Toxicidade de extratos de grãos de café verde e torrado de qualidade inferior para larvas de Aedes (=Stegomyia) aegypti (Diptera: Culicidae)

Abstract

The control of Aedes aegypti has been carried out through synthetic chemical insecticides. However, several cases of the selection of resistant populations have been recorded. Thus, botanical products have emerged as a promising alternative for the management of this vector insect, as they exhibit multifaceted interactions with their target sites and low environmental contamination. The objective of the present study was to evaluate the toxicity of extracts from green and inferior-quality roasted coffee for A. aegypti larvae. The coffee extracts were obtained using the solid-liquid reflux technique with methanol as the solvent, and the characterization of the compounds present was done through High- Performance Liquid Chromatography (HPLC). The effects of green coffee extract with DMSO® (CVD), green coffee extract with Tween 80® (CVT), roasted coffee extract with DMSO® (CTD), and roasted coffee extract with Tween 80® (CTT) on A. aegypti were evaluated. These treatments were tested at various concentrations (4, 2, 1.6, 1.2, 1, 0.45, 0.25, and 0.12 mg/mL). Control treatments included chlorine-free water, 1% DMSO, and 1% Tween 80. The bioassay, in a completely randomized design, consisted of 15 third-instar A. aegypti larvae for each treatment, obtained from the laboratory breeding, with four replications, each represented by one larva. Mortality was assessed at 24, 48, and 72 hours after the addition of the extracts to estimate the lethal dose (LD) required to kill 50, 90, and 99% of the larvae. The effect of the major compound (caffeic acid) was also evaluated using the same protocol as for the extracts. The major compounds, in order of highest concentration found in the extracts, were caffeic acid, chlorogenic acid, and catechin (only in roasted coffee extracts). At 72 hours, CTT (4 mg/mL) caused 99.2% mortality, followed by 83.3% for CVD and 55% for CVT. The CTD extract (2 mg/mL) caused 73.3% mortality. The estimated LD50 for CTT was 0.33 ± 0.22 mg/mL, followed by 1.43 ± 0.05 for CTD, 2.53 ± 0.1 for CVD, and 2.57 ± 0.25 for CVT. Isolated caffeic acid caused low mortality at a concentration of 6.42 mg/mL. We conclude that coffee extracts are toxic to A. aegypti larvae, while isolated caffeic acid exhibits low mortality, suggesting the occurrence of synergy with other compounds in the extracts. Further research is needed to better understand the compound's action in the environment and its synergy with other components of coffee extracts.