Efeito de inseticidas sobre atributos biológicos do parasitoide de ovos Telenomus remus (Nixon, 1937) (Hymenoptera: Platygastridae)

Abstract

The egg parasitoid Telenomus remus (Nixon, 1937) (Hymenoptera: Platygastridae) is considered an important natural mortality agent of Spodoptera frugiperda (Smith, 1797) (Lepidoptera: Noctuidae) because it acts in the insect's egg phase preventing the caterpillars from hatching which will later cause damage. The fall armyworm, S. frugiperda, is one of the main agricultural pests and the main strategy used to control this insect is the application of chemical insecticides. The selectivity of pesticides to natural enemies is an important point within the MIP, where products that control the pest, but do not affect beneficial organisms, should be prioritized. Thus, the aim of this work was to evaluate the effects of acute lethal (mortality) and subletal (parasitismo and emergence rate, sex ratio and longevity) toxicity of the insecticides chlorfenapyr, spinosad and thiamethoxam + lambda-cyhalothrin by tarsal contact on the egg parasitoid T. remus. For acute lethal toxicity bioassays, glass tubes impregnated with 600 μL of the insecticide solution for each treatment were used. Each treatment included five repetitions, each with five pairs of adult parasitoids aged ≤48 h. Mortality was determined 48 hours after exposure. For acute sublethal toxicity bioassays, T. remus females were transferred to glass flasks impregnated with the insecticides' CL50. The experimental design was completely randomized with five replications with 20 females each. Twenty surviving females were transferred to the glass jar containing S. frugiperda egg mass (age <12 h) for parasitism. The parameters evaluated were the rate of parasitized eggs (generation F0), the rate of emergence, sex ratio and longevity of adult parasitoids (generation F1). The results of lethal toxicity demonstrated that thiamethoxam + lambda-cyhalothrin were more toxic to the parasitoid due to the synergistic effect between the two insecticides. In the sublethal toxicity results, all treatments were classified as harmless and did not show significant differences in the rate of parasitism, emergence and sex ratio. The longevity of adults of the F1 generation was shorter in the treatment with thiamethoxam + lambda-cyhalothrin, although there was no significant difference. The risk quotient was lower for spinosad, being classified as slightly to moderately toxic. The rest of the insecticides were classified as toxic. In the demographic growth indices, chlorfenapyr, spinosad and thiamethoxam + lambda-cyhalothrin did not differ significantly. Although none of the insecticides had a significant sublethal effect, they all showed high lethal toxicity, and if necessary, can be used carefully in integrated pest management programs.