Dillapiole Mediated Esterase Inhibition in Insecticide Resistant Spodoptera litura (Fabricius)

Synergism of insecticide toxicity by dillapiole was examined in the third instar laboratory-reared populations of Spodoptera litura collected from Delhi and Guntur. The Guntur population is 10.2, 7.0, 4.8 and 2.3 fold resistant to lambdacyhalothrin, cypermethrin, fenvalarate and profenophos, respectively. Synergistic studies with various insecticides showed that there was significant increase in mortality in both Delhi and Guntur populations. Dillapiole synergized cypermethrin and lambdacyhalothrin against both the Delhi and Guntur population whereas, profenophos synergism with dillapiole was evident only against Guntur population. The combination with fenvalarate was antagonistic to both the population. Esterase inhibition by dillapiole did not occur immediately after dosing, but exhibited maximum inhibition around 3–4 h after dosage in case of Delhi population (susceptible). In Delhi population of S. litura the inhibition of esterase by dillapiole was not instantaneous but reflected only after 2–3 h. On the contrary in Guntur population, the inhibition of esterase occurred over a longer period and this led to an increase in synergistic ratio value of all insecticides. Though there was a reduction in toxicity with less proportion of synergist, increase in the proportion of synergist in the mixture led to an increase in toxicity. The ability of dillapiole in suppression of esterase activity was relatively less compared to that of its dihydro - derivative in terms of the time for which the esterase activity was suppressed.