Survival and pesticide exposure of northern bobwhites (Colinus virginianus) and eastern cottontails (sylvilagus floridanus) on agricultural fields treated with counter® 15G

During 1988 and 1989 northern bobwhites (Colinus virginianus) and eastern cottontails (Sylvilagus flondanus) were radiotagged and their daily survival monitored on six study sites treated with the organophosphorus insecticide‐nematicide Counter®15G (terbufos), at the rate of 1.45 kg a.i. per hectare, and on three reference sites. Nonlethal blood samples were collected at the time of capture and during subsequent recaptures to determine exposure to terbufos through blood ChE analysis. Survival rates of radiotagged eastern cottontails and blood plasma ChE activities were not different between treated and reference sites in either year. Gastrointestinal (GI) tracts of two cottontail carcasses found in 1988 contained traces of terbufos in concentrations <0.046 ppm. No terbufos was detected in GI tracts in 1989. There were no differences in survival rates of radiotagged northern bobwhites among treatments. Mean blood plasma ChE activities of northern bobwhites were significantly lower (P < 0.05) on treated sites than on reference sites both years, including sublethal exposure to the test chemical. No GI tract residues were detected in bobwhites in 1988, and GI tract residues were detected in trace amounts (<0.046 ppm) in only one bobwhite carcass in 1989.