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Studies Look at Pesticide Residues in Bats

Date Posted: March 16, 2006

Each year, the Indiana Department of Health Rabies laboratory has approximately 200 to 400 bats submitted for rabies testing. Many of these bats exhibited behavior that brought them to the attention of humans, i.e., they were sick, dying, dead or on the ground. All bats submitted to the rabies laboratory since 1966 have been forwarded to JO Whitaker Jr., at Indiana State University for identification and research purposes. Of the bats submitted from 1966 to 2003, only 5.4 percent of these proved rabid (Whitaker and Douglas in press).

The Service's Bloomington (Indiana) Field Office saw the availibity of these bats as an opportunity to conduct two small studies to determine if Indiana bats might have exposed to organophosphates (OPs), and whether OPs might have contributed to mortality in a some of Indiana bats and northern long-eared bats submitted to the rabies laboratory. In one of the studies, Dr. Whitaker provided nine rabies lab bats to a Service analytical laboratory (Geochemical & Environmental Research Group, Texas A&M laboratory) for chemical analysis. Five Indiana myotis and four northern myotis, all non-rabid, were analyzed.

Analyses included: OPs, organochlorine insecticides, PCBs, and pyrethroids.

In the second study, recent guano samples were collected from priority hibernacula by placing plastic sheets under roosting / hibernating Indiana bats. These sheets were retrieved at various intervals and guano pellets were transferred to clean glass jars and frozen until analysis in 2004. In addition, Service staff also collected for chemical analysis any fresh dead Indiana myotis specimens found during biennial mid-winter hibernacula surveys.

Diazinon was detected in one April mortality Indiana bat, and methyl parathion was found in another. Chlorpyrifos was detected in an August mortality northern long-eared bat. Chlorpyrifos was also detected every Indiana myotis carcass and guano sample from Rays Cave and Wyandotte Cave, important Indiana myotis hibernacula.

Diclorvos was detected in Indiana bat guano from 3 of the 4 caves (Coon, Grotto and Wyandotte) at concentrations ranging from 11  86 ppb, wet weight. No pyrethroid insecticides were detected in any bat carcasses.

Organochlorine pesticides (i.e. DDE, dieldrin, oxychlordane and heptachlor epoxide) are still present in most sample bat carcass samples and PCBs were detected in 8 of 9 bats. Look for a future report addressing these contaminants in bats.

These findings demonstrate organophosphate insecticide exposure is a widespread occurrence with Indiana bats, however we have not identified any cause-effect relationship between these exposures and mortality. It is clear that more investigation is needed on this subject. We are continuing to collaborate with Dr. Whitaker at Indiana State University on this issue and are now focusing our efforts on analyzing rabies lab bats for cholinesterase inhibition in a portion of the brains that the rabies lab is now saving for us.

Chuck Traxler, 612-713-5313

Organophosphate Insecticide Residues in Bats from Indiana (pdf file)

Last updated: June 12, 2015