Modification of yeast-encapsulated essential oil-based larvicides for stability and extended-release

Climate change is shifting the geographical distribution of disease-carrying mosquitoes, leading to mosquito-borne disease (MBD) outbreaks in previously unaffected regions globally. The absence of vaccines and treatments for MBDs underscores the critical need for effective vector control strategies. While larval source management plays a crucial role in controlling mosquito populations, larvicides that are currently on the market are hindered by resistance development and environmental concerns. In previous work, we encapsulated orange oil (Citrus sinensis) into Bakers’ yeast (Saccharomyces cerevisiae) and demonstrated the efficacy of the yeast-encapsulated orange oil (YEOO) microcapsules against laboratory and insecticide-resistant strains of Aedes aegypti larvae. However, these microcapsules lose their effectiveness within 48 hours, likely due to microbial contamination at mosquito breeding sites. Our current work focuses on YEOO microcapsule modification to extend their effectiveness and stability in water, as well as the development and testing of extended-release formulations. Microcapsules were individually coated with alginate and/or chitin to extend their durability as well as to increase the larvicide palatability to mosquito larvae. Extended-release formulations were developed by encasing bulk microcapsules in alginate beads. As the alginate swells and crosslinks break, YEOO is released over time. Coated larvicide and YEOO-encased beads were analyzed by FTIR and Raman spectroscopies, optical and electron microscopy, and larvicidal assay. Release kinetics for extended-release formulations are measured by direct microcapsule counting and fluorescence analysis while long-term efficacy is evaluated by larvicidal assay. These improvements to current YEOO formulations are expected to significantly enhance its efficacy and sustainability for larval source management.