University of Nebraska-Lincoln entomologists continue to help shed light on the global bee crisis.

In the third year of a four-year, $4 million USDA multi-state grant given to 16 U.S. universities, Marion Ellis and Blair Siegfried, entomologists in the Institute of Agriculture and Natural Resources at UNL, and other scientists across the country are studying factors affecting honey bee health that have led to significant losses in the critical insect population.

Ellis said many hoped the group would find a single cause of the losses, but instead, it is more of a cumulative effect of many things.

UNL research specifically is looking at pesticides and effects of certain varroacide and fungicide combinations on honey bee health, Ellis said.

Varroacides are used to kill mites preventing them from destroying bee colonies. Varroa mites first appeared in the U.S. in 1987. Fungicides are used to prevent fungus on orchard crops.

Bees are required to pollinate hundreds of flowering fruit, vegetable, seed and nut crops. Without bees, these crops are unable to produce.

So far, research at UNL has indicated some varroacides are significantly more toxic to honey bees when applied together.

Similarly, varroacides, also can become more toxic to bees when they are exposed to some a fungicides used on orchard crops.

"This suggests that beekeepers should avoid applying these varroacides when honey bees are placed in orchards or other crop settings where exposure to sterol biosynthesis inhibiting fungicides is likely," he said.

Normally varroacides and fungicides are well-tolerated by honey bees, but pre-exposure to a sterol biosynthesis inhibiting fungicide like prochloraz increased the honey bee toxicity of fluvalinate, a varroacide used by beekeepers, by a ratio of nearly 2,000 times in the most extreme case.

Coumaphos and fenproximate – two other miticides used by beekeepers – exhibited a lower, but significant, increase in toxicity to honey bees pre-exposed to prochloraz.

This summer, colony level experiments will be conducted to assess the effects of exposure to simultaneously applied field-relevant doses of miticides and fungicides on brood survival, weight gain and queen performance.