Periodic checking to detect development of resistance in mustard aphid, Lipaphis erysimi Kalt. to recommended insecticides used for more than two decades

The relative toxicity of emulsions of eleven insecticides was evaluated agalnst the apterous adults of mustard aphid, Lipaphis erysimi Kdt.In the laboratory. On the basis of LC₅₀ values, oxydemeton methyl, chlorpyriphoq dimethoate, methyl parathion and pyrethrum were respectively 25.61,11.92,7.56, 3.79 and 1.37 times more toxic than lindane. The remaining five insecticides, viz, fenitrothion, quinalphos, malathlon, fentbion and endosulfan were respectively 0.98, 0.95, 0.84, 0.65 and 0.58 times less toxic than lindane. A comparison of LC₅₀ values for commonly used and recommended insecticides determined periodically during the last two and a half decades revealed that initially up to 23 years (1969–1991), a pronounced shin in the level of susceptibility of mustard aphid to methyl parathion, dimethoate, malathion, lindane, endosulfan and pyrethrum was recorded. However, amongst the Insecticides tested, initially up to 18 years, methyl parathion, malathion and endosulfan did not show change in toxicity to L. erysimi except lindane where the aphid showed 3.97-fold resistance suggesting sign; of development of resistance. In later years from 1986–1991, the development of resistance in L. erysimi to methyl parathion, lindane ad endosulfan was not rapid except to malathion qhere 6.15-fold resistance was observed. In spite of the phenomenon of increasing LC₅₀ values lodicating existence of resistant straln of Lerysimi, the values of LC₅₀ of recommended insecticides are well within the range of concentrations usually used to control mustard aphid.