Toxicity and safety evaluation of five insecticides on egg parasitoid,Trichogramma evanescens Westwood

Toxicity of five insecticides commonly used in vegetable fields on Trichogramma evanescens Westwood was evaluated under laboratory and glasshouse conditions. All insecticides were applied at concentrations recommended for field application by manufacturers. Toxicity of the insecticides on adult T. evanescens and the parasitoid in four immature stages were tested by exposing the adults to fresh, dry insecticide films in glass vials and by spraying parasitic host eggs respectively. Residual toxicity of the pesticides on female adults of the parasitoid was meanwhile tested at different time intervals by exposing them to potted leaves of Brassica campestris L. sprayed with insecticides. The results show that the insecticides vary in toxicity and have different degrees of effect regarding the survival, emergence, parasitism and longevity of the parasitoid. Bacillus thuringiensis and acetamiorid are non-toxic or low toxic for T. evanescens on all development stages. They have low effect on the longevity and alae development of emerged adults, with relatively short residual period on adult survival and parasitism. With the exception of the treatments in egg and larval stages, abamectin treatment in pre-pupae and pupae stages severely reduces adult emergence and longevity. It also produces higher levels of ateliotic proala compared with the control. Abamectin has strong impact on T. evanescens during developmental stages of the parasitoid. Furthermore, adult survival and parasitism are significantly affected by abamectin 7 days after spray. Lamda-cyhalothrin reduces emergence rate by approximately 92% when applied during pre-mature stages, and enhances mortality of T. evanescens to 70% when applied during adult stage. However, the pesticide has short residual toxicity. Adult survival and parasitism gradually increase to the control level 5 days after spray. Contrarily, chlorpyrifos is highly toxic, both to adult and immature parasitoid. Its residual effect on the parasitoid is still very high after 10 days applied. Overall, Bacillus thuringiensis and acetamiorid are slightly harmful or harmless to the parasitiod and, therefore, there are ideal agents compatible with wasps. On the other hand, abamectin and lamda-cyhalothrin are moderately harmful to the parasitoid. Timing of application of the two insecticides is critical. As chlorpyrifos is harmful to the T. evanescen, its application should be restricted in biocontrol field.