Evaluation of toxicity of clothianidin (neonicotinoid) and chlorfenapyr (pyrrole) insecticides and cross-resistance to other public health insecticides in Anopheles arabiensis from Ethiopia

Abstract

Background Insecticide-based interventions play an integral role in malaria vector control. However, the continued spread of insecticide resistance threatens to undermine progress made thus far and may ultimately lead to operational failure of current control measures. Clothianidin and chlorfenapyr both have unique modes of action and have expanded the number of insecticide classes available to vector control programmes. Prior to field use, it is imperative to establish their toxicity against local mosquito populations and evaluate potential cross-resistance with other chemicals used contemporarily or historically. The aim of this study was to determine the diagnostic doses of clothianidin and chlorfenapyr and their efficacies against Anopheles arabiensis , the predominant Ethiopian malaria vector species. Methods A range of doses of clothianidin and chlorfenapyr were tested, using modified WHO susceptibility tests and CDC bottle bioassays, respectively, against an Ethiopian susceptible laboratory strain and a wild population of An. arabiensis collected from Oromia Region, Ethiopia. Cross-resistance to other public health insecticides: carbamates (bendiocarb and propoxur), organophosphate (malathion) and pyrethroids (deltamethrin and permethrin), was assessed in the same mosquito populations using CDC bottle bioassays. Results Complete mosquito mortality was observed with the laboratory strain using the recommended diagnostic doses for clothianidin (2%/filter paper) and chlorfenapyr (100 µg/bottle). The field population was resistant to malathion (83% mortality), capable of surviving 2×, 5× and 10× the diagnostic dose of both deltamethrin and permethrin, but susceptible to bendiocarb and propoxur. The field population of An. arabiensis was significantly more susceptible to clothianidin, reaching 100% mortality by day 2 compared to the laboratory strain (100% mortality by day 3). In contrast, the wild population was less susceptible to chlorfenapyr, with the highest mortality of 99% at 72 h using 200 µg/bottle compared to the laboratory colony, which reached complete mortality at 50 µg/bottle by 24 h. Conclusions The putative diagnostic doses of clothianidin and chlorfenapyr are appropriate for monitoring resistance in An. arabiensis from Ethiopia. The unique modes of action and an absence of cross-resistance render clothianidin and chlorfenapyr potential candidates for inclusion in the National Malaria Control Programme vector control efforts, particularly in areas with high pre-existing or emergent resistance to other insecticide classes.

High level of resistance in Anopheles arabiensis mosquito to pyrethroid insecticides from low malaria transmission zone of Moroto district, Karamoja region, Uganda: Implication for malaria vector control

“…These insecticide resistances could as well have important implications for the epidemiology of malaria as well as malaria vector control in the low malaria transmission zones of Karamoja areas. Although pyrethoids are currently used in all LLINS as recommended by the World Health Organization, there are also used in combination with either synergists (PBO) [55] or other active ingredient like clothianidin, chlorfenapyr in Interceptor G2 [7,8]. However, pyrethroid resistance of malaria vectors is still widespread in Africa as well as other classes of insecticides [23,37,56].…”

“…WHO recommend organochlorines, organophosphates, pyrethroids and carbamates for control of malaria vectors, among which pyrethroids are the only WHO prequali ed insecticides for LLINs, and are also extensively used for IRS due to their low cost, human safety and long duration of residual action [4]. However, there are other novel pyrolle and neonicotinoid insecticide compounds like pyrolle chlorfenapyr and neonicotinoid clothianidin that are used in LLINS and IRS in combination with pyrethroids and all have different mode of actions [7][8][9] The LLINs and IRS are widely promoted and implemented as public health intervention tool for malaria control in most malaria-endemic countries including Uganda [10]. In most of Uganda, LLINs is selectively implemented in the different regions, with an average operational coverage of over 95% [11].…”

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

“…We used a diagnostic dose of 2% w/v clothianidin (13.2 mg active ingredient per paper) based on guidance from Sumitomo Corporation and the US President's Malaria Initiative. This dose has been successfully used to test the toxicity of clothianidin towards wild anopheline populations from Sub-Saharan Africa [18,37]. We prepared a stock solution by diluting 264 mg SumiShield 50WG in 20 ml distilled water.…”

“…Assessing clothianidin susceptibility in Anopheles mosquitoes using conventional bioassays has been met with some technical challenges so far [18,22,35,37,44]. Clothianidin is difficult to solubilize in solvents commonly used in bioassays, which has made the design of standard protocols more laborious than usual [18,35,37]. In addition, because this active ingredient acts slowly, resistance profiles are revealed via laboratory bioassays only if exposed populations are rigorously monitored during a long holding period, which can last seven days or more.…”

“…In addition, because this active ingredient acts slowly, resistance profiles are revealed via laboratory bioassays only if exposed populations are rigorously monitored during a long holding period, which can last seven days or more. Despite these difficulties, the susceptibility of wild Anopheles populations from several African countries has been successfully evaluated using the recommended diagnostic doses of clothianidin [18,22,35,37 arabiensis [18,22,35,37]. Resistance to clothianidin was not detected among populations from 16 countries where 100% mortality was reached on average 72 h following exposure in all populations tested either with WHO tube tests [18,37] or with CDC bottle assays [22,35].…”