Toxicidade de agrotóxicos utilizados em cultivos de várzea sobre parasitoides de ovos: do laboratório ao campo

Abstract

Crops used in lowland areas, such as rice and soybeans, are affected by biotic factors that cause significant reductions in productive potential, and are currently the main chemical control method used. The erroneous use of this control method can lead to adverse effects on natural enemies, such as Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) and Telenomus podisi (Hymenoptera: Platygastridae), important biological control agents for lepidopterans and pest hemiptera, respectively. Therefore, to assess the compatibility of the use of pesticides and natural enemies, the International Organization for Biological and Integrated Control (IOBC) presents methodologies used globally, involving a sequence of studies in laboratory, semi-field and field conditions. In the laboratory study (manuscript 1), together with the treatments (insecticides registered for the soybean crop) we included a natural stressor (temperature) to assess the possible interactions with the adverse effects caused on T. podisi. Thus, we found that, on adult insects, methoxyfenozide + espinetoram presented an antagonistic interaction as the temperature increased. Unlike chlorfenapyr, where a synergistic effect was observed, with greater effects occurring at 30 ºC. Acephate, spinosad and thiamethoxam + lambda-cyhalothrin caused 100% adult mortality at all temperatures evaluated, however the lethal time was significantly shorter when the temperature increased from 15 to 30 ºC. Chlorantraniliprole had no effect on the parasitoid at the studied temperatures. In the greenhouse (semi-field) bioassays (manuscript 2), we evaluated the deleterious effects on T. podisi of a fungicide, an herbicide and an insecticide widely used in irrigated rice fields and, after determining the rates of dissipation and concentrations for a period of up to 20 days after application, we correlate the results in order to know the respective minimum concentrations so as not to cause significant effects to the parasitoid. From this, our results demonstrated that the estimated half-life times (DT50) were approximately 17, 4 and 5 days for azoxystrobin, cyhalofop-butyl and thiamethoxam, respectively, when applied over rice leaves. For cyhalofop-butyl and thiamethoxam, the extrapolation of the regression line suggests that leaf concentrations below 120 and 6 mg.kg-1, respectively, do not cause significant effects on the life cycle of T. podisi. Finally, in bioassays carried out under field conditions (manuscript 3), we developed a methodology for verifying the reduction of parasitism caused by T. pretiosum, when released inundated and contaminated with insecticides already reported as harmful in laboratory tests. We found that based on our results, the insecticides lambdacyhalothrin, thiamethoxam and zeta cypermethrin were classified according to the IOBC as moderately harmful (Class 3) and, thiamethoxam + lambda-cyhalothrin was classified as harmful (Class 4). Therefore, we conclude that, even causing effects less than those obtained in the laboratory by other authors, these insecticides should not be priorized within a IPM program.