa destructor), showing the parasites extremely flat morphology.
Varroa destructor is an external parasitic mite that attacks honey bees (Apis cerana and Apis mellifera). The disease caused by the mite is called varroatosis.
The species was discovered in Java in 1904 and the man who described the mite named it Varroa jacobsoni, after the collector. Apparently, he could not imagine the enormous threat the mite would become some hundred years later. For a long time, this was of little interest to anybody. Within the species there is some morphologic diversity. Genetic studies in the late 1990s finally identified a second species within V. jacobsoni which is much more virulent to Honey bees and was therefore named V. destructor.
Varroa destructor reproduces in honey bee colonies. The image shows an adult female which are three times larger than adult males. The parasite attaches to the body of a bee and weakens the host by sucking hemolymph. In this process, RNA viruses such as the deformed wing virus (DWV) spread to bees. A significant mite infestation leads to the death of a honey bee colony. The Varroa mite is the world’s most devastating pest of Western honey bees.
Varroa mite life cycle has two stages. During the phoretic stage (5-11 days), mites ride on adult workers or drones, at the same time feeding on blood (hemolymph) from bees, usually from the inter-segmental membrane on the abdomen. Mites change hosts (hop from one bee to another) often and this contributes to transmission of various viruses.
The other stage is the reproductive stage. The mite invades a worker or drone larvae cell just before the cell being capped. Once inside, it hides in the brood food breathing with special appendages called “peretrimes” (i.e. snorkeling tubes). 70 hours after the bee cell was capped the mite starts to lay eggs. The first egg is not fertilized, and becomes a male while all other eggs are fertilized and become females. Usually, whatsoever, only one female can be produced during the larval development of a bee.