ABSTRACT
Agricultural pest control is a popular research topic, and essential oils are widely studied because they represent a promising alternative to synthetic insecticides. However, despite the increase in studies on pests, little work has been done on pesticide contamination of the predators feeding on insecticide-affected prey. Therefore, the objective of this study was to evaluate the effects of Lethal Dose 50 (LD50) from the essential oils of Mentha spicata L. and Melaleuca alternifolia Cheel on the histology, including histochemistry (from protein and carbohydrate analysis) and immunohistochemistry (from the evaluation of cellular apoptosis), of the midgut of fifth instar nymphs of Podisus nigrispinus (stinkbug) (Dallas). The periods of analysis were 12, 24, and 48 h after ingestion of Alabama argillacea Hübner caterpillars treated with the respective oils. The oil from M. spicata did not cause histological alterations or apoptosis in the insect. However, there was a reduction in the level of carbohydrates within the 48-h period. After 24 h, the oil of M. alternifolia caused an elongation of digestive cells and, after 48 h, cell lysis with the release of material into the lumen, suggesting tissue necrosis. The immunohistochemical study revealed no apoptotic process. There was a reduction in the neutral carbohydrate levels in the 24- and 48-h periods and in the number of regenerative cells, when compared to the control, after the period of 48 h. These results demonstrate that M. spicata oil has potential for use in cotton fields because it does not affect the vital characteristics of P. nigrispinus. However, the essential oil of M. alternifolia is not suitable for use as a pesticide because it is extremely toxic to predators.
