Laboratory Evaluation of the Effect of Insecticides on Non-target Organisms: 2- The egg parasitoid, Trichogramma evanescens West. (Hymenoptera: Trichogrammatidae)

The present study aimed to evaluate the effect of different groups of insecticides (e.g., Dipel, Dursban, Biover, Malathion and Spintor) on the immature stages and the parasitism rate of the egg parasitoid, Trichogramma evanescens West. (Hymenoptera: Trichogrammatidae) under laboratory conditions. The parasitized eggs of the factitious host, the Mediterranean flour moth, Anagasta (Ephestia) kuehniella Zeller were used. Data were recorded in terms of parasitism rate, emergence rate and female percentages. The calculated values of the Slope (b) of the log-dosage-probit mortality curve, by treating the parasitized A. kuehniella eggs (ranged from 0.6 to 1.34), indicated that the susceptibility of the population was heterogeneous for all the studied insecticides. Results indicated that each of the tested insecticides showed the different degree of toxicity. Malathion was the most toxic insecticide (Toxicity ratio T.R.: 10-39.7), while the bioinsecticide, Dipel was the least toxic one (Toxicity ratio T.R.:0.24-0.47). The parasitoid developmental stage had a significant effect on the toxicity ratio of all the studied insecticides. The eggs treated 7-day post-treatment showed the highest parasitism rate for all insecticides, (65-94%), followed by 5-day old (52-91%), 3-day old (48-90%), and then 1-day old (43-88%). An inverse relationship between the parasitism rate and the insecticide concentration was found. The emergence rate was affected greatly by both the type of insecticide and the treated immature stage. The highest emergence rate, (14-86%) was recorded for the eggs treated 1-day post-treatment, while parasitized eggs, treated after 7 days at all the tested insecticides recorded the lowest rates of adult emergence of T. evanescens (6-49%). The highest emergence rate (42-83%) was found for eggs treated with the fungicide Biover, while the lowest values (7-35%) were recorded for the eggs treated with Spintor compared to a significant high emergence rate for the untreated ones (92%). Sex ratio (female percentage) did not differ significantly between the treated (38-55%) and the untreated parasitized eggs (50-54%).