STARKVILLE, Miss. -- Entering this spring, beekeepers will be tasked with rebounding from the worst winter in over a decade for winter bee mortality.

A nonprofit organization, called Project Apis m., surveyed more than 700 U.S. commercial beekeepers and found they lost 62% of their colonies between July 2024 and February of this year.

The U.S. Department of Agriculture’s National Agricultural Statistics Service, or NASS, estimated more than 2.5 million hives were managed by beekeepers in the U.S. in 2024. Of that, 29,000 colonies of bees in Mississippi produced honey last year, not including colonies owned by northern U.S. beekeepers who winter their bees in the state.

Jeff Harris, apiculture specialist with the Mississippi State University Extension Service, said varroa mites -- the primary killers of honeybees -- have become more physically resilient since they were first reported in the U.S. nearly 40 years ago, which has led to the increased mortality numbers.

“It seems to be the typical story of a pest becoming resistant to the insecticide used to control it,” Harris said. “The insecticide is amitraz, and it is usually used in the form of a no-pest strip that is hung inside beehives to kill mites. We noticed that amitraz was no longer killing varroa mites here in Starkville beginning late summer 2024.”

Frank Rinkevich, research entomologist based at the USDA-Agricultural Research Service Honey Bee Breeding, Genetics and Physiology Laboratory in Baton Rouge, La., documented the resistance of varroa mites to amitraz in his study published in the Public Library of Science scientific publication PLOS One in 2020. He evaluated amitraz resistance in commercial beekeeping operations in Louisiana, New York and South Dakota with long histories of this acaricide’s use.

“Anecdotal reports of reduced amitraz effectiveness have been a widely discussed contemporary issue among commercial beekeepers.” Rinkevich said in the study. “Amitraz remains an effective Varroa control product in many operations. However, apiaries across operations displayed a wide range of amitraz resistance from no resistance to high resistance that resulted in Varroa control failure.”

Harris said what makes varroa mites so lethal to honeybees is the viruses they transmit to them – most commonly the Deformed Wing Virus. Mites feed on the bees’ bodies, mainly in the pupal stage during development into adult bees.

 “It is the viruses that ultimately kill a colony of bees,” he said. “Because we do not have antiviral drugs for honeybees, the best way to keep virus concentrations low in the tissues of our bees is to keep populations of mites low in our colonies. Most commercial beekeepers use insecticides to manage the mite populations because the non-chemical methods for controlling mites are more costly and labor intensive.”

To properly combat varroa mites, commercial beekeepers need more varieties of insecticides in their arsenal that are deemed safe for honeybees, Harris said.

“These insecticides need different modes of action, and the beekeepers need to rotate and use different insecticides over time to slow down the development of resistance to any one of the chemicals,” he said.

Hobbyist beekeepers who do not want to introduce insecticides to their hives have possible alternatives that are too labor-intensive and impractical for a commercial beekeeper with thousands of colonies. One non-chemical method, known as drone trapping, involves colonies making drones (male bees) on special combs from March to May.

Once the drones are produced, Harris said, the drone brood is about nine times more attractive than the worker brood in the hive.

“The drone brood attracts the mites like a magnet, and once the drone brood has been capped, beekeepers remove the brood and freeze it to kill the mites inside that brood,” he said. “A single comb of capped drones can have more than 2,000 mites. Done correctly, a hobbyist can trap mites with two rounds of drone combs and remove 90% or more of the mites without ever using a pesticide in the hive.”

High mortality of beehives can reduce the number of colonies available for the managed pollination of crops that need insect pollination. Without enough colonies, the growers risk not getting the maximum number of pollinated blossoms, resulting in a dramatic reduction in crop yield.

While many beekeepers in Mississippi replace dead colonies with new colonies that they can make by budding off new colonies from the strong ones that survived a winter, even the most skilled practitioners have been stretched to their practical limits with high annual losses, Harris said.

“Before the 60-70% loss this winter, our beekeepers saw 35-40% losses annually over the last decade,” he said. “Beekeepers can replace colonies, but it costs them to do so. The profit margins are small, and the effort to replace colonies of bees that die is becoming unsustainable. It is especially tough when cheaper honey from foreign suppliers tends to hold down the price of our domestic honey.”

Access MSU Extension publications on beekeeping online at https://extension.msstate.edu/agriculture/livestock/beekeeping.