Avaliação da toxicidade e de efeitos subletais da combinação de inseticidas sintéticos e botânicos em Spodoptera frugiperda

Abstract

The fall armyworm Spodoptera frugiperda, known for the damage it causes to plant production and for its high migratory capacity, is present in more than 80 countries. This insect stands out for its polyphagy, high fecundity and short life cycle, causing serious damage to several crops, especially corn. Control of this pest has been made difficult due to its developed resistance to different groups of insecticides and genetic modification technologies. Therefore, this study aimed to evaluate whether the combination of conventional insecticides with botanical compounds presents lethal effects capable of reversing the resistance of S. frugiperda, making it susceptible to organosynthetics again. Furthermore, the ability of these mixtures to cause sublethal effects was investigated, with findings indicating a negative impact on the sense of smell of adults and the leaf consumption of the caterpillar. The experiments included susceptibility tests in a Potter tower, using field doses of the insecticides Premio® (chlorantraniliprole), Decis® (deltamethrin) and Lannate® (methomyl). Mortality and survival curves were then established using these insecticides and the essential oil (EO) of Lippia sidoides and thymol, its major compound. For all compounds, combinations of the lower and upper limits of the confidence intervals of the lethal dose to kill 50% of the population (LD50) were analyzed to identify possible synergistic, antagonistic or additive effects. In sublethal bioassays, the influence of isolated and mixed compounds on the sense of smell of males and females was evaluated, as well as on the food preference and consumption of third-instar larvae. The results confirmed the resistance of S. frugiperda to the insecticides chlorantraniliprole and deltamethrin, both of which presented mortality rates below 80%. Among the synthetics, deltamethrin was the most toxic, with LD50 = 0.00839 μg/mg, and the most efficient in reducing larval survival time. Among the botanicals, the essential oil of L. sidoides showed greater toxicity, with LD50 = 2.690 μg/mg. The combination of treatments revealed synergism between the synthetic insecticides and the essential oil of L. sidoides, and additivity in the mixture of synthetics with thymol. In sublethal effects, it was found that the mixture of organosynthetics with the essential oil altered the adults' sense of smell and the larvae's feeding. These results confirm the promising potential of the combination of chlorantraniliprole and deltamentrin with L. sidoides EO and thymol in the control of S. frugiperda, also demonstrating its ability to induce sublethal effects in this insect.