Effect of insecticides on Trichogramma exiguum (Trichogrammatidae : Hymenoptera) preimaginal development and adult survival

The effect of insecticides on Trichogramma exiguum Pinto & Platner emergenc e, adult survival, and fitness parameters was investigated. Insecticides te sted were lambda cyhalothrin, cypermethrin, thiodicarb, profenophos, spinos ad, methoxyfenozide, and tebufenozide. All insecticides, with the exception of methoxyfenozide and tebufenozide, adversely affected Trichogramma emerg ence from Helicoverpa zea (Boddie) host eggs when exposed at different prei maginal stages of development (larval, prepupal, or pupal). Regardless of t he developmental stage treated, none of the insecticides tested had a signi ficant effect on the sex ratio or frequency of brachyptery of emerged femal es. However, the mean life span of emerged T. exiguum females significantly varied among insecticide treatments, and was significantly affected by the developmental stage of parasitoid when treated. Based on LC50 values, spin osad and prophenofos were the most toxic compounds to female T. exiguum adu lts, followed by lambda cyhalothrin, cypermethrin, and thiodicarb. Insectic ides field-weathered for four to 6 d on cotton leaves showed no activity ag ainst female T. exiguum adults.