Adult common green lacewings, Chrysoperla cornea (Stephens) (formerly known as Chrysopa carnea), were collected from alfalfa fields, each separated by approximately 200 to 500 km, in four California counties. Adults, as well as larvae and eggs reared from those adults, were screened with six pesticides: two carbamates (carbaryl and methomyl), two pyrethroids (permethrin and fenvalerate), and two organophosphorus insecticides (diazinon and phosmet), to detect intraspecific variability in their responses to pesticides. Methods for screening adults, larvae, and eggs were developed. Adults and larvae were highly tolerant of field rates of the pyrethroids. Larvae also tolerated phosmet, probably due to hydrolysis by esterase enzymes. Lacewings from the four locations responded significantly differently to all six pesticides. In general, San Joaquin County lacewings exhibited the highest and Imperial County lacewings the lowest mortality, with Kern and Fresno County lacewings variable in their responses. These results correspond with pesticide usage in California. Egg hatch was not affected by any of the pesticides tested. Reciprocal crosses of San Joaquin and Imperial County adults were successful, indicating that reproductive isolation does not exist.