High larvicidal efficacy of yeast-encapsulated orange oil against Aedes aegypti strains from Brazil

Abstract

Background Botanical substances such as essential oils (EOs) have demonstrated insecticidal properties and are a valid option for vector control. However, free EOs are unreliable as mosquito larvicides due their easy degradation by environmental exposure to ultraviolet light and higher temperatures. Here, we assessed the efficacy of a mosquito larvicide based on orange oil in a yeast-based delivery system against Aedes aegypti strains with different resistance status towards chemical neurotoxic insecticides. This larvicide preparation was physicochemically characterized in a previous report. Methods Larvae of four Ae. aegypti strains from different regions of Brazil and different resistance profiles for deltamethrin (pyrethroid) and temephos (organophosphate) were tested against yeast-encapsulated orange oil (YEOO) in laboratory conditions for measurement of LC50 and LC90 values. The same assays were performed with the Belo Horizonte strain under environmental conditions (natural light and temperature). The resistance profiles of these strains were compared to the Rockefeller reference strain in all conditions. Results YEOO was found to be a highly active larvicide (LC50 < 50 mg/L) against all Ae. aegypti strains tested in both laboratory conditions (LC50 = 8.1–24.7 mg/L) and environmental conditions with natural light and temperature fluctuation (LC50 = 20.0–49.9 mg/L). Moreover, all strains were considered susceptible (RR < 5) to YEOO, considering resistance ratios calculated based on the Rockefeller strain. The resistance ratios were only higher than 2.5 for LC90–95 of Belo Horizonte in the laboratory, probably due the higher heterogeneity associated with older egg papers (> 5 months). Conclusion YEOO demonstrates high larvicidal activity against Ae. aegypti strains with resistant phenotypes for deltamethrin (PY) and temephos (OP). This larvicidal activity suggests the potential for the development of YEOO as an alternative intervention to synthetic insecticides in integrated vector management programs, for populations with resistance to commonly used insecticides. Graphic Abstract

The impact of yeast-encapsulated orange oil in Aedes aegypti oviposition

“…YEOO is a novel larvicide with high efficiency against Ae . aegypti [ 9 , 10 ], and it is vital to understand its alternative impacts on mosquito vectors, particularly in oviposition behaviour. Substances with attractive/stimulant properties for oviposition can potentially improve trapping systems for gravid females by improving egg-laying in the traps while preventing it in other water reservoirs.…”

“…In previous studies, yeast-encapsulated orange oil (YEOO) was shown as a novel larvicide, with high efficiency (LC 50 <50 mg/L) against Ae . aegypti in small-scale laboratory trials [ 9 , 10 ].…”

Larvicidal properties of terpenoid-based nanoemulsions against the dengue vector Aedes aegypti L. and their potential toxicity against non-target organism

“…Other strategies than nanoemulsions were used for the stabilization of essential oils, for example using yeast for the encapsulation of orange oil, and this strategy showed to be highly active (LD 50 < 50 mg.L -1 ) against Ae . aegypti [ 59 , 60 ].These differences in the chemical composition of the essential oils and the type of the stabilization method can affect the interaction of the terpenes or essential one’s with mosquitoes and explain the different outcomes observed in our study compared to previous one’s.…”

Óleos essenciais e extratos vegetais como ferramentas alternativas ao controle químico de larvas de Aedes spp, Anopheles spp e Culex spp

“…Entretanto, o seu uso destinado ao controle de insetos vetores de patógenos aos humanos restringe-se ao efeito repelente exibido por um número limitado de substâncias 49 . A atividade larvicida demonstrada por uma grande variedade de extratos vegetais e óleos essenciais representa uma alternativa ao tradicional controle químico baseado em inseticidas sintéticos, utilizado nos programas de manejo integrado de vetores 50 . Deve-se, portanto, estimular as pesquisas centradas na prospecção desses produtos, estabelecendo-se protocolospadrão que levem em consideração aspectos relacionados às espécies vegetais investigadas, como a coleta, a extração e a definição dos constituintes químicos, bem como dos insetosalvo, como a procedência dos espécimes e o estágio do desenvolvimento 51 .…”