The sublethal effects of deltamethrin on Trichogramma behaviors during the exploitation of host patches.

Trichogramma and parasitoids as a whole are key species because they regulate natural populations of other insects. As any non-target species, this parasitoid can be exposed to insecticides by environmental pollution. This study identified the effects of an LD 20 of deltamethrin (a pyrethroid) on the behavior of Trichogramma brassicae females infesting a patch of host eggs. The study found that females that survived exposure to the insecticide infested fewer host eggs; spent more time on unsuitable, previously infested host eggs; and infested more previously infested host eggs than controls. The insecticide also induced an increase in antennal and ovipositor rejection of previously infested host eggs. These results are discussed in the light of the mode of action of pyrethroid insecticides. The findings of the study highlight sublethal effects that reduce the fitness of parasitoids and that could consequently modify the equilibrium of natural ecosystems.