O extrato hexânico de Ricinus communis é toxico a Spodoptera eridania (Lepidoptera: Noctuidae)?

Abstract

The leafy caterpillar, Spodoptera eridania (Cramer, 1782) (Lepidoptera: Noctuidae) is a polyphagous insect that is difficult to control, due to its behavior and voracity. An alternative that has been used is the botanical insecticides, which have potential for insect control, varying according to the plant species, extracting solvent and the target species. In this sense, the present work aimed to evaluate the lethal and sublethal effects of the hexane extract of castor bean, Ricinus communis, on S. eridania, under laboratory conditions. The hexane extract was acquired through the LABCON stock, evaluated at diferente concentrations (1%, 2% and 4%) in two application strategies (food and contact). As a negative control, sterile distilled water was used and as a positive control, the synthetic commercial product (Thiamethoxam + Lambda­cyhalothrin), as recommended in the package insert. The design used was completely randomized, containing 10 treatments and six replications, with 12 insects each, totaling 72 insects per treatment. After the applications, the plates were identified and stored in climatized chambers, at a temperature of 25 ± 2°C, RH of 70 ± 10% and a photophase of 14 hours. The evaluations were carried out every 24 hours, quantifying the number of dead caterpillars during 10 days. After this period, the development of surviving larvae was monitored, evaluating pupae weight, percentage of pupation, duration of the pupal phase, sex ratio and emergence. It was verified that the effect of the hexane extract of R. communis on S. eridania varied according to the concentration and application strategy, however, the concentrations of 2% and 4% were more effective regardless of the medium in which they were inserted. In addition, both concentrations caused sublethal effects such as reduction in pupa weight, change in sex ratio and percentage of pupation, which may compromise the next generation.