Characterization and bioassay for larvicidal activity of Anacardium occidentale (cashew) shell waste fractions against dengue vector Aedes aegypti.

Recent studies regarding the harmful effects of synthetic larvicides initiated the need to investigate for unconventional measures that are environmentally safe and target-specific against Aedes aegypti larvae. Thus, the main objectives of the study are to evaluate the larvicidal toxicity of the solvent fractions of Anacardium occidentale shell wastes against the third and fourth instar larvae of A. aegypti and to compare the results with the commercial larvicide product. The shell wastes were extracted with 95% EtOH followed by polarity-based fractionation. The fractions were tested for larvicidal activity according to the World Health Organization bioassay method. These were then characterized by quantitative thin-layer chromatographic (TLC) fingerprinting. The hexane fraction gave the strongest activity among the fractions with an LC50 of 4.01 mg/L and LC90 of 11.29 mg/L highly comparable to the commercial larvicide, which exhibited an LC50 of 1.71 mg/L and LC90 of 8.41 mg/L. The dichloromethane fraction exhibited 9.70 mg/L LC50 and 18.44 mg/L LC90. The remarkable toxicity effects exhibited by these fractions indicate their potential to provide core structures from which sustainable and environmentally safe plant-based larvicidal agents can be synthesized.

Larvicidal activity of Persea americana Mill. against Aedes aegypti.

OBJECTIVE: To evaluate the toxicity of the ethanol and hexane extracts of the different parts of Persea americana Mill. (P. americana) toward third and fourth instars larvae of Aedes aegypti (Ae. aegypti) and to characterize the ethanol extract by qualitative phytochemical analysis. METHODS: The seeds, peels and pulp of P. americana were processed for crude extraction using 95% ethanol and n-hexane. Crude extracts were bio-assayed for larvicidal activity against Ae. aegypti following the World Health Organization standard bioassay method. The mortality was observed at 24 h and 48 h after treatment and data were subjected to probit analysis to determine lethal concentrations (LC50 and LC90). The ethanol extract was characterized by phytochemical analysis. RESULTS: Both the hexane and ethanol extracts from the different parts of P. americana exhibited evidence of larvicidal toxicity. The hexane extract from the seeds exhibited the highest toxicity with LC50 and LC90 values of 9.82 mg/L and 22.19 mg/L, respectively, while the ethanol seed extract exhibited LC50 of 16.48 mg/L and LC90 45.77 mg/L, respectively. This was closely followed by the ethanol extract of the peels with an LC50 of 10.35 mg/L and LC90 of 26.29 mg/L. The pulp extracted with ethanol also yielded great larvicidal toxicity with LC50 of 21.32 mg/L and LC90 of 59.45 mg/L. Results of the phytochemical analysis of the ethanol seed extract indicated presence of alkaloids, tannins, saponins, unsaturated steroids and triterpenoids, flavonoids (leucoanthocyanins), fats and oils. CONCLUSIONS: Both the hexane and ethanol extracts of P. americana showed promising potential as an alternative source of a more sustainable, non-toxic and environmentally friendly solution for the control of dengue vector, Ae. aegypti.