17
Jul
Same Pesticides that Are Killing Bees Killed Off Dozens of Goldfinches in Modesto, CA, Study Finds
(Beyond Pesticides, July 17, 2019) A March 2017 bird kill incident in Modesto, CA can be traced directly back to an insecticide “soil drench” applied to the base of several elm trees by pesticide applicators hired by the city, as detailed in a study published last month in the Journal of Environmental Toxicology and Chemistry. The chemical in question, the neonicotinoid imidacloprid, is implicated in the ongoing pollinator crisis and insect apocalypse, but can also affect bird populations. Prior research estimated that a single seed coated with the insecticide is enough to kill a songbird; this study confirms that such a scenario can and does play out in the real world. Progress and improvement will only occur when pest management practices stop focusing on pesticide use to solve routine pest problems and emphasize prevention.
As part of city-wide pest management activities, Modesto officials said that imidacloprid was applied to elm trees in several front yards in a local neighborhood. The application took the form of a “soil drench,” which is when pesticide products are applied to the soil around the base of a tree or shrub. The systemic property of imidacloprid and other systemic insecticides means that the chemical will move through the soil, be taken up by the roots and translocated into the rest of the the plant.
While that mechanism poses significant risks to bees and a range of insect pollinators that feed on pollen, nectar, and dew drops contaminated by the systemic insecticide, it is the drench itself that led to the death of over two dozen goldfinches in Modesto. Researchers determined that elm seeds that had fallen from the tree prior to the application were contaminated with imidacloprid during the soil drench. Goldfinches that ate the seeds experienced acute poisoning and sudden death, some falling from their perch to crashing to the ground after attempting to fly.
“The mortality event investigated in the present study highlights a previously unidentified risk of drench application for imidacloprid,” said study co-author Krysta Rogers, Wildlife Investigation Laboratory Investigator, in a news release. “The pesticide label states that the product be applied to the base of the tree and directly to the root zone. [However] Seeds, insects, or other invertebrates consumed by birds and other animals may be present within that zone. If these food items were contaminated during the drench application, they would be highly toxic to animals when ingested.”
Researchers autopsied the birds, finding elm seeds and detectable levels of imidacloprid in the gizzard contents (between 2.2-8.5 ppm) and liver tissue (between 2.1-4.8 ppm) of the affected goldfinches, consistent with the presence of imidacloprid on elm seeds found around soil drenched trees.
The City of Modesto indicates that applicators followed the label correctly. Consequently, this incident points to a serious, but not unexpected, shortfall in the U.S. Environmental Protection Agency’s (EPA) regulation of toxic pesticides. EPA aims to avert risks from inherently hazardous substances through the proper application of these hazardous substances. However, as Beyond Pesticides has long pointed out, regulating pesticides primarily through label statements is inherently flawed, given the complexity of real world scenarios that can occur and result in harm to wildlife and human health.
Researchers intimate that it is possible that such poisonings may be widespread, but “may not be on the list of differential diagnoses unless it is known that a pesticide application took place.” While it is typical to find birds with seeds in their digestive tracks, researchers would not consider testing them for poisoning without prior knowledge of pesticide use in an area.
The study concludes by urging pest managers to look towards integrated approaches that discourage “the prophylactic use of pesticides” that resulted in the death of the goldfinches in Modesto. Pesticide use should never be the first tool land managers use in their toolbox. All other options, including cultural, mechanical, biological, and habitat manipulation, should be attempted before considering even less toxic pesticidal products. For more information on healthy tree care, see Beyond Pesticides’ “Mail” section from its spring 2018 newsletter, and for issues with tree pests, see the ManageSafe webpage.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source: UPI, Journal of Environmental Toxicology and Chemistry
