Discoveries by MSU Scientists May Lead to New Ways to Control Honeybee Parasite

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Ke Dong (view larger image)

A series of groundbreaking discoveries by Michigan State University entomology researchers—two of them MAES researchers—about sodium channels in the Varroa mite, a parasite of honeybees, may help other scientists develop compounds that keep bees safe from the deadly pest.

Sodium channels are proteins in cell membranes that conduct sodium ions through the membranes. The MSU scientists have induced frog eggs to produce sodium channels from Varroa mite nerve cell membranes in the lab, the first time this has ever been done. Because previous attempts by other scientists to produce this type of non-insect sodium channel in the lab had failed, it was thought that some other cell component was needed for expression. But the MSU team found this wasn’t the case.

The researchers also discovered that the Varroa mite sodium channel reacts to chemicals differently than the honeybee sodium channel. This is the first time that this has been documented.

The research is published in the Dec. 4 issue of The Journal of Biological Chemistry.

“The sodium channel is the cellular target of the pyrethroid insecticide fluvalinate, which is used to control Varroa mites,” said Ke Dong, MAES entomologist. “But we have problems with mites developing resistance to fluvalinate because of mutations in the mite sodium channel. Successful expression of the mite sodium channel in vitro in the lab now allows other scientists to do pharmacological research and find new compounds that target the mite channel but don’t affect the honeybee sodium channel.”

Fluvalinate disrupts the sodium channels in mite nerve cell membranes, paralyzing the mite and eventually killing it. But pesticides can potentially harm the bees, too, and also may contaminate the honey if not used extremely carefully.

The MSU scientists also found the two amino acids that make the mite sodium channel resistant to tetrodotoxin (TTX), a deadly poison found in pufferfish. This resistance mechanism is the same in jellyfish and flatworms. TTX also targets sodium channels, so understanding the mechanism of the Varroa mite’s resistance to TTX will help scientists as they create new compounds to control the mites.

Other members of the MSU team are Yuzhe Du, senior research associate; Yoshiko Nomura, visiting scholar; Zhiqi Liu, former research associate; and Zachary Huang, MAES researcher, all in the Department of Entomology.

Varroa mites invaded the United States from the eastern hemisphere in 1987 and can kill an entire honeybee colony within a year. The mites wiped out nearly 50 percent of the U.S. commercial honeybee population in 2004.

“These mites are a big, big problem for agriculture,” Huang said. “Nearly 80 percent of food crops depend on pollination.”

In Michigan, fruit and vegetable crops valued at $400 million depend on honeybee pollination, and honey and beeswax add another $5 million to the state’s economy each year.

This research is funded by the U.S Department of Agriculture and Project GREEEN, Michigan’s plant agriculture initiative at MSU. The research of Dong and Huang also is supported by the Michigan Agricultural Experiment Station.

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