Relative Toxicity of Some Synthetic Insecticides with Special Reference to Change in Susceptibility Level of Myzus Persicae Sulz Over A Decade

The toxicity of various synthetic pyrethroids and organophosphorus insecticides to green peach aphid, Myzus persicae Sulz has been worked out by direct spray and leaf dip method in the laboratory. Amongst the synthetic pyrethroids evaluated alphamethrin was found to be most toxic insecticide, the relative toxicity values being 10.08 and 6.96 times higher than that of cypermethrin by direct spray and leaf dip method, respectively. Profenophos was the most toxic organophosphorus insecticide followed by chlorpyriphos, methyl demeton, triazophos and quinalphos. Out of the two methods of bioassay, leaf dip method was found to be the most effective. A comparison of LC₅₀ values for commonly used and recommended insecticides determined over a decade revealed that there has been a shift in susceptibility to various insecticides used where aphid showed 64.3, 52.7, 51.9 and 6.0 fold resistance to γ-cyhalothrin, deltamethrin, fenvalerate and cypermethrin, respectively. However, there was only 2.5 and 1.4 fold increase in the LC values of methyl demeton and alphamethrin during the same period.