Entomologists at the University of California, Riverside have a "proof of concept" that selenium, a nonmetal chemical element, can disrupt the foraging behavior and survival of honey bees.

Selenium in very low concentrations is necessary for the normal development of insects — and humans — but becomes toxic at only slightly higher concentrations when it replaces sulfur in amino acids. In soils, particularly in Pacific Rim countries and near coal-fired power plants worldwide, it occurs most often in soluble forms, such as selenate.

Wondering what effect selenium concentrations in plants has on honey bees, John T. Trumble, a professor of entomology, and Kristen R. Hladun, his graduate student, performed controlled greenhouse experiments in which they documented the selenium amounts that three plant species — two kinds of mustards and one weedy radish plant — incorporate into their nectar and pollen after the plants had been irrigated with low to moderate levels of the trace mineral.

(For more, see: Accidental bee discovery may prevent CCD)

They then allowed honey bees to visit the plants. They found that the bees fed on food sources, such as flowers that contained selenium at even very high concentrations.

"Nature has not equipped bees to avoid selenium," Trumble said. "Unless the rates of concentrations of selenium were extremely high in our experiments, the bees did not appear to respond to its presence."

Two of the rates of irrigation water Trumble and Hladun tested had selenium concentrations — 0.5 and 0.7 parts per million — that were well below concentrations considered by the US government to be of concern.

"We found, however, that in weedy radish plants even these low rates produced selenium amounts of 60 parts per million in the nectar and 400 to 800 parts per million in the pollen," Hladun said. "But despite these high amounts, the bees would not avoid the selenium."

The researchers also found that bees that had been fed selenate in the lab were less responsive to sugar (as sucrose).

"The selenium interfered with their sucrose response," Hladun explained. "Such bees would be less likely to recruit bees to forage because they wouldn't be stimulated to communicate information about sucrose availability to the sister bees."

Trumble and Hladun also measured the mortality of forager bees that were fed selenium chronically (moderate selenium amounts over a few days). They found that these bees died at a significantly younger age.

Study results appear this month in PLoS ONE.