Washington, DC–(ENEWSPF)–April 5, 2012. Newly published research has documented that widely used herbicides can adversely impact non-target invertebrate organisms and that endangered species face acute risk from such impacts. Researchers found that adult numbers of the Behr’s metalmark butterfly dropped by one-fourth to more than one-third when its larvae were exposed to herbicides applied in the vicinity of the butterfly’s preferred food source, the naked stem buckwheat plant. The results are especially disturbing because the Behr’s metalmark was being studied as a surrogate for the Lange’s metalmark butterfly, which shares the same habitat and feeding preference and whose population has shrunk from 2,300 in 1999 to less than 100 today. As a federally protected endangered species, the Lange’s metalmark could not be included in the experiment. Researchers concluded that inert ingredients in the herbicide formulations or indirect effects on food plant quality may be causing the increased butterfly mortality.
The research was conducted at the 55 acre Antioch Dunes National Wildlife Refuge in Contra Costa County, CA, which is the only known habitat for the Lange’s metalmark. Refuge managers noticed that the naked stem buckwheat, which is native to the refuge and supports both species of butterflies, was being displaced by invasive plants, including ripgut brome, vetch and yellow starthistle. After suppressive measures, including grazing and mechanical and manual removal of the invasive species proved ineffective, managers resorted to herbicide applications including triclopyr, sethoxydim and imazapyr.
Noticing that the Lange’s metalmark population continued to decline after the herbicide applications began, refuge managers undertook a study of their potential toxicity. Researchers sprayed triclopyr, sethoxydim, and imazapyr at regularly applied rates on Behr’s metalmark larvae and its favorite host plant, naked stem buckwheat. The larvae were then raised in the laboratory over several months, after which time between 24-36% fewer adults emerged from pupation in the herbicide-treated trials compared to controls.
John Stark, PhD, an eco-toxicologist from Washington State University’s Puyallup Research and Extension Center, who co-authored the study said, “A lot of people believe that herbicides don’t have an effect on animal life, but we found that they can have an effect. We found that these three herbicides had a negative effect on these butterflies.” In a small population of endangered animals, Dr. Stark said, “Any kind of reduction like that is going to be a problem.”
The study, funded by the U.S Fish and Wildlife Service (FWS) and published in the journal Environmental Pollution, is one of the first to document the effects of herbicides on butterflies. Several studies have shown herbicides can adversely affect animal life, even though they are designed to kill plants. Since each herbicide in the Behr’s metalmark research has a different mode of action, Dr. Stark speculates that their toxic effects may be due to inert ingredients contained but not identified in the formulations, or indirect effects on food plant quality. Of the three herbicides studied, refuge managers now use only triclopyr, mainly on woody plants and trees in areas far away from prime butterfly habitat.
The area now contained in the refuge is part of a much larger ecosystem that changed significantly when people began digging up the sand dunes to make bricks, many of which were used to rebuild San Francisco after the 1906 earthquake. Nevertheless, in the 1930s, 13 endemic plants and insects were documented living in the dune system, said Louis Terrazas, a FWS wildlife refuge specialist. Mining continued until 1980 when the federal government stepped in to create the refuge amidst the badly fragmented dunes. Of the 13 unique species recorded 50 years earlier, only the endangered Contra Costa wallflower, Antioch Dunes evening-primrose, and the Lange’s metalmark butterfly remain.
Sources: San Francisco Chronicle, beyondpesticides.org
All unattributed positions and opinions in this piece are those of Beyond Pesticides.