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The fall armyworm, Spodoptera frugiperda, is one of the major field pests for maize production. It is mainly controlled by means of synthetic, and more recently by resistant cultivar of maize expressing Bt toxins. The neem tree, Azadirachta indica, is a plant that can potentially control insects with the advantage of being food and environmental safe. The aim of this study was to assess the effect of neem oil on the development and survival of S. frugiperda caterpillars by assessing histological alterations caused on their midgut. Newly hatched caterpillars were submitted to three neem oil concentrations: 0.006; 0.05; 0.4%, which were added to their artificial diet. Ten 3rd instar caterpillars, taken from each treatment, were submitted to histological analysis. The alimentary canals from the specimens were fixed in Baker for 12 hours, desiccated and diaphanized in alcohol/xylol (1:1) and xylol. After placing the samples in paraffin, they were sliced in 8 µm sections and stained with hematoxylin-eosin stain. The neem oil added to the diet of S. frugiperda caused total mortality at dose of 0.4% whilst still in the first instars, prolonged the larval and pupal stages, and reduced the pupal weight. Histo-physiological alterations such as degeneration of the epithelial lining of the midgut and in the peritrophic matrix were found at all concentrations of neem oil. A lagarta-do-cartucho, Spodoptera frugiperda, é a mais importante praga da cultura do milho. Esta é usualmente, controlada por inseticidas sintéticos e mais atualmente por meio de variedades resistentes de milho com a toxina Bt. O nim Azadirachta indica é planta com potencial no controle de insetos, que possui as vantagens de segurança alimentar e ambiental. Objetivou-se com este estudo avaliar o efeito do óleo do nim no desenvolvimento e sobrevivência de lagartas de S. frugiperda em decorrência das alterações no mesêntero. As lagartas recém nascidas foram submetidas a três concentrações do óleo de nim: 0,006; 0,05; 0,4%, adicionadas à dieta artificial. Dez lagartas do 3º instar, retiradas de cada tratamento, foram submetidas à análise histológica. O canal alimentar dos indivíduos foi fixado em Baker por 12 horas, desidratado, diafanizado em álcool/xilol (1:1) e xilol. Após a inclusão em parafina, as amostras foram seccionadas em 8 µm e coradas pela técnica de hematoxilina-eosina. Observou-se que o óleo de A. indica adicionado à dieta de S. frugiperda causa: mortalidade total na dosagem 0,4% nos primeiros instares, aumento na duração do período larval e pupal, redução no peso de pupas. Alterações histofisiológicas, como degeneração do epitélio do revestimento do mesêntero, da matriz peritrófica foram registradas em todas as concentrações do óleo de neem

The effect of sub-lethal doses of Azadirachta indica (Meliaceae) oil on the midgut of Spodoptera frugiperda (Lepidoptera, Noctuidae)