Estudo fitoquímico e atividade inseticida de Annona crassiflora Mart., Annona mucosa (Jacq.) Baill. (Annonaceae), Dioscorea rotundata Poir (Dioscoreaceae) E Chenopodium ambrosioides L. (chenopodiaceae) em Plutella xylostella (Linnaeus, 1758) (Lepidoptera: Plutellidae)

Abstract

Proposing to find alternative management methods for diamondback moth Plutella xylostella (Lepidoptera: Plutellidae), this study aimed to estimate the lethal concentrations (CL50 and CL99), perform bioguided phytochemical study of the methanol and ethanol extract of Annona crassiflora Mart. and Annona mucosa Jacq. (Annonaceae) seeds and aqueous extracts of the aerial parts of Dioscorea rotundata Poir. (Dioscoreaceae) and Chenopodium ambrosioides L. (Chenopodiaceae) and evaluate the chemical constituents and the insecticidal activity in P. xylostella. Estimation of (CL50 and CL99) was obtained from the formula of Finney (1971) carried out through Probit analysis. For A. crassiflora, concentrations were 0.0009 g.mL-1and 0.029 g.mL-1, and for A. mucosa, 0.00004 g.mL-1and 0.0005 g.mL-1, respectively, being positively active to P. xylostella caterpillars. Partitions originated from extraction with chloroform (CHCl3) were the most active in lethality tests with mortality recorded for A. crassiflora of 84% and 89% for A. mucosa. After assessing activity, partitions were submitted to fractionation on a silica column and A. crassiflora and A. mucosa fractions obtained from the mixture of hexane and chloroform solvents (HEX: CHCl3) (1:1) were found to be more active and cause 84 and 74% mortality, respectively. The mortality bioassay conducted with fractions derived from Medium-Pressure Liquid Chromatography (MPLC) at concentration 0.00184% (CL25) resulted in fractions with a mixture of hexane and acetate, in which the (HEX:ACOET) (3:7) fraction of A. crassiflora species reported mortality of 55% and the (HEX:CHCL3) (1:1) 39-45 fraction of A. mucosa of 72%. Purification of A. mucosa fractions derived from (MPLC), combined with analysis in NMR resulted in the identification of squamocin acetogenin. The estimate of (LC50) of D. rotundata and C. ambrosioides aqueous extracts were 0.0014 g.mL-1 and 0.006 g.mL-1 and ethanol extracts were 0.0352 g.mL-1 and 0.4 g.mL-1. Regarding the insecticidal activity evaluation, both species and types of extracts were considered positively active to P. xylostella caterpillars; however, aqueous extracts were more active. In the analysis of the chemical constituents of D. rotundata and C. ambrosioides, the presence of tannins, flavones, flavonols, xanthones, catechins and saponins was observed in both species. Thus, derivatives of A. crassiflora and A. mucosa seeds have shown to be effective in controlling P. xylostella, and D. rotundata and C. ambrosioides aqueous extracts can be considered efficient biopesticides to control the insect-pest under study.