Pinhead-sized varroa mites feed on bees, weakening them.
Pinhead-sized varroa mites feed on bees, weakening them.

Purdue University researchers say they believe they're zeroing in on genes that help honeybees defend against varroa mites, one of a handful of pests that weaken the winged pollinators.

Greg Hunt, a professor of behavioral genetics, and post-doctoral researcher Jennifer Tsuruda are studying certain honeybees that have developed defensive behaviors that allow them to kill or disrupt the mites, according to a news release.

The West Lafayette, Ind.-based scientists are searching for the genes that allow the bees to fight the parasites.

"We can select for these traits now, but it's tedious," Hunt said in the release. "If we can identify the genes that influence these traits, we could develop better methods to screen for these genes and speed the process."

Some bees exhibit what is called varroa sensitivity hygiene.

Somehow they sense that varroa mites are sealed in brood cells, where bee larvae are pupating.

The worker bees uncap the cells and remove the infested pupa, disrupting the mites' reproductive process.

Other bees use a grooming behavior in which they swipe at their backs to remove the mite.

The researchers genotype bees that exhibit these behaviors to try to identify the responsible genes.

For the past several years, honeybee producers have reported about one-third of their colonies due off during the winter.

So far, researchers have not pinpointed the cause of colony collapse disorder.

But many believe a number of factors, including varroa mites, are to blame.