Bioatividade de extratos vegetais de vitex cymosa e eschweilera pedicellata sobre adultos de sitophilus zeamais motschulsky, 1855 (coleoptera, curculionidae)

Abstract

The problems resulting from application of synthetic insecticides have been amplified due to increasing concern about the sustainability of natural resources and about the well-being of the population and the environment. Taking into account this new philosophy, which tries to harmonize ecological principles with agricultural development, we propose an evaluation of the bioactivity of extracts from the species Eschweilera pedicellata (Lecythidaceae) and Vitex cymosa (Verbenaceae) against adults of Sitophilus zeamais (Coleoptera, Curculionidae), an important pest of stored grains in Brazil. The aqueous extract from leaves of E. pedicellata was the most promising in terms of its repellent effect, followed by the hydromethanolic and aqueous extracts from leaves and the methanolic extract from flowers and stems of V. cymosa. On the other hand, the aqueous extracts from stems of E. pedicellata and the dichloromethane and methanolic extracts from leaves of V. cymosa and the methanolic extract from roots of V. cymosa attracted S. zeamais adults, while the hydromethanolic extract from the roots of V. cymosa was neutral. Depending on the concentration and time variables, most of the individuals responses were not dose dependent and did not vary over the time evaluated. The methanolic extract from stems of V. cymosa resulted in more than a 40% reduction in adult survival when administered by the ingestion method. It also showed a promising estimated value for CL50, and the number of individuals in the F1 generation decreased by approximately 40%. These results made it the most promising among the extracts assessed for their insecticidal properties. Individuals of the S. zeamais used in this study were more sensitive to extracts to which they were exposed by the ingestion, as compared to exposure by contact. Thus, considering results of exposure by ingestion, the methanolic extract from stems and the dichloromethane extract from flowers of V. cymosa achieved good results. For E. pedicellata the best result was observed with the aqueous extract from stems. Furthermore, since the best result in controlling the weevil S. zeamais is achieved when all stages of insect development are controlled, the methanol extract from stems and the dichloromethane extract from leaves and flowers of V. cymosa and, the aqueous extract of the stems of E. pedicellata can be considered to be better candidates than the aqueous extract from leaves of V. cymosa, for which the negative effect was only found for S. zeamais adults. In view of the fact that phytochemical studies were not carried out, it was not possible to associate repellency/attractiveness and mortality with the chemical composition of the extracts. Therefore, we suggest that phytochemical studies in association with new bioassays should be performed with the aforementioned extracts in order to confirm and validate the results obtained in this study.