Side-effects of insecticides used in tomato fields on the egg parasitoid Trichogramma pretiosum Riley (Hym., Trichogrammatidae), a natural enemy of Tuta absoluta (Meyrick) (Lep., Gelechiidae)

Trichogramma pretiosum Riley is an important natural enemy used for the biological control of Tuta absoluta in tomato fields in several countries in South America. The side-effects of insecticides on T. pretiosum was tested by dipping parasitized host eggs (Ephestia kuchniella Zeller) at three different development stages (egg-larvae, pre-pupae and pupae)in pesticide solution at recommended concentrations. The insecticides varied in their toxicity and significantly affected the development time of the immature stages, emergence, parasitism and longevity of the adult parasitoid. Cartap and phenthoate were harmful and caused total mortality in all the experiments in the three stages of development tested. Lambda-cyhalothrin was not detrimental but caused a significant increase in mortality, prolonged development of the immature stages and decreased the capacity of parasitism of the emerged females. Tebufenozide, teflubenzuron and abamectin had sublethal effects. They reduced the time of development, especially when applied during the pupae stage. The capacity of parasitism of emerged females decreased and was affected by the stage of development treated. With abamectin treatments, parasitism decreased as the development of the parasitoid advanced and the mortality of the emerged adults from host eggs treated during the pupae stage was significantly higher. Tebufenozide reduced parasitism when applied during the egg-larval and pre-pupae stages. The results showed that cartap and phenthoate were harmful, lambda-cyalothrin and abamectin were intermediate, tebufenozide and teflubenzuron were harmless to slightly harmful. Nearly all the chemicals tested had significant sublethal effects.