Atividade do extrato etanólico de Asclepias curassavica L. no controle de Spodoptera frugiperda (Lepidoptera:Noctuidae) (J.E.Smith,1917) em plantas de milho Zea mays L.

Abstract

Spodoptera frugiperda stands out as the main insect pest in corn. In order to minimize the impacts of chemical pest control, studies of plants with insecticide action are resumed. The present work aimed to verify the action of A. curassavica on S. frugiperda on Zea mays L plants. The plants were collected, dried and ground, and the crude ethanol extract was made from the powder. Tests were carried out in a greenhouse with corn and S. frugiperda of second instar, applied extract at concentrations of 0.5%, 0.25% and 0.1% and flubendiamide, damage, mortality and phytotoxicity were evaluated. Translaminar action test was tested in a greenhouse with second instar caterpillars of S. frugiperda placed in a tissue bag on the corn leaf applied to the abaxial part of the leaf at concentrations of 0.5%, 0.25%, 0, 1% and flubendiamide, damage and mortality were evaluated. Systemic action test was performed with the same parameters, applying extract in the soil at concentrations of 0.5%, 0.25% and 0.1% and flubendiamide. No-choice oviposition preference test was conducted, where couples of pupae were placed in previously sprayed cages with concentrations of 0.5%, 1%, 2% and 4% inside, evaluating egg viability. Three trials were conducted in the field, first extract was applied at concentrations of 1%, 2% and 4% and flubendiamide, the other extracts at concentrations of 0.5%, 0.25% and 0.1% and flubendiamide, evaluating phytotoxicity, damage, plant number, number of leaves and plant height. Ethanol extract was fractionated by liquid-liquid partition with hexane, dichloromethane and ethyl acetate. In the topical application test, the contact action of the crude extract and fractions at 0.5% and 4% was evaluated. The plant extract was phytochemically characterized in order to determine the presence of phenolic compounds, flavonoids and alkaloids. Field conduction test with concentrations of 1%, 2% and 4% reached 100% in the percentage scale of phytotoxicity and it was not possible to proceed with the evaluations. Two years tested with lower concentrations, 0.1%, 0.25% and 0.5%, did not cause phytotoxicity. In both years, the damage caused by S. frugiperda, after 21 days the 0.25% treatment differed from the control. Regarding height, 0.25% and 0.5% stand out in the first year, while in the second year 0.5% shows to be equal to the chemical treatment from the first to the last day of assessment. Despite the different damage, both years the number of plants and leaves did not differ between treatments. In both years, test after 0 hours of application, the treatment containing extract differed from the control, with 0.1% having the highest mortality (75% and 100%). In the test after 48 hours of application, the treatments containing extract did not differ from the control. In both years the food consumption 0 hours, there is a difference in relation to the control in the extract 0.25% treatment. After 48 hours in the first year, treatments containing extract were greater than or equal to the control, unlike the second year. Conversion of feed to weight in both years is observed at 0 hours, all treatments did not differ. However, in the 48-hour trial, treatments containing extract do not differ from each other, but the 0.1% treatment differs from the control. Under greenhouse conditions, ethanol extract at concentrations of 0.25% and 0.5% caused mortality of 50% and 65%, respectively. These same concentrations hold the least damage in treatments containing extract. Phytotoxicity was not found in treatments containing extract. Treatments containing extract did not show systemic and translaminar action. Quantitative phytochemical analysis, the highest polyphenol content is found in ethyl acetate (97.16 µg/ml), flavonoids in the crude extract (1890.27 µg/ml) and alkaloids in hexane (35.80 µg/ml). In the qualitative phytochemical analysis, the crude extract was the only one to present all metabolites (Flavonoids, alkaloids, total polyphenols, triterpenes, cardiotonic glycosides, saponins and coumarins). None of the treatments significantly affected the number of lays, eggs or hatching percentage of caterpillars. Topical application of 0.5% fractions, mortality was not verified in any treatment administered at this concentration, as with 4%, all treatments containing the fractions and the crude extract presented higher mortality data compared to the control treatments being the crude extract the best reaching 75% mortality.