Atividade inseticida dos extratos das sementes de tamboril (Enterolobium contortisiliquum (VELL.) MORONG) sobre o Aedes aegypti (Diptera: Culicidae)

Abstract

Synthetic chemical insecticides are the main way to control Aedes aegypti. However, its use has several limitations, including environmental toxicity, risk to human health and selection of insecticide-resistant insect populations. Such factors favor the growing search for natural substances with insecticidal properties. This study evaluated the insecticidal activity of crude extracts of Enterolobium contortisiliquum (Vell.) seeds on eggs and larvae of A. aegypti and verified the phytochemical profile and the presence of lectins in the extract. E. contortisiliquiim has a wide geographic distribution in Brazil. Its seeds are known for their toxicity, medicinal properties, and bioactive proteins. The extraction of the bioactive compounds was performed in 0.15 M NaCl salt solution, for its ability to solubilize these molecules. To prepare the crude extract, twenty grams of the powder obtained from crushing the seeds were homogenized for 4 hours at 25º, in 200 mL of saline solution. A. aegypti eggs were obtained by capture with ovitrap-type traps. The larvae were hatched and kept in a B.O.D. (Biochemical Oxygen Demand) with a temperature of 25±1°C, relative humidity of 70±10% and a 12 hour photophase. For tests with eggs and larvae of A. aegypti, the crude extract was used in raw form (Raw Crude Extract - RCE) and boiled (Boiled Crude Extract - BCE) at 100º C for 5 min. Concentrations of 4.68; 9.37; 18.75; 28.13; 37.13 and 46.89 mg/mL, with distilled water as a negative control. Assays were performed in triplicate. Larvicidal activity tests were performed in the B.O.D. The data were submitted to analysis of variance, Shapiro-Wilk Test, Tukey Test and Log-Probit analysis to determine the LC50 and 90 of the extracts. BCE showed better results on eggs than RCE, managing to prevent the hatching of larvae in 81.66% ± 10.40 of treated eggs, at a concentration of 46.89 mg/mL. Increased concentration improved ECB's results against eggs. The respective LC50 and 90 were set at 35.95 and 52.67 mg/mL, respectively. In tests with larvae, concentrations of 46.89 and 37.13 mg/mL, for RCE and BCE, caused 100% mortality in 24 hours of exposure. Increased concentration improved RCE and BCE action. Larval mortality at other concentrations increased with increasing exposure time to 48 h. Concentration and time alone, as well as their interaction are significant factors for the larvicidal activity of the extracts (p<0.001). Due to its better total efficiency (E=72.77), RCE, with 48 h of exposure, is the most promising extract on larvae. 10.86 mg/mL of RCE after 48 h of exposure is the lowest dose capable of killing 90% of the larvae (LC90). In RCE, the presence of lectins and secondary metabolites: flavonoids, xanthones and phenols, were detected. The results demonstrate the potential of E. contortisiliquum seed extracts in the ovicidal and larvicidal action on A. aegypti.