TOXICITIES OF Annona DERIVATIVES AND SEMI-PURIFIED FRACTIONS AGAINST Zabrotes subfasciatus

Abstract

Background. The Annonaceae botanical family is a promising source of new insecticidal molecules that can be used to protect stored beans against Bruchinae beetles due to its variety of bioactive compounds such as alkaloids and acetogenins. Bruchinae beetles are major pests of stored beans in the world. These beetles feed on stored beans and they promote high levels of damages. Objective. The present study assessed the lethal and sublethal effects of crude ethanolic extracts prepared from different parts (leaves, branches and seeds) of Annona montana, Annona mucosa, Annona muricata and Annona reticulata against the Mexican bean weevil, Zabrotes subfasciatus (Boehman). Methodology. It was performed toxicological bioassays by spraying ethanolic extracts and fractions from Annona species on grains surface. The treated grains were infested with adults of Z. subfasciatus. It was evaluated the number of dead insects, eggs, F1 progeny and damaged grains. Ethanolic extracts obtained by cold maceration [ratio 1:5 (v p-1)] were applied on grains surface (cv. Bolinha) at 1,500 ppm [extract (mg) grains (kg)-1]. Results. The seed extract from A. mucosa promoted 100% of mortality of Z. subfasciatus and completely inhibited the oviposition, the F1 progeny emergence and the damage on grains. In addition, it was also estimated the LC50 of the ethanolic extracts from seeds of Annona species. Interestingly, lethal concentrations varied according to Z. subfasciatus sex, and females supported higher doses than males. The ethanolic extract from seeds of A. mucosa presented the lowest LC50 value (571.82 mg kg-1) among all extracts. Thereby, it was submitted to liquid-liquid partition producing a hexane fraction and a remaining hydro-methanol phase. The former fraction killed 100% of insects whereas the later killed 20% of insects, but both of them promoted sublethal effects on Z. subfasciatus reducing the number of eggs and F1 progeny. Implication. The ethanolic extracts of A. mucosa, A. montana, A. muricata and A. reticulata can be used as raw material for the formulation of a botanical insecticide that can help small farmers. Conclusion. The ethanolic extracts from seeds of A. mucosa, A. montana, A. muricata and A. reticulata are highly toxic to Zabrotes subfasciatus and protected the stored beans.