Toxicity of some insecticides used in maize crop on Trichogramma pretiosum (Hymenoptera, Trichogrammatidae) immature stages

Fall armyworm Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae) is an important pest of maize (Zea mays L.) crops in Brazil. The effects of beta-cypermethrin, chlorfenapyr, chlorpyrifos, spinosad, etofenprox, triflumuron, alpha-cypermethrin/teflubenzuron, and lambda-cyhalothrin/thiamethoxam on Trichogramma pretiosum Riley, 1879 (Hymenoptera: Trichogrammatidae) immature stages were evaluated. Eggs of Anagasta kuehniella (Zeller, 1879) (Lepidoptera: Pyralidae), containing immature stages of the parasitoid were dipped in water solution pesticides, to evaluate their effects on emergence and sex ratio of F-1 parasitoids. For F-2 parasitoids, emergence, parasitism capacity, and sex ratio were evaluated. Beta-cypermethrin, chlorfenapyr, chlorpyrifos, and spinosad affected the emergence success of F-1 T. pretiosum. Insects exposed to etofenprox and alpha-cypermethrin/teflubenzuron during the egg-larval period and to lambda-cyhalothrin/thiamethoxam during the pupal stage also suffered reduction in the emergence. Beta-cypermethrin affected the sex ratio of F-1 T. pretiosum from host eggs treated during the egg-larval period; spinosad affected it during the egg-larval period and the pupal stage, whereas chlorpyrifos did the same when applied during the pupal stage. Chlorpyrifos also affected the sex ratio of F-2 parasitoids, but only when applied during the egg-larval period, whereas chlorfenapyr reduced this trait when applied during the pre-pupal phase. Chlorpyrifos and alpha-cypermethrin/teflubenzuron affected the parasitism capacity of F-1 females from eggs treated during the egg-larval period. Considering the overall effects, only etofenprox and triflumuron were selective on T. pretiosum when applied on parasitized A. kuehniella eggs. Further studies need to be carried out to verify the toxicity of the other pesticides under semi-field and field conditions.