TOXICITY OF SELECTED INSECTICIDES TO SEVERAL LIFE STAGES OF COLORADO POTATO BEETLE, LEPTINOTARSA-DECEMLINEATA (SAY)

Residual and contact toxicities of several insecticides to larvae and adults of insecticide-susceptible (four insecticides) and insecticide- resistant (three insecticides) Colorado potato beetle, Leptinotarsa de cemlineata (Say), were measured in laboratory studies. For both method s of exposure, azinphosmethyl was the least toxic to all life stages t ested. The residual toxicity of deltamethrin was at least 4.4-fold hig her than either cypermethrin or endosulfan. With the insecticide-susce ptible strain, residual toxicities of azinphosmethyl, endosulfan, and deltamethrin were, respectively, 3.5, 5.9, and 4.1 times higher to fir st instars than to adults and 1.2, 8.1, and 1.6 times higher to third instars than to adults. Contact toxicities of azinphosmethyl, endosulf an, and deltamethrin were, respectively, 3.3, 2.9, and 1.4 times highe r to insecticide-susceptible third instars than to adults. In most com parisons, susceptibilities of fourth and third instars were similar. W ith the insecticide-resistant strain, azinphosmethyl, endosulfan, and deltamethrin were, respectively, 3.2, 1.6, and 8.0 times more toxic to third instars than to adults. The importance of differential life sta ge toxicity to current control recommendations for Colorado potato bee tle is discussed.