Dracaena angolesnsis leaf extract as a botanical mosquitocide: bioefficacy against Aedes aegypti, voltage-gated sodium channel (kdr) gene expression, and ecotoxicological evaluation in Danio rerio

Vector-borne diseases transmitted by Aedes mosquitoes remain a major global public health concern. With the growing incidence of insecticide resistance and the potential environmental hazards posed by chemical insecticides, the development of effective green and eco-friendly alternatives to chemical products for the control of mosquito-borne diseases is of paramount importance. The objective of this research work was to investigate the mosquitocidal activities of Dracaena angolesnsis leaves and associated expression of resistance-related genes and their toxicity against Aedes aegypti mosquitoes. Phytochemical screening revealed the presence of several bioactive compounds, including flavonoids, phenols, terpenoids, sterols, tannins, and alkaloids, which are known for their insecticidal potential. Larvicidal, pupicidal, and adulticidal bioassays demonstrated significant mosquito mortality across different solvent extracts, with aqueous and methanol extracts exhibiting the highest efficacy. The lowest larval LC₅₀ value was observed for the aqueous extract (12.97 ppm), while strong pupicidal and adulticidal activities were also recorded. RT-qPCR analysis of the voltage-gated sodium channel (kdr) transcript revealed marked upregulation in treated larvae, with expression levels increasing from 90.65-fold to 10,524-fold relative to untreated control larvae from the same laboratory-maintained field strain. Complete adult mortality (100%) was recorded at 250 and 500 ppm following a 24 h recovery period, and high larval mortality (91.2 ± 1.8% at 24 h, reaching 100% by 48 h at 500 ppm) was achieved despite the significant induction of kdr transcripts, indicating that the multi-target botanical extract effectively suppressed mosquito survival. However, 100% mortality of larvae was observed despite high Knockdown resistance, indicating that the extract was effective in overcoming the resistance-related defense mechanisms. In order to evaluate the environmental safety of the extract, non-target toxicity was investigated in adult zebrafish ( Danio rerio ) exposed to concentrations ranging from 31.25 to 500 ppm over a 96 h period. The extract elicited only mild, concentration-dependent behavioural alterations at the highest tested concentration (500 ppm) including transient changes in swimming orientation and social schooling with zero mortality or structural deformities recorded across all tested concentrations. These results indicate that D. angolesnsis has a high potential to be used as an insecticidal plant for mosquito control.