Susceptibility of indoor and outdoor whiteflies to certain insecticides and biochemical characterization of their acetylcholinesterase

Five insecticides were evaluated in the laboratory against the adult of two strains of whitefly, Bemisia spp collected from indoor and outdoor grown tomato plants. The toxicity data in terms ofLC50 values showed that Actellic and Agrinate were the most toxic insecticides to indoor strain. Moreover, Decis, Salut and KZ oil showed moderate toxicity. In the meantime, the previous insecticides were close to each other in their toxicity to the outdoor strain The relative toxicity values reflected that ActeHic had 1 01, 1.32, 1.43 and 1.44 fold as toxic as Agrinate, Decis, Salut and KZ oil, respectively against the indoor strain. While, the relative toxicity values revealed that Salut had 1.18, 1.21, 1.22 and 5.34 fold as toxic as Decis, Actellic, Agrinate and KZ oil, respectively, against the outdoor strain. In the meantime, the data showed that the indoor strain was more tolerant to the all tested insecticides compared with the outdoor one. The kinetic studies indicated that outdoor strain had lower Km and Vmax values of AChE compared with indoor strain. The values of Ki were 4.2 and 6.4 M for the AChE of indoor and outdoor strain using methomyl as inhibitor. Moreover, the Linewaver-Burk plots indicated that the type of inhibition of the enzyme from both strains was competitive. These differences among the two strains ofBemisia spp were verified by electrophoretic analysis of proteins. SDSpolyacrylamide gel electrophoresis exibited that the outdoor strain possesses two different bands at 104 KD and —300 KD. However, the indoor strain had a single different band at 250 KD.