Bioatividade de extratos etanólicos de Croton sobre Plutella xylostella (L) e ação fumigante e composição química de óleos essenciais de Croton grevioides (Baill.) sobre Zabrotes subfasciatus (Boheman)

Abstract

Plants constitute natural sources of insecticide substances and have been used by mankind since Antiquity. It is also known that medicinal plants present great quantities of secondary compounds such as alkaloids, terpens, flavonoids and steroids which promote high resistance to the onset of pests and diseases. The genus Croton, which is made up of species that occur naturally in the State of Pernambuco, where many of them are used in the popular medicine and characterize themselves by the production of essential oil, owns expressive relevance founded on their sources of fixed and volatile components with recognized biological activity in the treatment of various illnesses. The knowledge that medicinal plants present high resistance to the onset of diseases and pests has led us to investigate the potential insecticide of crude ethanolic extracts from different parts of plants of the genus Croton against Plutella xylostella L. and of the essential oil of the species C. grewioides against Zabrotes subfasciatus Boheman. All the investigated plants are native to the biome in Pernambuco with use in the popular medicine by the community where its occurrence is reported. The crude extracts were obtained through cold maceration, ethanol being used as solvent, from leaves and stalks of the species Croton jacobinensis Baill, C. micans Muell., C. rhamnifolius H.B.K and C. sellowii Baill. The essential oil, on the other hand, was obtainedthrough hydro-distillation from the leaves and stalk of C. grewioides. These extracts were diluted into previously determined concentrations by means of a pilot experiment and their activities were tested for the development and survival of Plutella xylostella L. To do so, with the aid of Potter’s Tower, eight-cm diameter cabbage disks, Brassica oleracea var. acephala L., were ground with different concentrations of the ethanolic extracts and offered to caterpillars confined into Petri’s dishes. Among the studied extracts, the ethanolic extract from leaves of C. rhamnifolium was the most toxic at the larval phase, followed by the ethanolic extract from the stalk of the same species, presenting CL50 of 14.95 and 42.40μg mL-1, respectively. The interference of the extract of C. rhamnifolius in the development of P. xylostella was also noticed. From the stalk and leaves of Croton grewioides Baill essential oils were extracted through hydro-distillation and then analyzed by GC/MS. This analysis revealed that both oils are made up of 22 compounds, in which the predominant chemical class was that of the phenylpropanoids, whose major representative was (E)-anetol (65.5% in the leaves and 47.8% in the stalk). The fumigant effect of both essential oils was assessed for the woodworm of beans, Z. subfasciatus, which presented itself as potential for the control of this pest. The essential oil of leaves presented itself about 3.4 times more effectivethan the essential oil from the stalk and the estimated values for the CL50 were 4.0 and 13.7 μg mL-1 of air, respectively.