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Honeybee gene might help fend off varroa mite
 
By DOUG GRAVES
Ohio Correspondent

COLUMBUS, Ohio — Beekeepers who are about to throw in the towel in their fight against the varroa mite may be in for a bit of good news.

Varroa mites are parasites that attack honeybees and infect them with viruses that lead to their deaths. The mites can infest and kill entire bee colonies. But Purdue University researchers such as Greg Hunt, a professor of behavioral genetics, and Jennifer Tsuruda, a post-doctoral researcher, are honing in on genes that help honeybees defend against varroa mites.

This pest is one of the largest factors in bee population declines. Varroa and tracheal mites can decimate hives in one season. The two researchers have searched for genes that provide these defenses and believe they’re closer to understanding how these genes work.

“Bees are fighting back,” Hunt said. “They’re getting rid of the mites themselves. We can select for these traits now, but it’s tedious. If we can identify the genes that influence these traits, we could develop better methods to screen for these genes and speed the process.”

Colony Collapse Disorder is also a chief concern of beekeepers nationwide. Roughly one-third of honeybee hives in the United States are lost to the mites, though no one factor seems to be at blame. Researchers such as Hunt and Tsuruda believe mites and insecticides also are working against the bees, which are important for pollinating food crops and wild plants.

Some bees exhibit a trait called varroa sensitivity hygiene, in which they can somehow sense there are varroa mites sealed into brood cells where honeybee grubs are pupating. The bees uncap the cells and sometimes remove the infested pupae, disrupting the mites’ reproduction process.

“We assume they’re learning the scent of infested pupae and uncapping the cells to see if mites are in there,” Hunt said.
Bees that exhibit the trait were produced and genotyped. Researchers found the inheritance of two chromosomal regions from the resistant parent containing genes that made bees more likely to uncap brook cells and remove infested pupae. The list of candidate genes includes those involved in learning and sense of smell.

“We can start with the genes that make the most sense and run tests to determine if they’re involved in conferring those behaviors,” Tsuruda said.

Other bees being attacked by varroa mites exhibit a grooming behavior in which they swipe at their backs and often remove the mite. In some cases, the bee will bite and possibly kill the mite.
Hunt said maps with approximately 1,300 genetic markers were created to look for the genes responsible for the grooming behavior. The researchers narrowed the research to one region on a chromosome that contains 27 genes.

“The gene Neurexin 1 is a likely candidate,” Hunt said, “because unrelated mouse testing has shown that the gene can be involved in excessive grooming. It raises the possibility that the same gene might be influencing some behavior in two very different species.”
According to Hunt, once these genes are pinpointed, the bees could be specially bred and deployed to address declining honeybee populations.
12/12/2012