Varroa destructor originally adapted to exploit the Asian honey bee (Apis cerana), It has in more recent decades adapted to using the European honey bee (Apis mellifera) as its host. Varroa mites feed on bee larvae and adult bees. These external parasites also spread viruses, wreaking further havoc in the hive.
As well as a decline in the population of the colony, Varroa destructor can result in deformed pupae and adult bees. Varroa is most attracted to drone brood and if present, you should be able to see them against the white background of the pupae.
Infestation will also lead to deformities in the pupae as well as adult bees. In adults, look for stunting and damaged wings, abdomens and legs.
Colonies with Parasitic Mite Syndrome will rapidly dwindle and die. A sure sign your colony has been struck lies in the condition of the larvae. Hygienic bees will chew down affected larvae and they will appear sunken to the wall of the cell. Larvae may be an unusual colour if decomposition has set in.
Adult females are a rusty red-brown and measure 1-1.8 mm (around 1/16 inch) in length and are slightly wider. They are round and shaped to fit snugly into the honey bee’s abdominal folds. Although tiny, they can be seen with the naked eye, especially when against a light coloured background, such as drone brood.
The Varroa mite's life cycle has two phases. The first is known as the phoretic phase. During this phase, mites will ride on adult workers and drones feeding on their bodily fluid. If there is brood for the mites to parasitise, this phase lasts 5-11 days. Otherwise, it can last as long as 6 months, during which the mites will spread disease as they hop from host to host. The mites then move onto brood as they enter their second, reproductive phase. After entering the cell, they move underneath the larva to feed on prepupa. The female lays her first egg 60 hours after the cell is capped, then one every 30 hours. Up to a half dozen will reach maturity within a week, feeding on the bee, impeding its development, and exposing it to disease. They mate, then adult females will leave the cell with the damaged bee, transferring to other bees, and the cycle begins again.