Comparative toxicity of selected insecticides to Aphis citricola, Myzus malisuctus (Homoptera: Aphididae), and the predator Harmonia axyridis (Coleoptera: Coccinellidae)

Response of the apple aphid Aphis citricola van der Coot adults to treatment with several classes of insecticides varied from most toxic (esfenvalerate with LC(50) 0.89 ppm [AI]) to least toxic (monocrotophos with LC(50) 385.51 ppm [AI]). Esfenvalerate, which was most toxic to A. citricola, was also most toxic to the aphidophagus coccinellid Harmonia axyridis Pallas. The response of the aphid Myzus malisuctus Matsumura adult to different insecticides varied from highly susceptible (deltamethrin with LC(50) 0.01 ppm [AI]) to highly tolerant (fenpropathrin with LC(50) 6.95 ppm [AI]). Esfenvalerate, which was 3rd in the order of toxicity to M. malisuctus, was the most toxic compound to H. axyridis. Alphamethrin, which showed the lowest selectivity ratio, was also much safer to the predator than to the pest. Based on their selectivity ratios, alphamethrin appeared to be the most promising candidate for use in integrated pest management programs where H. axyridis is the major natural enemy.