Repellent, irritant and toxic effects of 20 plant extracts on adults of the malaria vector Anopheles gambiae mosquito - PubMed (original) (raw)

Repellent, irritant and toxic effects of 20 plant extracts on adults of the malaria vector Anopheles gambiae mosquito

Emilie Deletre et al. PLoS One. 2013.

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.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1

Figure 1. Schematic drawing of a modified HITSS system, used to test spatial repellency.

The spatial repellency assay components are: 1, end cap; 2, metallic net; 3, treated chamber; 4, linking section (with a butterfly valve); 5, untreated chamber (adapted from Grieco et al. [18]).

Figure 2

Figure 2. Schematic drawing of a simplified WHO diagnostic test kit for measuring insecticide susceptibility/resistance status in adult malaria mosquitoes, used to demonstrate contact irritancy.

The contact irritancy assay components are: 1, end cap covered by net; 2, treated chamber; 3, linking section (guillotine valve); 4, untreated chamber (adapted from Grieco et al. [18]).

Figure 3

Figure 3. Response of four- to seven-day-old, non-blood-fed, sugar-fed, Kisumu strain of Anopheles gambiae females to the repellent effect of DEET, permethrin and 20 plant extracts at 3 concentrations (0.01, 0.1 and 1% of product in the solution on chromatographic papers): dendrogram determined by hierarchical ascendant classification and corrected proportion escaping using Abbott’s formula (confidence interval calculated with the Wald method) by treatment concentration.

  1. Pairwise comparison of proportion was done using Fisher’s test. Values in bold lettering were significantly different from the control with the Holm’s sequential Bonferroni correction method. 2) P-value of the generalized linear model of the interaction concentration-product (dose-dependency) on the mosquito repellency. The coefficient was compared to zero so only the P-value of positive coefficient is given.

Figure 4

Figure 4. Response of four- to seven-day-old, non-blood-fed, sugar-fed, Kisumu strain Anopheles gambiae females to the irritant effect of DEET, permethrin and 20 plant extracts at 3 concentrations (0.01, 0.1 and 1% of product in the solution on chromatographic papers): dendrogram determined by hierarchical ascendant classification and corrected proportion escaping using Abbott’s formula (confidence interval calculated with the Wald method) by treatment concentration.

  1. Pairwise comparison of proportion was done using Fisher’s test. Values in bold lettering were significantly different from the control with the Holm’s sequential Bonferroni correction method. 2) P-value of the generalized linear model of the interaction concentration-product (dose-dependency) on the mosquito irritancy. The coefficient was compared to zero so only the p-value of positive coefficient is given.

Figure 5

Figure 5. Responses of four- to seven-day old, non-blood-fed, sugar-fed, Kisumu strain of Anopheles gambiae females to the toxic effect of DEET, permethrin and 20 plant extracts at 3 concentrations (0.01, 0.1 and 1% of product in the solution on chromatographic papers): dendrogram determined by hierarchical ascendant classification and corrected mortality proportion using Abbott’s formula (confidence interval calculated with the Wald method) by treatment concentration.

  1. Pairwise comparison of proportion was done using Fisher’s test. Values in bold lettering were significantly different from the control with the Holm’s sequential Bonferroni correction method. 2) P-value of the generalized linear model of the interaction concentration-product (dose-dependency) on the mosquito mortality. The coefficient was compared to zero so only the p-value of positive coefficient is given.

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