Development of resistance in the bean aphid, Aphis craccivora Koch., to various synthetic pyrethroids with special reference to change in susceptibility of some important aphid species during the last one and a quarter decade.
The relative toxicity of 7 pyrethroid insecticides was evaluated against adults of Aphis craccivora in the laboratory. On the basis of the LC50s, lambdacyhalothrin, alphamethrin [alpha-cypermethrin], decamethrin [deltamethrin], cypermethrin, fenvalerate and fenpropathrin were 57.08-, 16.00-, 9.997-, 4.35-, 3.81- and 1.72-times more toxic than pyrethrin, resp. A. craccivora was more susceptible than Myzus persicae to all the insecticides tested, whereas, Lipaphis erysimi was more resistant than A. craccivora except to pyrethrin. Deltamethrin was the most toxic to the 3 test species. By comparison with LC50 data for these insecticides from the last 12.5 years, it was concluded that there has been a considerable change in the susceptibility of aphids to synthetic pyrethroids. A 33.9-, 14.8- and 14.5-fold increase in the LC50s was detected for cypermethrin, deltamethrin and fenvalerate, resp. Pyrethrin demonstrated a 14.7 fold increase in LC50, but over 23, not 12.5 years.