Abstract
BackgroundEffective mosquito control approaches incorporate both adult and larval stages. For the latter, physical, biological, and chemical control have been used with varying results. Successful control of larvae has been demonstrated using larvicides including insect growth regulators, e.g. the organophosphate temephos, as well as various entomopathogenic microbial species. However, a variety of health and environmental issues are associated with some of these. Laboratory trials of essential oils (EO) have established the larvicidal activity of these substances, but there are currently no commercially available EO-based larvicides. Here we report on the development of a new approach to mosquito larval control using a novel, yeast-based delivery system for EO.MethodsFood-grade orange oil (OO) was encapsulated into yeast cells following an established protocol. To prevent environmental contamination, a proprietary washing strategy was developed to remove excess EO that is adsorbed to the cell exterior during the encapsulation process. The OO-loaded yeast particles were then characterized for OO loading, and tested for efficacy against Aedes aegypti larvae.ResultsThe composition of encapsulated OO extracted from the yeast microparticles was demonstrated not to differ from that of un-encapsulated EO when analyzed by high performance liquid chromatography. After lyophilization, the oil in the larvicide comprised 26–30 percentage weight (wt%), and is consistent with the 60–65% reduction in weight observed after the drying process. Quantitative bioassays carried with Liverpool and Rockefeller Ae. aegypti strains in three different laboratories presented LD50 of 5.1 (95% CI: 4.6–5.6) to 27.6 (95% CI: 26.4–28.8) mg/l, for L1 and L3/L4 mosquito larvae, respectively. LD90 ranged between 18.9 (95% CI: 16.4–21.7) mg/l (L1 larvae) to 76.7 (95% CI: 69.7–84.3) mg/l (L3/L4 larvae).ConclusionsThe larvicide based on OO encapsulated in yeast was shown to be highly active (LD50 < 50 mg/l) against all larval stages of Ae. aegypti. These results demonstrate its potential for incorporation in an integrated approach to larval source management of Ae. aegypti. This novel approach can enable development of affordable control strategies that may have significant impact on global health.
Highlights
Effective mosquito control approaches incorporate both adult and larval stages
Larvicide analysis Micrographs of larvicide particles labeled with Nile Red show that the individual cells are intact and essential oils (EO) is incorporated within the cells (Fig. 1)
Analysis of orange oil (OO) by high performance liquid chromatography (HPLC) before encapsulation yielded a composition of 89.6% d-limonene, 2.4% myrcene, and 1.6% γ-terpinene with 8.2% other minor components, which is consistent with previously reported compositions [26, 27]
Summary
Effective mosquito control approaches incorporate both adult and larval stages. Mosquito-borne diseases are a global threat to human health, implicated in over 1.2 million deaths annually [1]. Among these, those increasing at the fastest rate are the arboviruses dengue, chikungunya and Zika. Workman et al Parasites Vectors (2020) 13:19 health responses have focused on preventing transmission by reducing vector populations These arboviruses are transmitted by the Aedes aegypti mosquito, a vector presenting formidable challenges to disease control. Current approaches to control adult Ae. aegypti relying on insecticide spraying in urban areas pose risks to human and environmental health, and often select for mosquito resistance, making them ineffective and unsustainable [2]
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