Varroa mites were first discovered in the United States in 1987, and then the mites were detected in North Carolina three years later. The mites have since spread throughout the rest of the country. They are considered to be the most serious pest of honeybees worldwide. Infested colonies will die within 1 to 2 years unless the beekeeper takes the necessary actions to rid the colony of the mites.
The Varroa mites are external parasites of the drone and worker bees. They prefer drones, but will infect the workers also. Varroa mites are visible with the naked eye and look somewhat like a tick. The mated female moves into a brood cell with older bee larvae. Mites will feed on the larvae food or puncture the larval body and feed on the bee's blood. The mated female mite will lay an egg every 36 hours on the side of the cell. The first egg will be unfertilized and develop into a male. The other eggs are fertilized will hatch into females. The young mites feed on the developing pupa. The young females will then mate with the male and emerge from the cell when the bee emerges. The female mites will then enter another cell or attach themselves to an adult bee to feed on. The Varroa mites are transported from colony to colony by drifting or robbing bees.
There are visible symptoms of the damage from the mites on the newly emerged bees, which is due to the mites feeding on the immature bee in the cell. The newly emerged bee will be smaller than normal, have crumpled or disjointed wings, and shortened abdomens. The life span of the infected bee is also shortened. Severe infestations from the mite within the cell, which is several mated adult female mites in one cell, can cause death to the pupa. Other symptoms of mite infestations are the rapid decline of the colony, reduced adult bee population, evacuation of the hive by crawling bees, queen's lack of performance, spotty brood, and abnormal brood.
Detection is the first step to control. There are methods used to detect the presence of the Varroa mites as follows:
Extract drone brood when present and visually examine larvae and cells for mites. There are visible against a light colored background.
Fill a quart jar about 1/4 full of live bees. Cover and insert a 2-second blast from an aerosol ether-based engine starter fluid or aerosol oil cooking spray. Shake the jar for 20 seconds. Turn the jar on its side and rotate slowly and look for mites clinging to the sides of the jar. If you do not spot any mites, remove the bees and rinse in alcohol. Shake and remove the bees so you can examine the alcohol.
The best and most reliable method is to use Apistan@ (fluvalinate) strips or US: Check Mite+ strips.. Place a piece of waxed or white paper sprayed with aerosol oil cooking spray and covered with 8-8 squares/inch of mesh wire on the bottom board. Insert strips according to label directions. Check the paper in one hour. If there are no mites, check again the next day.
You can request a free inspection from you local NCDA bee inspector.
Never treat during a nectar flow because the chemicals can contaminate the honey and never leave strips in hives after the recommended time this can cause sublethal doses of the chemical. However, if mites are detected, you may need to treat to save your colony.
In recent years mite have become resistant to Apistan strips and has become a problem throughout the world. Therefore, rotating chemical, delaying treatment and using cultural control are recommended to manage mites in a more bearable fashion.
Delaying treatment can be accomplished if you monitor the level of Varroa mite infestation in your colonies. There are ways to check the colony for the number of mites present. Knowing the level of infestation in your colonies will help you determining whether treat is required immediately or if it can wait until after the nectar flow season has passed.