Abstract
Although the insecticidal properties of some plant essential oils are well-documented, their use in integrated pest and vector management is complicated by their high volatility, low thermal stability, high sensitivity to oxidation, and low solubility in water. We investigated the use of bio-based N-1-hexadecylammonium chloride and sodium palmitate amylose inclusion complexes as emulsifiers for two essential oils, garlic and asafoetida, known to be highly toxic to mosquito larvae. Four emulsions of each essential oil based on amylose hexadecylammonium chloride and amylose sodium palmitate inclusion complexes were evaluated for their toxicity against Aedes aegypti L. larvae relative to bulk essential oils. All emulsions were significantly more toxic than the bulk essential oil with the lethal dosage ratios ranging from 1.09–1.30 relative to bulk essential oil. Droplet numbers ranged from 1.11 × 109 to 9.55 × 109 per mL and did not change significantly after a 6-month storage period. These findings demonstrated that amylose inclusion complexes enhanced the toxicity of essential oils and could be used to develop new essential oil based larvicides for use in integrated vector management.
Highlights
Essential oils are complex mixtures of volatile compounds produced by aromatic plants through secondary metabolic pathways
The toxicities of garlic and asafoetida essential oils were significantly higher when both Hex-Am and Na-P inclusion complexes were used as emulsifiers compared to bulk essential oil (Table 1)
Aqueous emulsions of garlic and asafoetida essential oils were prepared using the two emulsifiers and their toxicity against mosquito larvae determined. Both essential oils are known to be highly toxic to mosquito larvae, as depicted by their low LC50 values [38,39], but their low solubility in water complicates their application in pest and vector management
Summary
Essential oils are complex mixtures of volatile compounds produced by aromatic plants through secondary metabolic pathways. Essential oils produce a wide range of biological effects ranging from direct lethal effects against all four life stages (i.e., eggs, larvae, pupae, and adult) to oviposition deterrent and repellent activity against adult mosquitoes [9,10,11,12,13,14]. These oils have emerged as a promising tool for combating insecticide resistance because they possess complex mixtures of bioactive compounds with different modes of action. They can enhance the toxicity of synthetic insecticides [15,16,17]
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