Side-Effect of Certain Herbicides on Egg Parasitoid Trichogramma evanescens (West.) (Hymenoptera: Trichogrammatidae)

Three laboratory experiments were conducted to evaluate the side-effects of four common herbicides used to control weeds associated with local crops on egg of the parasitoid Trichogramma evanescens. These herbicides are Glyphosate 48%SL, Bromoxynil 24%EC, Thiobencarb 50% and Clodinafop-propargyl 15%WP. The biological aspects such% parasitism, % adult emergence, sex ratio, developmental period and % mortality of the developmental T. evanescens stages were studied. The first experiment tested the effect of herbicides on the biological aspects of T. evanescens. Sitotroga cerealella fresh eggs exposed to low concentrations of glyphosate had a high parasitism viability (85.5%) and higher percentage of T. evanescens adult emergence (91.14%), that was closely similar to the untreated 89.88% and 95.59%, respectively. Negative relationship was observed between herbicidal concentration and both of parasitism and adult emergence in all tested herbicides. Herbicides regardless to concentrations had different adverse effect on T. evanescens percent of parasitism being classified gradually from moderately harmful to harmless as following; thiobencarb (9.83%), bromoxynil (29.46%), clodinafop-propargyl (42.83%) and glyphosate (69.23%), respectively compared to high percentage of parasitism (89.88%) in the untreated. The second experiment determined the impact of herbicides on immature stages of T. evanescens. Parasitized eggs treated after 8 days (one day before emergence) with all tested herbicides recorded a significant low rate of adult emergence of T. evanescens compared to those treated 3 and 5 days after parasitism. The third experiment free-choice and non-choice trails were conducted to evaluate the acceptance of the female wasps to the less toxic herbicides. The effects of the tested herbicides were varied in both free-choice and non-choice tests, thiobencarb showed a significant strong impact (on the tested parasitoid with low parasitism and no emergence of T. evanescens wasps. While the negative effect of glyphosate on the tested parasitoid was weak with a significant high percentage of parasitism and adult emergence compared to the untreated. Results reflected that the tested herbicides classified gradually from moderately harmful to harmless as following; thiobencarb, bromoxynil, clodinafop-propargyl and glyphosate. Among the tested herbicides, the harmless ones should be chosen in a program of integrated pest management (IPM) since it allows the use of pesticides without harm to the biological control agent T. evanescens. On the other hand, the moderately harmful pesticides should be excluded or replaced by another product with less impact whenever it is possible.