Avaliação da actividade insecticida dos extratos de Trichilias emetica, Trichilia capitatae Azadirachta indica, sobre a lagarta do funil de milho (S. frugiperda) na cultura de milho (Zea mays)

Abstract

Spodoptera frugiperda, commonly known as Fall Armyworm, is a pest native to the American continent, which since its introduction to the African continent; has been responsible for high yield losses in the corn crop. In Mozambique, losses in the order of 50% of corn yield caused by this pest have already been reported. Due to its great migratory power, this pest is already widespread in all the provinces of the country. To date, synthetic insecticides have been used to contain infestation by this pest. However, these insecticides, in addition to causing serious environmental problems, have been responsible for the emergence of resistant biotypes of these pests. One of the most effective ways to control this pest is the use of botanical insecticides. In addition to their proven effectiveness, these insecticides can mainly benefit the small farmer, because they are easy to use, not requiring qualified personnel, they are more accessible, and do not affect the environment. The present work had as main objective the evaluation of the insecticidal activity of aqueous and ethanol extracts of leaves and stem bark of T. emetica and T. capitata, in comparison with aqueous and ethanol extracts of A. indica leaveson fall Armyworm. For this purpose, aqueous and ethanol extracts of leaves and stem bark of T. emetica and T. capitata, and aqueous and ethanol extracts of A. indica leaves were prepared using sohxlet, in concentrations of 1% to 0.01% (w / v). Through immersion, third instar larvae of Spodoptera frugiperda from the breeding were fed with corn leaves treated with these extracts, using distilled water and 96% ethanol as control. Phytochemical tests were also carried out on the extracts in order to identify the primary and secondary metabolites that are responsible for the insecticidal activities, and the result revealed the presence of alkaloids, flavonoids, tannins, anthraquinones, steroids and terpenoids, glycosides, reducing sugars and amino acids and proteins. The results of the biological tests with the plant extracts showed a strong insecticidal action of the three plants tested, depending on their concentrations, with particular emphasis on the aqueous extract of T. capitata bark, with LD 50 equal to 0.051%.