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

Abstract

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 decemlineata (Say), were measured in laboratory studies. For both methods of exposure, azinphosmethyl was the least toxic to all life stages tested. The residual toxicity of deltamethrin was at least 4.4-fold higher than either cypermethrin or endosulfan. With the insecticide-susceptible strain, residual toxicities of azinphosmethyl, endosulfan, and deltamethrin were, respectively, 3.5, 5.9, and 4.1 times higher to first instars than to adults and 1.2, 8.1, and 1.6 times higher to third instars than to adults. Contact toxicities of azinphosmethyl, endosulfan, and deltamethrin were, respectively, 3.3, 2.9, and 1.4 times higher to insecticide-susceptible third instars than to adults. In most comparisons, susceptibilities of fourth and third instars were similar. With 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 stage toxicity to current control recommendations for Colorado potato beetle is discussed.