Quais os efeitos da fração hexânica do extrato de frutos e sementes de mamona sobre Anticarsia gemmatalis Hubner, 1818 (Lepidoptera: Erebidae)?

Abstract

The use of plants as insecticides is something ancient for humans. However, with the advent of new technologies and synthetic chemical insecticides, this use has been given a new meaning. Currently, there is an increasing search, at a national and global level, to use botanical insecticides as an alternative to synthetic chemical insecticides, as observed in Brazil, with the government creating programs that encourage the development of bio-inputs for more sustainable agriculture. Among the plants with insecticidal potential, castor bean, Ricinus communis L (Euphorbiaceae), which has several uses in industry, is cultivated in different regions of the country and has already demonstrated an insecticidal effect on several pest insects. In this sense, the objective of this work is to evaluate the lethal and sublethal effects of the hexane fraction of the extract of fruits and seeds of R. communis (FHFSRC) on eggs and caterpillars of Anticarsia gemmatalis. To this end, 3 bioassays were carried out: 1) Lethal and sublethal effects of the topical application of FHFSRC at 2% on the first, second, third and fourth larval instars of A. gemmatalis; 2) Lethal and sublethal effects of the application of FHFSRC at 2% in the artificial diet on the first, second, third and fourth larval instars of A. gemmatalis; 3) Ovicidal effect of FHFSRC at 2% on A. gemmatalis eggs; The bioassays included four treatments, namely: treatment 1: distilled water, as a negative control; Treatment 2: synthetic chemical insecticide Assaris®, at a concentration of 0.375 v/v, as a positive control; Treatment 3: FHFSRC at 2%, as a treatment to be tested; Treatment 4: Alcohol 90% v/v, as a negative control. The lethal effect of the treatments was evaluated by monitoring the survival of the caterpillars for 10 days. For sublethal damage, pupal weight, duration of the pupal period, in days, and the percentage of moth emergence were evaluated. In bioassay 3, the ovicidal effect was evaluated by counting the hatching of caterpillars after five days. The data revealed that FHFSRC at 2% reduced the probability of survival of A. gemmatalis caterpillars from the first to the fourth instar, but mainly in the first two instars, thus demonstrating an insecticidal effect. The ovicidal effect was also observed, with FHFSRC at 2% reducing caterpillar hatching by 64.4%. FHFSRC at 2% did not cause significant sublethal effects on A. gemmatalis. FHFSRC at 2% has an ovicidal and insecticidal effect on A. gemmatalis caterpillars, representing a potential bioinsecticide to be used in the management of the pest.