Is Anopheles gambiae (sensu stricto), the principal malaria vector in Africa prone to resistance development against new insecticides? Outcomes from laboratory exposure of An. gambiae (s.s.) to sub-lethal concentrations of chlorfenapyr and clothianidin

Abstract

Indiscriminate use of pesticides in the public health and agriculture sectors has contributed to the development of resistance in malaria vectors following exposure to sub-lethal concentrations. To preserve the efficacy of vector control tools and prevent resistance from spreading, early resistance detection is urgently needed to inform management strategies. The introduction of new insecticides for controlling malaria vectors such as clothianidin and chlorfenapyr requires research to identify early markers of resistance which could be used in routine surveillance. This study investigated phenotypic resistance of Anopheles gambiae (sensu stricto) Muleba-Kis strain using both WHO bottle and tube assays following chlorfenapyr, clothianidin, and alpha-cypermethrin selection against larvae and adults under laboratory conditions. High mortality rates were recorded for both chlorfenapyr-selected mosquitoes that were consistently maintained for 10 generations (24-h mortality of 92-100% and 72-h mortality of 98-100% for selected larvae; and 24-h mortality of 95-100% and 72-h mortality of 98-100% for selected adults). Selection with clothianidin at larval and adult stages showed a wide range of mortality (18-91%) compared to unselected progeny where mortality was approximately 99%. On the contrary, mosquitoes selected with alpha-cypermethrin from the adult selection maintained low mortality (28% at Generation 2 and 23% at Generation 4) against discrimination concentration compared to unselected progeny where average mortality was 51%. The observed resistance in the clothianidin-selected mosquitoes needs further investigation to determine the underlying resistance mechanism against this insecticide class. Additionally, further investigation is recommended to develop molecular markers for observed clothianidin phenotypic resistance.

Keywords: Insecticide resistance; Malaria; Mosquito generation; Selection; Vector.

Graphical abstract

Fig. 1

The mortality of An.gambiae (s.s.) Muleba-Kis strain from chlorfenapyr larvae selection against 100 μg/bottle chlorfenapyr. Bars indicate percent mortality for sample sizes of 80 mosquitoes for Generations 0 and 5, and of 100 mosquitoes for Generations 7 and 10. Error bars represent 95% confidence intervals.

Fig. 2

The mortality of An.gambiae (s.s.) Muleba-Kis strain from chlorfenapyr adult selection against 100 μg/bottle chlorfenapyr. Bars indicate percent mortality for sample sizes of 80 mosquitoes for Generations 0 and 5, 81 mosquitoes for Generation 7, and 104 mosquitoes for Generation 10. Error bars represent 95% confidence intervals.

Fig. 3

The mortality of An.gambiae (s.s.) Muleba-Kis strain from clothianidin larvae selection against 90 μg/bottle clothianidin. Bars indicate percent mortality for sample sizes of 80 mosquitoes for Generations 0 and 5, 40 mosquitoes for Generation 7, and 100 mosquitoes for Generation 10. Error bars represent 95% confidence intervals.

Fig. 4

The mortality of An.gambiae (s.s.) Muleba-Kis strain from clothianidin adult selection against 90 μg/bottle clothianidin. Bars indicate percent mortality for sample sizes of 80 mosquitoes for Generation 0, 40 mosquitoes for Generation 5, 101 mosquitoes for Generation 7, and 75 mosquitoes for Generation 10. Error bars represent 95% confidence intervals.

Fig. 5

The mortality of An.gambiae (s.s.) Muleba-Kis strain from alpha-cypermethrin adult selection against 12.5 μg/bottle alpha-cypermethrin. Bars indicate percent mortality for sample sizes of 100 mosquitoes for Generation 0 and 80 mosquitoes for Generations 2 and 4. Error bars represent 95% confidence intervals.