Persistency and Toxicity of some insecticides on cotton plants to conserve parasitoid wasp,Trichogramma brassicae Bezd.

This study was carried out to investigate persistency of four insecticides (thiodicarb, indoxacarb, proclaim fit and lufenuron) on cotton plants and their toxicity against Trichogramma brassicae .Cotton seeds were sown under greenhouse condition and cotton plants were sprayed with insecticides . Cotton leaves were removed at one-day intervals and were kept in a rearing container with female parasitoids and host eggs. Mortality and sublethal effects of insecticides were recorded every day and their toxicity and persistency were categorized according to the International Organization of Biological Control standard. Results showed that toxicity (with up to 100% mortality) and persistency (>17 days) of thiodicarb was higher than other insecticides and was categorized as a “harmful” and at least a “moderately persistent insecticide. Indoxacarb with up to 52.8% mortality, 62.8% reduction in parasitism and 7 days persistency, was classified as a ”harmful” and “slightly persistent” insecticide. Proclaim fit with up to 37.3% mortality, 47.4% reduction in parasitism and 6 days persistency, was classified as a “moderately harmful” (Group 3) and slightly persistent insecticide. Lufenuron with up to 2.68% mortality, 60.69% reduction in parasitism and 3 days persisitency, was classified as a “slightly harmful” (Group 2) to ”moderately harmful” and short-lived (group 1) insecticide. In conclusion, because of high toxicity and long-term persistency, thiodicarb is not recommended to use in cotton field against cotton bollworm, and a 7, 6 and 3 days “waiting period” was required, respectively between spraying with indoxacarb, proclaim Fit and lufenuron and mass releasing of T. brassicae in cotton fields.