Insecticidal activity of Varronia curassavica Jacq essential oil. (Boraginaceae) on larvae of Aedes spp. (Diptera: Culicidae)

Abstract

Synthetic chemical insecticides are still widely used as the primary method of controlling the mosquito Aedes aegypti, the main vector of dengue, chikungunya, urban yellow fever, and Zika viruses. Although effective, these products cause serious environmental damage and pose risks to human health. As an alternative, botanical insecticides have gained attention for their lower toxicity. This study evaluated the larvicidal potential of the essential oil of Varronia curassavica Jacq. (commonly known as "erva-baleeira") against Aedes spp. larvae. Bioassays were conducted using 20 larvae per disposable cup, each containing 25 mL of essential oil solutions at four different concentrations, with four replicates per concentration. A positive control with the synthetic insecticide pyriproxyfen (0.00001%) and a negative control with distilled water were used. Dimethyl sulfoxide (DMSO) at 1% was used as an emulsifier. Chemical analysis of the oil showed a predominance of sesquiterpenes, with (E)-caryophyllene as the major compound, followed by bicyclogermacrene and δ-cadinene. At the highest concentration (0.125%), the oil caused 100% larval mortality within 24 hours. At 0.0625%, mortality rates were 77.5% (24h), 96.3% (48h), and 100% (72h). At 0.0312%, mortality was 63.7% (24h), 90% (48h), and 95% (72h). At the lowest concentration (0.0156%), mortality rates were 37.5%, 51.2%, and 25.5% over the same time intervals. These results highlight the promising larvicidal effect of V. curassavica essential oil in controlling Aedes spp., especially considering the novelty of this data for this plant species.