Atividade insetistática de pós de origem vegetal sobre Sitophilus zeamais Motschulsky (1855) em milho armazenado

Abstract

Corn is one of the main agricultural crops in Brazil, as it is used to several by-products, fact that contributes to its comercial value and the economic movement in the country. It is an energetic aliment which has high nutricional value and is easy accessible, been part of human and animal diet. However, there are considerable damages due the attack of pest insects, mainly caused by Sitophilus zeamais Motschulsky, 1855 (Coleoptera: Curculionidae), which has great agricultural importance, for attacking in the field and in the warehouses, in addition to destroying the healthy grain, taking the chance to ovoposit, being considered, therefore, internal primary pest. This pest control is carried out with synthetic insecticides, however, its use is harmful to the environment, besides human and animal heath. The use of vegetable origin powders has been shown to be effective against stored grain pests, moreover, it is easy to obtain and use, also being within the range of the small farmer. The aim of this paper was to evaluate the toxicity and repellency of five powders of vegetable species on S. zeamais. Leaves of Croton pulegiodorus (Velaminho), Momordica charantia (Melão-de-São-Caetano), Azadirachta indica (Nim), Prosopis juliflora (Algaroba) e Ziziphus joazeiro (Juazeiro) were dried and ground, separately, to obtain a refined powder, subsequently applied to samples of corn kernels, in different powder amounts (0g, 1g, 2g, 3g, 4g, 5g), contained in Petri dishes (mortality assessment) and in interconnected flasks (repellency assessment). Each treatment was infested with 10 non-sexed adult insects, using six replications in a completely randomized design, at room temperature. All experiments were evaluated after a period of 72 hours. Only C. pulegiodorus caused high insect mortality (76.67% to 100%), being extremely low when in contact with other plants (0% in Z. joazeiro to 26.67% in A. indica). In addition, the mortality caused by A. indica was higher than that of the control only in the 3g amount of powder, while the other species (P. juliflora, Z. joazeiro and M. charantia) did not differ from the control and neither among themselves. It was observed that only C. pulegiodorus had a repellent action, as the other plants were considered neutral. These results demonstrate that the dry extract (powder) of velaminho (C. pulegiodorus) is a promising alternative for the management of S. zeamais in stored corn as it has biological activity on this coleopteran.