ABSTRACT

Acetylcholinesterase (AChE) is the target site of organophosphate and carbamate insecticides and is responsible for the intoxication resulting in death of insects. Partially characterization of AChE and its interaction with organophosphate and carbamate has been studies. The inhibition of AChE by two insecticides; chlorpyrifos and thiodicarb was investigated in the head homogenates of two cotton leafworm Spodoptera littoralis strains; laboratory and field srain; cut worm, Agrotis ipsilon and honey bee Apis millefra. The results obtained revealed that the AChE from different insects is identical in its properties. Highly activity of AChE was detcted in the head homogenate of adult insect of honey bee. The lowest I50 value 10-5 :M (the highest inhibition potency) was obtained with thiodicarb against all the tested insect species. The lowest inhibition was obtained with thiodicarb and chlorpyrifos against field strain of S. littoralis compared to laboratory strain. According to Dixon plots, the inhibition pattern of either chlorpyrifos or thiodicarb was a noncompetitive type.
Key words: AChE, chlorpyrifos, thiodicarb, Spodoptera littoralis, Agrotis ipsilon, Apis
millefra.