Bioatividade de extratos vegetais sobre Spodoptera frugiperda (J. E. Smith) (Lepidoptera: noctuidae)

Abstract

Spodoptera frugiperda, key pest of maize, has been controlled by chemical products, which are effective but cause environmental disturbances. The insecticide effect of aqueous extracts for control of S. frugiperda it was studied. Thus, leaves and stems of 'algodão-de-seda', Calotropis procera (Ait), physic- nut Jatropha curcas (L.), citronella, Cymbopogon nardus (L.), 'juá', Zizyphus joazeiro (Mart.), 'noni', Morinda citrifolia (L.), 'tingui', Magonia pubescens (A.St.Hil.), and sugar apple, Annona squamosa (L.) were collected in Janaúba, MG. The samples were washed, dried and ground into slicer. The obtained powder was put in glass, covered with foil and stored in refrigerator. With that powder were made aqueous extracts at 10%. For extracting water soluble compounds, the extracts stayed in refrigerator for 24 hours. After that, the extracts were filtered and added to artificial diet of S. frugiperda that was poured into sterile glass tubes and enclosed with water repellent cotton. In every tube, separated per treatment, was put a first instar larva of S. frugiperda. All the experiments stayed in laboratory (temperature of 25 ± 1 °C, RH 70 ± 10% and photoperiod of 14 hours) Daily, they were evaluated larva mortality and occurrence of pupae, that 24 hours after their formation were sexed, weighed and individually put in new tubes where stayed until adult emergence In the first experiment, four treatments were evaluated, extracts of sugar apple, algodão-de-seda', citronella and "jua', plus one control without extract. In the second one, three treatments, extracts of 'noni", "tingui' and physic-nut, plus a control without extract. In the third experiment, five treatments, aqueous extracts of algodão-de-seda, citronella, 'juá', 'noni and sugar apple, and a control without extract. It was also performed another experiment with three treatments plus control, where the plant extracts were applied on maize leaves. For that, the leaves were immersed for 10 seconds in extracts of sugar apple, 'noni' or 'algodão-de-seda'. All of the experiments were conducted in a completely randomized design and consisting of 50 repetitions (tube), in which one armyworm was inoculated a first instar larva of S. frugiperda. All obtained results, separate per experiments, were subjected to analysis of variance and means were compared by the Tukey test at 5% probability. In all the experiments were evaluated variables duration of larval and pupal phases, weight of male and female pupae, deformation of pupae and adults. In the first experiment, the intake by armyworm S. frugiperda of diets with different aqueous plant extracts significantly affected the larval and pupal duration, and caused high larva mortality. As for male and female pupae, only the extract of juá decreased de their weight. In the second experiment, the ingestion of extracts of 'noni increased increased larval mortality, but did not alter the larva duration. In the third experiment, high larva mortality was observed when the armyworms were fed with diets containing sugar apple, r noni' or 'algodão-de- seda The consumption of leaves impregnated with different plant extracts ton of leaves raised larva mortality and significantly decreased the pupa weight, which was greater for sugar apple treatment 1. The sugar apple extract, 'noni' and 'algodão- de-seda showed higher insecticide activity on the armyworm of S. frugiperda. but the sugar apple extract was the most effective one.