“Mighty” mites threaten to bring honey bees to their knees

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Varroa mites are deadly for Michigan's fruit and vegetable crops. (view larger image)

Varroa mites are devastating pests that are a serious threat to honey bees and agriculture worldwide, including Michigan’s fruit and vegetable crops that depend on honey bee pollination.

Two Michigan State University (MSU) AgBioResearch entomologists are studying how varroa mites, which deform or kill young bees, develop resistance to a class of pesticides called pyrethroids that are commonly used to control them. Varroa mites can kill honey bee colonies within one to two years, if left untreated.

Professor Ke Dong and associate professor Zachary Huang are working on long-term solutions that will benefit beekeepers and growers in Michigan and around the world. 

“To effectively manage pyrethroid resistance in varroa mite populations, we need to understand why varroa mites are resistant to pyrethroids,” Dong said.  “Once we identify resistance mechanisms, we can develop methods for early detection of resistance in mite populations and possibly find alternative ways to control resistant mites.”

Pyrethroid resistance is a serious global problem. Many insect pest species have developed resistance to pyrethroids.  One major mechanism of pyrethroid resistance is manifested in reduced sensitivity of the insect nervous system to pyrethroids due to mutations in sodium channels.  

Dong is an insect toxicologist in the MSU Department of Entomology. Her lab is internationally renowned for studying sodium channels, which are essential for the initiation and propagation of the action potential in almost all excitable cells (cells that are able to produce and respond to electrical signals). They are the primary targets of several important classes of insecticides, including pyrethroid insecticides.

Sodium channels are gates on cell membranes that allow sodium ions to move into cells when cells are excited. Sodium channels must then close quickly to allow the cells to be prepared for the next nerve impulse.

Pyrethroid insecticides bind to sodium channels so that they do not close properly, and insects, like the mites, die from overstimulation. Most insects have specific mutations that confer resistance to pyrethroid. The results of the studies show that none of the previously known pyrethroid resistance-associated insect sodium channel mutations were found in pyrethroid-resistant varroa mite. Instead four novel mutations were found in pyrethroid resistant mite populations in Michigan and Florida.

“We have successfully expressed a mite sodium channel in an in vitro system which has allowed us to study how pyrethroids act on the mite sodium channel and why pyrethroids are not effective on modifying pyrethroid-resistant mite sodium channels,” Dong explained.  “This fundamental knowledge will be valuable in identifying new insecticides that may be effective on resistant mite sodium channels.”

Huang, also in the MSU Department of Entomology, is a specialist in apiculture (beekeeping)—his research focuses on anything related to honey bees. He is investigating which genes are involved in mite reproduction to provide additional information to solve the problem.
“This mite is perhaps the worst enemy for honey bees worldwide,” Huang said. “It is a big problem for agriculture because nearly 80 percent of food crops depend on pollination.”

Meanwhile, Huang has invented a device for varroa mite control and a patent has been granted on the device—the MiteZapper. This unit combines mite biology with simple physics to treat varroa mite infestations. It has proven 85 percent to 95 percent effective in controlling the mites, without the use of chemicals. Mitezapper L.L.C. is marketing the device. Price and other information is available at http://mitezapper.com.

In addition to support from AgBioResearch, the varroa mite project has received funding from Project GREEEN (Generating Research and Extension to meet Economic and Environmental Needs), the state’s plant agriculture initiative at MSU, and the U.S. Department of Agriculture National Research Initiative.

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