Abstract
The parasitoid Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) is often released to manage lepidopteran pests in cotton crops. However, growers rely on multiple insecticide applications to manage cotton pests. 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), Lepidoptera: Pyralidae] 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 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 (proportion female) 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 decreased the F1 sex ratio (≤ 0.33) compared to the other compounds (sex ratio ≥ 0.45). These results indicate that teflubenzuron is the safest insecticide; the other insecticides are non-selective to T. pretiosum. Field and semifield studies are required to confirm the harmfulness of chlorfenapyr, flupyradifurone and thiodicarb toward T. pretiosum.
Highlights
Cotton is a crop widely cultivated in Brazil, one of the top five cotton-producing countries (Campos et al 2019)
Transgenerational effects occurred on adult emergence, which was reduced on the offspring (F1) of thiodicarb, chlorfenapyr, and flupyradifurone-treated T. pretiosum
Considering that the use of pesticides to control lepidopteran pests in cotton is a limiting factor for the success of the augmentative release of Trichogramma spp., this study aimed to evaluate the lethal and transgenerational effects of insecticides used in cotton on immature T. pretiosum
Summary
Cotton is a crop widely cultivated in Brazil, one of the top five cotton-producing countries (Campos et al 2019). Endemic populations of T. pretiosum parasitizes up to 98% of eggs of the cotton leafworm Alabama argillacea (Hübner) (Lepidoptera: Noctuidae), and parasitism rates increase over the crop cycle (Fernandes et al 1999). Inundative releases of this parasitoid have been reported to yield 76% egg parasitism of Heliothis virescens (Fabricius) (Lepidoptera: Noctuidae) in cotton (Saavedra et al 1997), but establishment of augmented parasitoid populations is halted by spraying of non-selective insecticide (Stinner et al 1974)
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