PARENT SESSION
Oral Session # 94: Pathogens, Toxins, and Disease III.
Presiding: C Duffie
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 200.

Historical pesticide use and California amphibian declines.

Davidson, Carlos¹, ¹ Environmental Studies Department, Sacramento, CA, USA

ABSTRACT- Pesticides have long been proposed as a possible cause of amphibian population declines, but due to a number of challenges there has been relatively little research on pesticides and amphibian declines. This study examined the association between the spatial pattern of declines for five California amphibian species and historic pesticide use in California from 1974 to 1991 based on Department of Pesticide Regulation records. Information on declines was derived from maps of historic sites and current population status for the Yosemite toad (Bufo canorus), California red-legged frog (Rana aurora draytonii), foothill yellow-legged frog (R. boylii), Cascades frog (R. cascadae), and the mountain yellow-legged frog (R. muscosa). Generalized additive models were used to analyze the relationship between site status (i.e., presence/absence of each amphibian species) and total upwind pesticide use, upwind pesticide use by 66 pesticide classes, and covariates including spatial location (longitude and latitude), precipitation, elevation, and surrounding urban and agricultural land use. Total upwind pesticide use was a strong, significant predictor of amphibian presence/absence. A model based on total upwind applications of cholinesterase-inhibiting pesticides fit the data significantly better than models based on total pesticides or on any other individual class of pesticides. This is the first study in which population declines of multiple declining species have been associated with historic pesticide applications.

Key words: pesticides, spatial analysis, amphibian decline, California