Resistance to clothianidin reduces the efficacy of SumiShield® 50WG, a neonicotinoid formulation for indoor residual spraying, against Anopheles gambiae

Abstract

Chronic exposure of mosquito larvae to pesticide residues in agricultural areas is often associated with evolution of resistance to insecticides used for vector control. This presents a concern for the efficacy of clothianidin, an agricultural neonicotinoid qualified for Indoor Residual Spraying (IRS). Using standard bioassays, we tested if reduced susceptibility to clothianidin affects the efficacy of SumiShield® 50WG, one of the two newly approved formulations, which contains 50% clothianidin. We simultaneously monitored susceptibility to clothianidin and to SumiShield® 50WG, testing adults of Anopheles gambiae, An. coluzzii and Culex sp collected from urban, suburban and agricultural areas of Yaoundé. We found that the level of susceptibility to the active ingredient predicted the efficacy of SumiShield® 50WG. This formulation was very potent against populations that achieved 100% mortality within 72 h of exposure to a discriminating dose of clothianidin. By contrast, mortality leveled off at 75.4 ± 3.5% within 7 days of exposure to SumiShield® 50WG in An. gambiae adults collected from a farm where spraying of acetamiprid and imidacloprid is driving cross-resistance to clothianidin. These findings indicate that more potent formulations of clothianidin or different insecticides should be prioritized in areas where resistance is emerging.

Enhancing the efficacy of neonicotinoids against mosquitoes and overcoming resistance issues

“…Our study corroborated findings from earlier surveys indicating that clothianidin resistance is emerging in An. gambiae despite the fact this active ingredient remains an exotic insecticide in Cameroon 23,24 . By contrast, it has been reported that formulations of acetamiprid and imidacloprid are intensively used for crop protection in agricultural areas in Cameroon 19,23,27 .…”

“…In line with this prediction, a study revealed that An. gambiae larvae collected from Nkolondom retained high fitness when reared in water containing concentrations of neonicotinoids that were lethal to susceptible strains 24 The present study shows that neonicotinoid tolerance selected at larval stage induces cross-resistance to several active ingredients in female adult mosquitoes that are vectors of Plasmodium [23][24][25] . An.…”

“…A bioassay was performed to determine if the synergistic effect of the cytochrome P450 inhibitor, piperonyl butoxide (PBO) could restore neonicotinoid susceptibility. Mosquitoes that emerged from the same pool of larvae were first exposed to PBO at 4% in CDC bottles, for 1 h before being released into other bottles coated with the neonicotinoid insecticide as described in 23 . Mortality values obtained with or without prior exposure to the synergist were compared after 72 h of holding period.…”

“…coluzzii to acetamiprid, imidacloprid and thiamethoxam was determined from populations tested from 2020 to 2022. Susceptibility to clothianidin was estimated by pooling original data obtained from bioassays carried out between 2020 and 2022 with data presented in 23 , which originated from field collections conducted from 2019 to 2020. In total, 5532 female mosquitoes belonging to eleven populations were tested with bioassays from 2019 to 2022.…”

“…Neonicotinoids sprayed to protect crops from insect pests are highly water-soluble and are prone to leach in aquatic habitats that support Anopheles larvae in farms 20,21 . This unintentional exposure may contribute to the development of broad-spectrum neonicotinoid resistance [22][23][24][25] . Thus, in prospective areas where clothianidin formulations may be used, it is important to assess baseline susceptibility of vector populations to a wide range of neonicotinoid insecticides.…”