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

Abstract

Abstract 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 now relatively well documented, little is known about the influence of the environment on the phenotypic expression of mosquito resistance to insecticides. In particular, the extent to which mosquito plant feeding affects the phenotypic expression of insecticide resistance remains unknown. To assess the effect of plant diet on the response of mosquitoes to insecticides, larvae from the predominant vector, Anopheles gambiae sensu latowere collected in southwestern Burkina Faso and reared until adulthood. Following emergence, adults were fed with one of four treatment (5% glucose solution, nectariferous flowers of Barleria lupulina, nectariferous flowers of Cascabela thevetia and a combination of both plants Barleria lupulina + Cascabela thevetia). WHO standard tube tests were performed with 0.05% and 0.5% deltamethrin. The measured end-point parameters were knockdown rate (KD) and the 24 h mosquito mortality. Following the bioassays, DNA was extracted from each mosquito individual for PCR identification of the siblings of the An. gambiae complex and determination of the kdr genotypic and allelic frequencies. Plant diet significantly influenced mosquito KD rate at both concentrations of deltamethrin. Following exposure to 0.05% deltamethrin, the Barleria lupulina diet induced a 2.5 fold-decrease in mosquito mortality compared to the 5% glucose treatment. The molecular data confirmed the predominance of An. gambiae (60% of the samples) over An. coluzzii and An. arabiensis. The kdr mutation L1014F displayed a high allelic frequency of 0.75 and, as expected, it was positively associated with increased resistance to deltamethrin. Plant diet, particularly B. lupulina, appears to increase 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 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