Avaliação de extratos secos vegetais para o manejo de Callosobruchus maculatus fabr. (1775) (Coleoptera: Chrysomelidae) em feijão-caupi armazenado

Abstract

The beetle Callosobruchus maculatus (Fabr., 1775) (Coleoptera: Chrysomelidae) is considered the main pest of Vigna unguiculata (L.) Walp - Leguminosae (Cowpea) under storage conditions. The use of products of a plant nature, such as powders, aqueous extracts, and oils for the control of agricultural pests have been studied as an alternative for a more sustainable management. Research using vegetable powders is less frequent but of great importance for the small producer, because it has a low cost of preparation, are easy to obtain and use, and do not require skilled labor. The objective of this work was to evaluate the effect of dry plant extract from the leaves of Croton pulegiodorus Baill. – Euphorbiaceae (Velaminho), Momordica charantia L. – Cucurbitaceae (Melon-de-são-caetano) and Sarcomphalus joazeiro (Mart.) Hauenshild – Rhamnaceae (Juazeiro), on mortality, repellency, oviposition and emergence of C. maculatus in stored cowpea. Arenas consisting of plastic pots (140ml), containing 20g of cowpeas, were used, in which the dry extract of each plant was added separately according to the treatments (0g, 1g; 1.5g; 2g; 2.5g and 3g). After assembling the arenas, 10 non-sexed adult insects were inserted, which were confined for 48 hours in B.O.D (28±2°C, 70±5UR and 24h scotophase). For the mortality test, the live and dead insects were counted, then they were discarded and the data obtained were submitted to ANOVA, and the means were compared by Tukey's test (P < 0.05). For the repellency, arenas composed of two plastic containers, symmetrically interconnected by two plastic tubes, to a central container were used. In the two side pots, 20g of cowpea were deposited, adding in one of them the established amount of dry vegetable extract (treatment) and the other, corresponded to the control. In the central box, 10 adult insects of C. maculatus were released in 10 replications. The insects attracted to each treatment were counted, and the Repellency Index (RI) was determined. The beetles were removed and the number of eggs in all grains was counted, which were transferred to small plastic pots (140ml) and taken back to B.O.D. After 30 days of storage, the number of adult insects emerged was counted. The experiments were carried out in a completely randomized design with 10 replications. The results of RI, oviposition and emergence were submitted to Student's t test to determine their statistical significance. The dry plant extract Croton pulegiodorus was the one that showed the best results among all the plants used, it was the only species that caused mortality of the insects with percentages ranging from 58% to 96%. The RI demonstrated that the treatments containing the dry extract of C. pulegiodorus and S. joazeiro were the only ones that presented repellent effect, which significantly interfered in the oviposition and emergence of insects. It was demonstrated that the extracts of the leaves of C. pulegiodorus and S. joazeiro are promising for the management of C. maculatus. On the other hand, M. charantia did not affect the behavior of the pest in any of the experiments performed, being considered neutral.