Abstract
Injudicious application of insecticides can cause a sharp reduction in the population of several predatory insects and mites including parasitoids. The current study was designed to investigate the effect of four insecticides (i.e. bifenthrin, cypermethrin, deltamethrin and acetamiprid) against the natural population of hymenopterous parasitoids parasitizing various pests of Alfalfa. When used against the pests of Alfalfa, these insecticides also affected the natural population of hymenopterous parasitoids significantly, resulting into ecological imbalance and making the crop more susceptible to pest infestation. This study has proved that bifenthrin, cypermethrin, deltamethrin and acetamiprid can cause a sharp decline of the population of twelve different hymenopterous parasitoids families of (trichogrammatidae, mymaridae, aphelinidae, encytidae, eulophidae, pteromalidae, eupelmidae, ichneumonidae, braconidae, proctotrupidae, platygastridae and scelionidae) with a detectable variation in their resistance to these insecticides. The comparison of means of survival percentage for different insecticides revealed that cypermenthrin caused the lowest mortality (highest survival percentage) to parasitoids followed by deltamenthrin, acetamiprid and bifenthrin to cause maximum mortality respectively (lowest survival percentage) to hymenopterous parasitoids. This would add further environmental concern to the natural population of several predatory insects as their viability will be significantly affected in different contaminative areas. Thus, such studies are also required to investigate the effects of other insecticides which have been extensively used for pest control.