We report the first finding of the knockdown Leu-Phe and Leu-Ser mutations associated with resistance to pyrethroids and DDT insecticides in the malaria mosquito Anopheles gambiae from Cameroon. The Leu-Phe mutation was found in both the M and S molecular forms of An. gambiae. Importantly, two specimens of the S molecular form were found to carry both mutations in a heterozygous state.

Summary: Objective  To explore temporal variation in insecticide susceptibility of Anopheles gambiae s.l. populations to the four chemical groups of insecticides used in public health and agriculture, in close match with the large‐scale cotton spraying programme implemented in the cotton‐growing area of North Cameroon.Methods  Mosquito larvae were collected in 2005 before (mid June), during (mid August) and at the end (early October) of the cotton spraying programme. Larvae were sampled in breeding sites located within the cotton fields in Gaschiga and Pitoa, and in Garoua, an urban cotton‐free area that served as a control. Insecticide susceptibility tests were carried out with 4% DDT (organochlorine), 0.4% chlorpyrifos methyl (organophosphate), 0.1% propoxur (carbamate), 0.05% deltamethrin and 0.75% permethrin (pyrethroids).Results  Throughout the survey, An. gambiae s.l. populations were completely susceptible to carbamate and organophosphate, whereas a significant decrease of susceptibility to organochlorine and pyrethroids was observed during spraying in cotton‐growing areas. Tolerance to these insecticides was associated with a slight increase of knockdown times compared to the reference strain. Among survivor mosquitoes, the East and West African Kdr mutations were detected only in two specimens of An. gambiae s.s. (n = 45) and not in Anopheles arabiensis (n = 150), suggesting metabolic‐based resistance mechanisms.Conclusions  Environmental disturbance due to the use of insecticides in agriculture may provide local mosquito populations with the enzymatic arsenal selecting tolerance to insecticides.

Increasing incidence of DDT and pyrethroid resistance in Anopheles mosquitoes is seen as a limiting factor for malaria vector control. The current study aimed at an in-depth characterization of An. gambiae s.l. resistance to insecticides in Cameroon, in order to guide malaria vector control interventions.

Vector control can contribute to the development of resistance to insecticides in malaria vectors. As the swamps and wetlands used for some agricultural activities constitute productive breeding sites for many mosquito species, agricultural pest control may increase the selection pressure for insecticide resistance in mosquitoes. Understanding the use of agrochemicals by farmers is important to plan and initiate effective integrated pest and vector management interventions. A knowledge–attitude–practice study, using questionnaires, was undertaken with 102 rice farmers in Tiassalé and 106 vegetable farmers in Dabou (South Côte d’Ivoire) in order to generate information on pesticide usage. In addition, insecticide susceptibility bioassays were conducted using adult mosquitoes obtained from larvae collected within farms, and the persistence of agricultural pesticides in the farming environment, including sediment and mosquito breeding site water, was investigated by HPLC. Herbicides and insecticides appeared to be the most frequently used pesticides for both crops. Amino phosphonates (mostly glyphosate) represented the most used herbicides (45 % for rice up to 89 % for vegetables). Pyrethroids appeared to be the most used insecticides (accounting for 90 % of all the insecticide use reported). Approximately 75 % of respondents had not been to school and do not understand product labels. Only about 45 % of farmers respect the recommended pesticide dosage and about 10–15 % of pesticides used for rice and vegetable, respectively, are not recommended for these crops. As per WHO criteria, the mosquito local populations from the two localities were resistant to three of the four insecticides tested, as mortalities were less than 35 % for deltamethrin, DDT and bendiocarb. Higher susceptibility was observed for malathion, although the population was considered resistant in Dabou (80 % mortality) and susceptible in Tiassalé (98 % mortality). With the exception of glyphosate, residues from each of six chemicals tested for were detected in each of the sites visited in the two localities. The study describes the use of insecticides and herbicides on crops and highlights the importance of considering agriculture practices when attempting to manage resistance in malaria vectors. Inter-sectoral collaboration between agriculture and public health is required to develop efficient integrated pest and vector management interventions.

The wetlands used for some agricultural activities constitute productive breeding sites for many mosquito species. Thus, the agricultural use of insecticide targeting other pests may select for insecticide resistance in malaria mosquitoes. The purpose of this study is to clarify some knowledge gaps on the role of agrochemicals in the development of insecticide resistance in malaria vectors is of utmost importance for vector control. Using the CDC bottle test and the log-probit analysis, we investigated for the first time the resistance levels of Anopheles coluzzii mosquitoes to neonicotinoids, insecticides used exclusively for crop protection in Côte d’Ivoire. The study was conducted in two agricultural regions (Tiassale and Gagnoa) and one non-agricultural region (Vitre) between June and August 2017 using clothianidin, acetamiprid and imidacloprid. Mosquito populations from Tiassale and Gagnoa (agricultural settings) were determined to be resistant to acetamiprid with mortality rates being < 85% at 24 h post-exposure. In Vitre (non-agricultural area) however, the mosquito population was susceptible to acetamiprid. In all three localities, mosquito populations were resistant to imidacloprid (mortality rates were 60% in Vitre, 37% in Tiassale, and 13% in Gagnoa) and completely susceptible to clothianidin (100% mortality). An. coluzzii represented 100% of mosquito collected in Gagnoa, 86% in Tiassale and 96% in Vitre. This study provides strong evidence that agricultural use of insecticides can cause insecticide resistance in malaria vector populations. Insecticide resistance driven by agrochemical usage should be considered when vector control strategies are developed.