Weed killers threaten Lange's metalmark butterfly

Weed killers commonly used to control invasive plants in the Bay Area also kill off butterflies, a federal toxicology study has found.

Butterfly populations common to the Antioch Dunes National Wildlife Refuge dropped by as much as a third when the larvae and host plants were sprayed with each of three standard herbicides, according to the study commissioned by the U.S. Fish and Wildlife Service.

The findings do not bode well for the endangered Lange's metalmark, a once abundant butterfly that now exists only in the Antioch dunes.

"A lot of people believe that herbicides don't have an effect on animal life, but we found that they can have an effect," said John Stark, an eco-toxicologist from Washington State University's Puyallup Research and Extension Center, which co-authored the study. "We found that these three herbicides had a negative effect on these butterflies."

The team of experts was trying to determine whether weed killers harm the Lange's metalmark, but they could not conduct experiments on an endangered species so they used the Behr's metalmark, a close relative.

Stark said the compounds triclopyr, sethoxydim and imazapyr were sprayed on the butterfly larvae and on the insects' favorite host plant, naked stem buckwheat. The larvae were then raised in the laboratory over several months.

All three substances, which are the primary ingredients in common weed killers, had previously been used at the dunes to control invasive weeds.

The results, published this year in the scientific journal Environmental Pollution, showed a 25 percent to 30 percent reduction in the number of adult butterflies that eventually emerged compared to an unsprayed control group.

"When you are dealing with endangered species that are teetering on the brink of extinction, that is a very large number," Stark said.

Read more: http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2012/04/01/BAUU1NR4OH.DTL#ixzz1qyKcCmvu