Side effects of certain common insecticides used in cotton fields on the egg parasitoid, Trichogramma evanescens west. (Trichogrammatidae: hymenoptera)

Abstract

Studies on the toxicity of some common insecticides used in cotton fields against Trichogramma evanescens were carried out under laboratory and field conditions following the guidelines recommended by International Organization for Biological Control (IOBC). Field Recommended Concentrations (FRCs) of five insecticides viz., Dursban 48 %, Sumi-alpha 5 %, Cascade 10 % Spinotor 24 % and Agerin were tested against immature stages of the egg parasitoid under laboratory conditions. Concerning the insecticide effects on the development of immature stages inside host eggs, results revealed only Sumi-alpha, Dursban and Spintor were categorized as "class 3-moderately harmful (80 ≤ E ≤ 99%), while, Agerin and Cascade 10 % were categorized as class 1-harmless (E < 30%) to all. In the experiment free-choice and non-choice trails were conducted to evaluate the acceptance of the female wasps to the less toxic insecticides. It is evident from the results presented with free-choice and non-choices of treated eggs females of T. evanescens significantly reduced the parasitism and adult emergences of eggs treated with Dursban, Sumi-alpha, and Spintor, while, in the case of Agerin and Cascade 10 % were considerably safe. Under field conditions, after spraying directly, despite the statistically significant differences among the treatments, only Sumi-alpha and Dursban were categorized as "class 3-moderately harmful (80 ≤ E ≤ 99%). While, Cascade 10 % was categorized as class 2-slightly harmful (30 ≤ E ≤ 79%), Agerin was categorized as class 1-harmless (E < 30%), according to the IOBC ranking. After five days from spraying, Spintor was the most effective treatments followed by Dursban and Sumi-alpha on reducing the percentages of parasitism of the egg parasitoids of T. evanescens. Only Spintor and Dursban were categorized as "class 2 = slightly harmful (30 ≤ E ≤79 %), while, Agerin , Cascade and sumi-alpha were categorized as class 1-harmless (E < 30%), according to the IOBC ranking Among the tested insecticides, 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.