Avaliação dos óleos essenciais de Piperaceae sobre a toxicidade e parâmetros fisiológicos em Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) e efeito sinergista dos seus componentes majoritários

Abstract

The objective of this research was: (i) to obtain and identify the essential oils of Piper corcovadensis, Piper marginatum and Piper arboreum, and evaluation of topical contact toxicity in Spodoptera frugiperda, in addition to the influence of lethal and sublethal doses (LD30-50-70) on nutritional parameters; (ii) to investigate effect of LD50 after exposure time of 48h on histology, morphometry, histochemistry and immunohistochemistry of the midgut and fat body and (iii) to verify toxicity of α-pinene, β-pinene, α- phellandrene, terpinolene and E-caryophyllene their binary mixtures and synergistic effect. In fresh leaf oils were obtained by hydrodistillation. 85 compounds were identified by GC-ME, and E-caryophyllene the major component common to all three species. P. corcovadensis presented a better yield (0.232±0.01%), lower LD50(3.58 mg/g) and DL90(6.34 mg/g), higher toxicity ratios for LD50(3.04) and LD90(8.64), besides altering the amounts of protein, glycogen and total sugar in sublethal (LD30) and lethal (LD50-70) doses. The essential oils promoted deleterious alterations in the midgut of S. frugiperda, being P. corcovadensis provided the increased toxicity, promoting histopathological changes, a reduction in the number of carbohydrates in the midgut, an increase in the apoptotic index (25%) and lower cellular proliferation, different from P. arborerum, which, despite causing similar histopathological alterations to P. corcovadensis, presented a higher rate of cell proliferation and increase of regenerative cells, indicating a more rapid regeneration of the epithelium. The binary mixtures would assume Probit model with values of LD50 and LD90 ranging from 1.66 to 7.75mg/g of insect and 12.78 to 62.98mg/g of insect, respectively. Binary mixtures with terpinolene showed synergism, especially terpinolene+β-pinene which, in addition to the synergic effect, showed a higher toxicity. The combination of α-phellandrene+E-caryophyllene had an antagonistic effect and β-pinene+E-caryophyllene had an additive effect. These observations warrant investigation of the potential effects that essential oils may have on pest insects.