Lethal, Sublethal And Transgenerational Effects of Insecticides Labeled For Cotton On Immature Trichogramma Pretiosum

Abstract

The egg parasitoid Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) regulates lepidopteran pest populations in cotton crops. However, cotton harbors dozens of pests, and growers rely on multiple insecticide applications to manage these damaging organisms. A harmonious integration of control tactics is required for proper pest management, and the use of selective insecticides (i.e., those promoting effective pest control while causing little impact on natural enemies) fits within this scope. This study aimed to assess the lethal, sublethal and transgenerational effects of insecticides from varying chemical groups on T. pretiosum. The insecticides were sprayed on parasitized host [Ephestia kuehniella (Zeller)] eggs with developing T. pretiosum stages (egg-larva, prepupa and pupa), and biological traits were assessed following adult emergence. Overall, pupae were more susceptible to the insecticides. We found thiodicarb and chlorfenapyr to reduce F0 adult emergence in rates comparable to the positive control (methomyl). Adult F0 deformation was the highest on flupyradifurone-treated organisms, and both the F0 parasitism rate and female survival were reduced by the insecticides (except for teflubenzuron). The sex ratio was affected by thiodicarb and flupyradifurone. Transgenerational effects occurred on adult emergence, which was reduced on the offspring (F1) of thiodicarb-, chlorfenapyr-, and flupyradifurone-treated T. pretiosum. In addition, thiodicarb lessened the F1 sex ratio. Combined, these results indicate that teflubenzuron is the safest insecticide; the other insecticides (especially thiodicarb and chlorfenapyr) are non-selective to T. pretiosum. Field and semifield studies are required to confirm the harmfulness of thiodicarb and chlorfenapyr towards T. pretiosum.