Repellent, Irritant and Toxic Effects of 20 Plant Extracts on Adults of the Malaria Vector Anopheles gambiae Mosquito

Abstract

Pyrethroid insecticides induce an excito-repellent effect that reduces contact between humans and mosquitoes. Insecticide use is expected to lower the risk of pathogen transmission, particularly when impregnated on long-lasting treated bednets. When applied at low doses, pyrethroids have a toxic effect, however the development of pyrethroid resistance in several mosquito species may jeopardize these beneficial effects. The need to find additional compounds, either to kill disease-carrying mosquitoes or to prevent mosquito contact with humans, therefore arises. In laboratory conditions, the effects (i.e., repellent, irritant and toxic) of 20 plant extracts, mainly essential oils, were assessed on adults of Anopheles gambiae, a primary vector of malaria. Their effects were compared to those of DEET and permethrin, used as positive controls. Most plant extracts had irritant, repellent and/or toxic effects on An. gambiae adults. The most promising extracts, i.e. those combining the three types of effects, were from Cymbopogon winterianus, Cinnamomum zeylanicum and Thymus vulgaris. The irritant, repellent and toxic effects occurred apparently independently of each other, and the behavioural response of adult An. gambiae was significantly influenced by the concentration of the plant extracts. Mechanisms underlying repellency might, therefore, differ from those underlying irritancy and toxicity. The utility of the efficient plant extracts for vector control as an alternative to pyrethroids may thus be envisaged.

Locomotory and physiological responses induced by clove and cinnamon essential oils in the maize weevil Sitophilus zeamais

“…These compounds repel or induce avoidance behavior in insects [17,18,[66][67][68][69]. Here, all the S. zeamais populations significantly avoided surfaces that were treated with these oils, and differential locomotory strategies were observed between the phosphine-and pyrethroid-susceptible (i.e.…”

Learning and Memory in Disease Vector Insects

“…Also, the effect of DEET by contact [48] could induce aversive learning, which, to our knowledge, has yet to be documented in vector insects. Such aversive learning may counteract the decreased repellency of DEET observed after pre-exposure to volatiles.…”

Green tea proanthocyanidins cause impairment of hormone-regulated larval development and reproductive fitness via repression of juvenile hormone acid methyltransferase, insulin-like peptide and cytochrome P450 genes in Anopheles gambiae sensu stricto

“…As a result, evaluations of diverse plant compounds have shown direct toxicities and growth inhibitory properties [43–45] while others confer repellent properties [46]. Despite the rigorous research on bioactive phytocompounds, information regarding their molecular mechanisms of action, which could lead to production of selective, target-specific and resistance-resilient insecticides against malaria-transmitting mosquitoes, is still lacking for most of these compounds.…”