Shift in the level of resistance together with relative toxicity of some commonly used and important insecticides to diamond back moth, Plutella xylostella (L.) in Haryana (India)

Larvae of diamond back moth, Plutella xylostella (L.) were collected from cauliflower fields around Panipat, where commonly used insecticides were practically ineffective. This Haryana strain was reared in the laboratory to study the toxicity of eleven insecticides, viz, monocrotophos, endosulfan, fenvalerate, alphamethrin, quinalphos, fluvalinate, decamethrin, malathion, chlorpyriphos, dichlowos and cypermethrin against its third instar larvae. The respective LC₅₀ values (%) were: 1.557, 0.775, 0.766, 0.675, 0.557, 0.505, 0.250, 0.200, 0.143, 0.565 and 0.042, respectively. Cypermethrin was the most toxic i.e., 37.07 times more toxic than monocrotophos followed by dichlorvos against the Haryana strain. This strain in nearly two decades has developed 138.74, 28.47, 6.09 and 5.03-fold resistance to monocrotophos, malathion, endosulfan and dichlorvos, respectively.