Side effects of insecticides applied to cotton on adult Trichogramma pretiosum by three exposure routes

Abstract

BACKGROUND:Trichogramma pretiosumRiley (Hymenoptera: Trichogrammatidae) is released in extensive areas cultivatedwith cotton worldwide, but the use of synthetic insecticides threatens the establishment of augmented populations. Thus,an assessment of insecticides’effects onT. pretiosumis required to establish their compatibility with mass releases of the par-asitoid. We studied in the laboratory the impact of insecticides administered through different exposure routes (direct-spray-ing, ingestion and residue contact) onT. pretiosum. Based on their toxicity, the insecticides were rated into four categories(harmless, slightly harmful, moderately harmful and harmful) as per the International Organization for Biological Control.RESULTS: The survival, parasitism ability and emergence of the treated adults and offspring (F1and F2), in addition to the per-sistence of the toxic effects in semi-field conditions, were assessed. Teflubenzuron did not reduce female survival and caused alesser impact onT. pretiosumon both direct-spraying and ingestion bioassays. In the residue contact bioassay, teflubenzuronandflupyradifurone were rated as harmless and slightly harmful, respectively. The other active substances (chlorfenapyr, thio-dicarb and methomyl) were harmful to the parasitoid by all exposure routes and were persistent (with toxicity duration surpass-ing 30 days).CONCLUSION: From thesefindings, teflubenzuron is the insecticide most compatible withT. pretiosumreleases and should bepreferred over the other active substances. Further studies with the harmful insecticides (thiodicarb, chlorfenapyr and metho-myl) are required to determine their toxicity underfield conditions and confirm their incompatibility withT. pretiosumreleases.