Abstract
BackgroundLaboratory and field studies showed that repellent, irritant and toxic actions of common public health insecticides reduce human-vector contact and thereby interrupt disease transmission. One of the more effective strategies to reduce disease risk involves the use of long-lasting treated bednets. However, development of insecticide resistance in mosquito populations makes it imperative to find alternatives to these insecticides. Our previous study identified four essential oils as alternatives to pyrethroids: Thymus vulgaris, Cymbopogon winterianus, Cuminum cyminum, Cinnamomum zeylanicum. The objectives of this study were to identify active compounds of these essential oils, to characterize their biological activity, and to examine their potential as a treatment for bednets.MethodsWe evaluated the electrophysiological, behavioural (repellency, irritancy) and toxic effects of the major compounds of these oils against Anopheles gambiae strain ‘Kisumu’.ResultsAldehydes elicited the strongest responses and monoterpenes the weakest responses in electroantennogram (EAG) trials. However, EAG responses did not correlate consistently with results of behavioral assays. In behavioral and toxicity studies, several of the single compounds did exhibit repellency, irritancy or toxicity in An. gambiae; however, the activity of essential oils did not always correlate with activity expected from the major components. On the contrary, the biological activity of essential oils appeared complex, suggesting interactions between individual compounds and the insect under study. Data also indicated that the three effects appeared independent, suggesting that repellency mechanism(s) may differ from mechanisms of irritancy and toxicity.ConclusionsBased on the bioassays reported here, some of the compounds merit consideration as alternative bednet treatments.
Highlights
Laboratory and field studies showed that repellent, irritant and toxic actions of common public health insecticides reduce human-vector contact and thereby interrupt disease transmission
In previous studies we evaluated promising essential oils from four plants: Thymus vulgaris, Cymbopogon winterianus, Cuminum cyminum, Cinnamomum zeylanicum for their repellent, irritant and toxic effect [10]
The following products exhibited the same repellency as the essential oil from which they come from: carvacrol, citronellal, geraniol, citronellol, cuminaldehyde, γ-terpinene
Summary
Laboratory and field studies showed that repellent, irritant and toxic actions of common public health insecticides reduce human-vector contact and thereby interrupt disease transmission. Some of the better known repellents are citronellal, myrcene, geraniol, citral, limonene, pinenes, citronellol, eugenol, and linalool [6] These natural compounds are biodegradable and environmentally friendly and are well accepted by people who want to avoid synthetic chemicals [7]. With multiple bioactive compounds present in an essential oil, the oil can affect multiple targets at the same time; neither resistance nor adaptation to these products has been yet documented [9]. Despite their wide use, it is important to improve upon our knowledge of bioactive compound(s) to better understand their full potential as repellents and/or insecticides
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