Toxicidade de extratos de Strychnos pseudoquina (LOGANIACEAE) para Spodoptera frugiperda (LEPIDOPTERA: NOCTUIDAE)

Abstract

The fall armyworm (Spodoptera frugiperda) is a polyphagous pest that causes economic damage to important agricultural crops. Not unlike most insect pests, their control is carried out almost exclusively with organosynthetic insecticides, which makes this situation questionable in terms of their agronomic efficiency and also in terms of safety for humans and the environment as a whole. The use of plants to control insect pests goes back many years, however, in Brazil, particularly in the Cerrado region, little is known about the flora with potential use for controlling insect pests. Therefore, this work aimed to investigate the toxicity of leaf and stem bark extracts, as well as secondary metabolites isolated from the bark of Strychnos pseudoquina, on a population of S. frugiperda, under laboratory conditions. Extracts of bark and leaves of this plant were fractionated using different solvents (ethyl acetate, ethanol, methanol and hexane) and the flavonoids 3-O-methylquercetin and strychnobiflavone were refracted from the ethyl acetate extract of the bark. The fractionated extracts with the different solvents, and also the two flavonoids, in different concentrations, were offered together with food for the neonate larvaes. The isolated flavonoids were also topically applied to the neonate larvaes. Antixenosis and antibiosis effects of extracts from the bark and leaves of the plant and isolated secondary metabolites, offered to neonate larvaes were evaluated. Our results highlighted the larvicidal effect promoted by all fractions of the investigated bark extract. Regarding the leaf extract, only the extract obtained from the ethyl acetate solvent showed larvicidal effect. The two flavonoids tested did not show a significant larvicidal effect, however, the possibility of promoting some deleterious effect on the insect when in synergism with other secondary metabolites of the plant cannot be ignored. Other biological variables verified in the population of S. frugiperda treated with plant extracts were: repellency of newborn larvaes, food consumption of treated leaves, larval and pupal weight, changes in the duration of the life cycle, reason sex and some abnormalities visible in insects throughout the study are presented in the work. Outstanding larvicidal effect of all extracts of the bark and the extract of leaves obtained from the solvent ethyl acetate indicate the potential of this plant to be used in management programs for this pest.