Essential oil toxicity on biological and reproductive parameters of Alabama argillacea (Hübner) (Lepidoptera: Erebidae).

Several studies have demonstrated the effects of essential oils on insect pests. These effects vary and affect fundamental parameters for the survival of these organisms. However, there is a scarcity of research on the effect of these substances on Alabama argillacea (Hübner) (Lepidoptera: Erebidae), the main defoliating pest of cotton (Gossypium hirsutum L.). Thus, the present study aimed to evaluate the activity of essential oils from Litsea cubeba (Lour.) Pers., Melaleuca alternifolia Cheel, Juniperus virginiana L., and Mentha spicata L., on the biological and reproductive parameters of A. argillacea and the consequent effects on the gonads of both males and females of this pest. All essential oils presented toxicity by contact in third instar larvae of A. argillacea, causing a reduction in the weight of larvae and pupae, as well as affecting the number and viability of eggs. These essential oils changed the histochemistry of the testicles, and M. alternifolia, J. virginiana, and M. spicata also affected their morphology. The histochemistry of the ovarioles was altered by the essential oils from M. alternifolia, J. virginiana, and L. cubeba. Thus, the essential oils tested in the present work are promising for the control of A. argillacea, as they are toxic and affect the development and reproduction of this key pest of cotton.

Effect of essential oils of Mentha spicata L. and Melaleuca alternifolia Cheel on the midgut of Podisus nigrispinus (Dallas) (Hemiptera: Pentatomidae).

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.