Dataset Information

Insecticide-induced leg loss does not eliminate biting and reproduction in Anopheles gambiae mosquitoes.

ABSTRACT: Recent successes in malaria control have been largely attributable to the deployment of insecticide-based vector control tools such as bed nets and indoor residual spraying. Pyrethroid-treated bed nets are acutely neurotoxic to mosquitoes, inducing symptoms such as loss of coordination, paralysis, and violent spasms. One result of pyrethroid exposure often seen in laboratory tests is mosquito leg loss, a condition that has thus far been assumed to equate to mortality, as females are not expected to blood feed. However, whilst limb loss is unlikely to be adaptive, females with missing limbs may play a role in the propagation of both their species and pathogens. To test the hypothesis that leg loss inhibits mosquitoes from biting and reproducing, mosquitoes with one, two, or six legs were evaluated for their success in feeding upon a human. These experiments demonstrated that insecticide-induced leg loss had no significant effect upon blood feeding or egg laying success. We conclude that studies of pyrethroid efficacy should not discount mosquitoes that survive insecticide exposure with fewer than six legs, as they may still be capable of biting humans, reproducing, and contributing to malaria transmission.

SUBMITTER: Isaacs AT

PROVIDER: S-EPMC5404223 | biostudies-literature | 2017 Apr

REPOSITORIES: biostudies-literature

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Insecticide-induced leg loss does not eliminate biting and reproduction in Anopheles gambiae mosquitoes.

Isaacs Alison T AT Lynd Amy A Donnelly Martin J MJ

Scientific reports 20170425

Recent successes in malaria control have been largely attributable to the deployment of insecticide-based vector control tools such as bed nets and indoor residual spraying. Pyrethroid-treated bed nets are acutely neurotoxic to mosquitoes, inducing symptoms such as loss of coordination, paralysis, and violent spasms. One result of pyrethroid exposure often seen in laboratory tests is mosquito leg loss, a condition that has thus far been assumed to equate to mortality, as females are not expected ...[more]

PMID: 28440300

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Project description:BackgroundLong-lasting insecticidal nets are an effective tool in reducing malaria transmission. However, with increasing insecticide resistance little is known about how physiologically resistant malaria vectors behave around a human-occupied bed net, despite their importance in malaria transmission. We used the Mbita bednet trap to assess the host-seeking behavior of insecticide-resistant Anopheles gambiae mosquitoes under semi-field conditions. The trap incorporates a mosquito netting panel which acts as a mechanical barrier that prevents host-seeking mosquitoes from reaching the human host baiting the trap.MethodsSusceptible and pyrethroid-resistant colonies of female Anopheles gambiae mosquitoes aged 3-5 days old were used in this study. The laboratory-bred mosquitoes were color-marked with fluorescent powders and released inside a semi-field environment where a human subject slept inside a bednet trap erected in a traditional African hut. The netting panel inside the trap was either untreated (control) or deltamethrin-impregnated. The mosquitoes were released outside the hut. Only female mosquitoes were used. A window exit trap was installed on the hut to catch mosquitoes exiting the hut. A prokopack aspirator was used to collect indoor and outdoor resting mosquitoes. In addition, clay pots were placed outside the hut to collect outdoor resting mosquitoes. The F1 progeny of wild-caught mosquitoes were also used in these experiments.ResultsThe mean number of resistant mosquitoes trapped in the deltamethrin-impregnated bed net trap was higher (mean = 50.21± 3.7) compared to susceptible counterparts (mean + 22.4 ± 1.31) (OR = 1.445; P<0.001). More susceptible mosquitoes were trapped in an untreated (mean = 51.9 ± 3.6) compared to a deltamethrin-treated bed net trap (mean = 22.4 ± 1.3) (OR = 2.65; P<0.001). Resistant mosquitoes were less likely to exit the house when a treated bed net was present compared to the susceptible mosquitoes. The number of susceptible mosquitoes caught resting outdoors (mean + 28.6 ± 2.22) when a treated bed net was hanged was higher than when untreated bednet was present inside the hut (mean = 4.6 ± 0.74). The susceptible females were 2.3 times more likely to stay outdoors away from the treated bed net (OR = 2.25; 95% CI = [1.7-2.9]; P<0.001).ConclusionThe results show that deltamethrin-treatment of netting panels inside the bednet trap did not alter the host-seeking behavior of insecticide-resistant female An. gambiae mosquitoes. On the contrary, susceptible females exited the hut and remained outdoors when a treated net was used. However, further investigations of the behavior of resistant mosquitoes under natural conditions should be undertaken to confirm these observations and improve the current intervention which are threatened by insecticide resistance and altered vector behavior.

Project description:BackgroundThe emergence of pyrethroid resistance in Anopheles gambiae has become a serious concern to the future success of malaria control. In Benin, the National Malaria Control Programme has recently planned to scaling up long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) for malaria prevention. It is, therefore, crucial to monitor the level and type of insecticide resistance in An. gambiae, particularly in southern Benin where reduced efficacy of insecticide-treated nets (ITNs) and IRS has previously been reported.MethodsThe protocol was based on mosquito collection during both dry and rainy seasons across forty districts selected in southern Benin. Bioassay were performed on adults collected from the field to assess the susceptibility of malaria vectors to insecticide-impregnated papers (permethrin 0.75%, delthamethrin 0.05%, DDT 4%, and bendiocarb 0.1%) following WHOPES guidelines. The species within An. gambiae complex, molecular form and presence of kdr and ace-1 mutations were determined by PCR.ResultsStrong resistance to permethrin and DDT was found in An. gambiae populations from southern Benin, except in Aglangandan where mosquitoes were fully susceptible (mortality 100%) to all insecticides tested. PCR showed the presence of two sub-species of An. gambiae, namely An. gambiae s.s, and Anopheles melas, with a predominance for An. gambiae s.s (98%). The molecular M form of An. gambiae was predominant in southern Benin (97%). The kdr mutation was detected in all districts at various frequency (1% to 95%) whereas the Ace-1 mutation was found at a very low frequency (<or= 5%).ConclusionThis study showed a widespread resistance to permethrin in An. gambiae populations from southern Benin, with a significant increase of kdr frequency compared to what was observed previously in Benin. The low frequency of Ace-1 recorded in all populations is encouraging for the use of bendiocarb as an alternative insecticide to pyrethroids for IRS in Benin.

Dataset Information

Insecticide-induced leg loss does not eliminate biting and reproduction in Anopheles gambiae mosquitoes.

Publications

Insecticide-induced leg loss does not eliminate biting and reproduction in Anopheles gambiae mosquitoes.

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