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The sub-lethal effects of pyrethroid exposure on Anopheles gambiae s.l. life-history traits, behaviour, and the efficacy of insecticidal bednets

Lissenden, Natalie ORCID: (2020) The sub-lethal effects of pyrethroid exposure on Anopheles gambiae s.l. life-history traits, behaviour, and the efficacy of insecticidal bednets, Thesis (Doctoral), Liverpool School of Tropical Medicine.

N Lissenden - PhD Thesis.pdf - Accepted Version

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Malaria control progress in Africa has stalled. Though the reasons for this will be multifaceted, increasing and intense resistance to pyrethroids in Anopheles gambiae s.l. is almost certainly a contributing factor. Standard methods to monitor insecticide resistance and evaluate vector control tools primarily focus on the immediate and lethal effects on the mosquito. These methods disregard other important delayed and sub-lethal effects, despite their implications for malaria transmission. In response to growing concerns over the sustained effectiveness of current control tools, next-generation products are being developed and evaluated. These aim to target insecticide-resistant mosquitoes or mosquitoes that contribute to residual malaria transmission. Adaptations to current standard efficacy tests are needed to evaluate the novel modes of action of such products.
The effect of insecticide exposure on the longevity, reproductive output and blood-feeding behaviour of a wild highly pyrethroid-resistant Anopheles gambiae s.l. population was evaluated. Mosquitoes were exposed to a range of insecticides and insecticidal bednets using laboratory tests and semi-field experimental hut trials. Benchtop video tests were evaluated for their feasibly in measuring the effectiveness of standard and next-generation nets. Subsequently, these tests were used to investigate the behaviour of field-populations of An. gambiae s.l. at the bednet interface in response to a human host.
Following exposure to both pyrethroid-only and next-generation nets, evidence of sub-lethal impacts were limited or non-existent. The mosquitoes exposed to insecticidal nets did not suffer from reduced lifespan or altered reproductive output. Evidence of delayed mortality was only recorded when mosquitoes were exposed to extremely high levels of pyrethroids in WHO tube bioassays. Some mosquitoes were inhibited from blood-feeding in experimental hut trials, however, lab tests suggest this effect is absent by 8-hour post net-exposure. The efficacy of next-generation nets on the field population was dependant on the product. Brief contact with PermaNet 3.0 roof (pyrethroid + PBO) caused rapid knock-down and 100% mortality in all tests. Exposure to all other insecticidal nets, including Interceptor G2 (pyrethroid + chlorfenapyr), resulted in low 24-hour mortality in both lab and semi-field experiments. Following adaptations for the field, video tests were able to collect behavioural data on mosquito responses to insecticidal nets such as flying, resting, and probing behaviour. Responses were similar between untreated and pyrethroid-
only netting. Extreme reductions in activity were observed following exposure to PermaNet 3.0, and Interceptor G2 showed signs of repellence.
The results suggest community protection offered by first-generation LLINs is extremely low in this setting, however, pyrethroid-PBO nets appear to be effective at controlling the highly pyrethroid-resistant population. This work highlights the need for additional studies of sub-lethal effects in other field populations, with lower insecticide resistance levels or differing mechanisms, to establish if such measurements should be incorporated into the evaluation of novel vector control tools.

Item Type: Thesis (Doctoral)
Subjects: QX Parasitology > Insects. Other Parasites > QX 515 Anopheles
QX Parasitology > Insects. Other Parasites > QX 600 Insect control. Tick control
QX Parasitology > Insects. Other Parasites > QX 650 Insect vectors
WC Communicable Diseases > Tropical and Parasitic Diseases > WC 750 Malaria
WC Communicable Diseases > Tropical and Parasitic Diseases > WC 765 Prevention and control
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Anopheles gambiae populations from Burkina Faso show minimal delayed mortality after exposure to insecticide-treated nets.
Barrier bednets target malaria vectors and expand the range of usable insecticides.
Faculty: Department: Biological Sciences > Vector Biology Department
Depositing User: Lynn Roberts-Maloney
Date Deposited: 09 Apr 2020 11:06
Last Modified: 09 Jul 2020 01:02


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