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Integrated Pest Management for Varroa Destructor in the Northeastern United States using Drone Brood Removal and Formic Acid

a mature adult female V. destructor
Photo A. A mature adult female V. destructor.
Geographic Range: Northeastern U.S.
The methods discussed in this fact sheet were developed and evaluated in the northeastern U.S. Drone brood removal will benefit beekeepers throughout the U.S.; however, formic acid and other miticides acting as fumigants work best in areas where colonies are broodless or nearly broodless for at least four weeks during the fall or winter. When a colony is rearing brood, most mites are present in brood cells where they are protected from the effects of fumigants. During broodless periods, mites are present on adult hosts and are susceptible to fumigants. Since fumigants have a relatively short treatment period (about three weeks) compared to other pesticides (about six weeks), it is critical that the majority of mites be present on adult hosts for fumigants to be effective.

Introduction
This bulletin focuses on the management of the parasitic honey bee mite Varroa destructor (V. destructor) in the northeastern U.S. It contains information that will allow a beekeeper to: 1) identify V. destructor, 2) recognize the symptoms of mite infestation, 3) determine pest densities, and 4) implement an effective IPM program for keeping mite populations below the economic injury level.

The western honey bee, Apis mellifera, was introduced to the U.S. from Europe in the 1600s. Today, the honey bee provides essential pollination services for over 45 commercial crops grown throughout the U.S., adding $14.6 billion to the value of the country's agricultural production each year. In addition, U.S. beekeepers produce between 170 and 220 million pounds of honey each year, more than 50% of total U.S. consumption. Hence, a sustainable supply of healthy and affordable honey bee colonies is a critical factor affecting farm productivity and the stability of farm incomes and food prices.

The parasitic honey bee mite V. destructor (photo A) is considered to be the most serious global threat to beekeeping and to the sustainable production of crops that rely on A. mellifera for pollination. V. destructor, which kills honey bee colonies of European descent within one to two years, has killed millions of managed and wild colonies in the U.S. in the past two decades. Apistan® and CheckMite+® have provided some relief, but control always has been unpredictable due to the fact that mite populations often rise rapidly during the honey-producing season, when treatment is proscribed by label restrictions. Consequently, colonies often suffer serious damage while the beekeeper waits for a legal treatment window to open. The threat from V. destructor has become a matter of grave concern as resistance to both Apistan® and CheckMite+® has become widespread.

To continue to be viable, the beekeeping industry requires sustainable management practices that will keep mite populations below the economic injury level and maintain the high quality of hive products. The best way to achieve these goals is to use a management program that relies on multiple tactics, rather than solely on chemicals. One such approach is referred to as Integrated Pest Management or IPM. IPM incorporates chemical and non-chemical tactics; however, for several reasons, IPM minimizes the use of chemicals whenever possible. First, chemicals add a recurring cost to a beekeeper's management program. Second, chemicals inevitably show up as residues in hive products, and that jeopardizes their reputation as pure and natural products. Third, chemicals can be injurious to the applicator and may pose a risk to the consumer. This raises the issue of liability, especially for beekeepers with employees. Fourth, the less a pest population is exposed to a pesticide, the more slowly it develops resistance to that pesticide. So, by minimizing the use of a pesticide, its useful lifetime is extended.

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