Natural plant diet impacts phenotypic expression of pyrethroid resistance in Anopheles mosquitoes

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Résumé

Success in reducing malaria transmission through vector control is threatened by insecticide resistance
in mosquitoes. Although the proximal molecular mechanisms and genetic determinants involved are
well documented, little is known about the influence of the environment on mosquito resistance to
insecticides. The aim of this study was to assess the effect of plant sugar feeding on the response of
Anopheles gambiae sensu lato to insecticides. Adults were fed with one of four treatments, namely
a 5% glucose control solution, nectariferous flowers of Barleria lupulina, of Cascabela thevetia and
a combination of both B. lupulina + C. thevetia. WHO tube tests were performed with 0.05% and
0.5% deltamethrin, and knockdown rate (KD) and the 24 h mosquito mortality were measured. Plant
diet significantly influenced mosquito KD rate at both concentrations of deltamethrin. Following
exposure to 0.05% deltamethrin, the B. lupulina diet induced a 2.5 fold‑increase in mosquito
mortality compared to 5% glucose. Species molecular identification confirmed the predominance
of An. gambiae (60% of the samples) over An. coluzzii and An. arabiensis in our study area. The
kdr mutation L1014F displayed an allelic frequency of 0.75 and was positively associated with
increased phenotypic resistance to deltamethrin. Plant diet, particularly B. lupulina, increased the
susceptibility of mosquitoes to insecticides. The finding that B. lupulina‑fed control individuals (i.e.
not exposed to deltamethrin) also displayed increased 24 h mortality suggests that plant‑mediated
effects may be driven by a direct effect of plant diet on mosquito survival rather than indirect effects
through interference with insecticide‑resistance mechanisms. Thus, some plant species may weaken
mosquitoes, making them less vigorous and more vulnerable to the insecticide. There is a need for
further investigation, using a wider range of plant species and insecticides, in combination with other
relevant environmental factors, to better understand the expression and evolution of insecticide
resistance

Mots-clés

Plant diets, plant sugar feeding, phenotypic resistance, vector control