Effect Of Sublethal Insecticide On Natural Enemies And Acetylcholinesterase Assay

1. The host insects were treated with sublethal dosages of mothamidophos in Plutella xylostella (Lepidoptera: Yponomeutidae) and of methamidophos and avermectin in Lipaphis erysimi Kaltenbach (Homoptera: Aphididae). The concoon formation in the two parasitoids, Cotesia plutellae (Hymcnoptcra: Braconidac) and Diaeretiella rapae (M'Intosh) (Hymcnoptcra: Aphidiidae), decreased significantly, from 17.6% and 16.5% (control) to 8.43% and 8.57% (with methamidophos treatment), respectively. The adult emergency in C. plutellae and D. rapae in control (93.5% and 99.4%, respectively) was significantly lower than those in treatment with methamidophos (86.0% and 92.5%, respectively). In addition, when parasitized L. erysimi were treated with sublethal dosages of methamidophos, spinosads, and avermectin, the cocoon formation decreased significantly.2. The acetylcholinesterase (AChE) sensitivity to methamidophos and dichlorvos in the resultant emerging adults of the two parasitoids was found to be significantly lower than in the control.3. The acetylcholinesterase (AChE) sensitivity to methanmidophos and dichlorvos in the adults of the two parasitoid species and ladybird Propylaea japonica (Thunberg) were substantially higher than those in the adults of three herbiborous pest insects, P. xylostella, L. erysimi and Bemissia tabaci (Gennadius) (Homoptera: Aleyrodidae). The order of AChE sensitivity to methamidophos and dichlorvos was the two parasitoid wasps > predator P.japonica > the three herbivorous pest insects.It is suggested that there is a difference in AChE sensitivity to insecticides between the resultant emerging parasitoids with and insecticide pre-treatment. Furthermore, the introduction of the insecticides to the host insects could be an important factor in the endoparasitoids' insecticide resistance development. There exists a different potential for the development of resistance to insecticides among herbivorous pest insects and insects and their predators and their predators and parasitoids. Possible association of the insects' insecticide susceptibilities to their field conditions and the differences in the insects' biological response to the environment among, predators and parasitoids are discussed.