Bioinsecticidal potential of Baeckea frutescens (Myrtales: Myrtaceae) essential oil: chemical variation, yeast encapsulation, and larvicidal activity against Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus (Diptera: Culicidae).

Abstract

Plant essential oils are promising alternatives to synthetic larvicides, but their development is often limited by chemical variability, formulation challenges, and concerns regarding non-target toxicity. Baeckea frutescens, a widespread weed species, remains insufficiently characterized in terms of chemotypic diversity, stereochemical composition, and larvicidal selectivity. The essential oils were dominated by mono- and sesquiterpenoids, with p-cymene, 1,8-cineole, α- and β-pinene, α-humulene, caryophyllene oxide, and humulene epoxide II as major constituents. PCA and HCA revealed distinct chemotypic groups that may reflect temporal variation in essential oil composition. Chiral GC analysis showed pronounced enantiomeric excess for several terpenoids. In WHO-based larvicidal assays, free essential oils exhibited notable activity against Aedes aegypti (Linnaeus), Aedes albopictus (Skuse), and Culex quinquefasciatus Say (Diptera: Culicidae). The corresponding 24-h LC50 values ranged from 18.97 to 39.33 µg/mL, 10.60 to 13.11 µg/mL, and 19.79 to 45.62 µg/mL, respectively. Yeast encapsulation achieved a loading capacity of approximately 11.1% to 40.71% and retained larvicidal activity in acute assays. This study provides integrated chemotypic and enantiomeric insights into B. frutescens essential oil and demonstrates its acute larvicidal activity with preliminary indication of selectivity against multiple mosquito species using WHO-based protocols. The findings support the sustainable utilization of an underutilized weed species and provide a chemically informed basis for the development of sustainable botanical larvicides.