Varroa Life Cycle

Originating from southeast Asia, Varroa mites have spread to most of North America and pose a significant threat to the health of honey bee populations. Varroa mites are an ecto-parasite of many bee species, attaching themselves to both immature and adult bees and feeding on their hemolymph, or blood. The life cycle of Varroa mites is directly tied to the life cycle of honey bees. Understanding how Varroa reproduce is important in knowing how to detect and manage them.

  1. Description

    • Varroa mites resemble tiny crabs with flat, oval bodies. Adult female mites are reddish-brown and about 1.5 millimeters long and 1.75 millimeters wide. Male mites are yellow and have a round body that is smaller than the female. Well adapted to it's host, the curved body of the Varroa mite fits well into the body segments of the adult bee, protecting it from the being removed during grooming.

    Preparation

    • First, the pregnant adult female Varroa mite attaches itself to an adult worker or drone bee. It then cuts into the membrane between the body segments and begins feeding on the bee. This allow the eggs within the mite to grow sufficiently until it is time to lay them.

    Move to brood

    • When ready to lay it's eggs, the female Varroa mite drops off the host bee, and proceeds to an uncapped brood cell within the hive. The mite selects a cell that has a recently hatched bee larva. There, it sneaks between the bee larva and the cell wall and hides in the brood food or jelly and waits for the cell to be capped by a worker bee, trapping it within the cell. Eventually the mite consumes all of the brood food. Once the brood food is gone, the female mite will then feed on the bee larvae itself.

    Egg laying and metamorphosis

    • Within the enclosed brood cell, the female mite will lay several eggs that hatch into larvae. The first egg laid will be a male egg. The female does not lay all eggs at the same time, but stages the process at 30-hour intervals to allow for more mites to develop over the brood cycle. Varroa mites seem to prefer laying eggs in drone cells, due to the increased cell size and longer development time of drone larvae compared to worker bee larvae. Two days after hatching, the mite larvae become protonymphs. After sufficiently feeding on the bee larva, they will molt to become deutonymphs. After three more days, they go through their final molt to adulthood.

    Mating and adulthood

    • Twenty-four hours after the mites mature, they mate inside the capped brood cell. The male then dies in the cell. When the bee larva matures and exits the brood cell, the adult mother mite and any of her surviving daughters emerge. They then attach themselves to other worker or drone bees, feeding on them until the time comes to lay their eggs and start the cycle again.

    Diagnosis

    • Varroa mites can be detected through direct observation. One method, called an ether roll, requires collecting between 300 and 500 bees in a pint jar. Then ether-based starter fluid is sprayed on the bees for about two seconds. The jar is closed, then shaken and rolled back and forth. Mites will be seen sticking to the inside of the jar. Unfortunately this method is fatal to the bees. A similar technique using powdered sugar instead of ether can be used without harming the bees. Sticky paper can also be placed on the bottom of a hive under #8 hardware cloth to collect and observe falling mites.

    Treatment and management

    • The miticides Apistan® and CheckMite+®, plastic strips impregnated with fluvinate or coumaphos are now approved for controlling Varroa mites. If the colony is not heavily infested, treatment with either medication will last for one year. Mites will eventually build up a resistance to these treatments and alternatives are currently being researched. Before using chemical treatment for mites, first determine the level of infestation. Also be sure to continually monitor the progress of the treatment.

      Varroa mites cannot be completely eradicated once a colony is exposed. Managing the infestation is currently the only known solution to the problem. Keeping mite counts down will allow the bees to survive and thrive.