Background:New insecticides with a novel mode of action such as neonicotinoids have recently been recommended for public health by WHO.Resistance monitoring of such novel insecticides requires a robust protocol to mon...Background:New insecticides with a novel mode of action such as neonicotinoids have recently been recommended for public health by WHO.Resistance monitoring of such novel insecticides requires a robust protocol to monitor the development of resistance in natural populations.In this study,we comparatively used three different solvents to assess the susceptibility of malaria vectors to neonicotinoids across Africa.Methods:Mosquitoes were collected from May to July 2021 from three agricultural settings in Cameroon(Njombe-Penja,Nkolondom,and Mangoum),the Democratic Republic of Congo(Ndjili-Brasserie),Ghana(Obuasi),and Uganda(Mayuge).Using the CDC bottle test,we compared the effect of three different solvents(ethanol,acetone,MERO)on the efficacy of neonicotinoids againstAnopheles gambiae s.l.In addition,TaqMan assays were used to genotype key pyrethroid-resistant markers inAn.gambiae and odds ratio based on Fisher exact test were used to evaluate potential cross-resistance between pyrethroids and clothianidin.Results:Lower mortality was observed when using absolute ethanol or acetone alone as solvent for clothianidin(11.4-51.9% mortality in Nkolondom,31.7-48.2% in Mangoum,34.6-56.1% in Mayuge,39.4-45.6% in Obuasi,83.7-89.3% in Congo and 71.1-95.9% in Njombe pendja)compared to acetone+MERO for which 100% mortality were observed for all the populations.Similar observations were done for imidacloprid and acetamiprid.Synergist assays(PBO,DEM and DEF)with clothianidin revealed a significant increase of mortality suggesting that metabolic resistance mechanisms are contributing to the reduced susceptibility.A negative association was observed between the L1014F-kdr mutation and clothianidin resistance with a greater frequency of homozygote resistant mosquitoes among the dead than among survivors(OR=0.5;P=0.02).However,the I114T-GSTe2 was in contrast significantly associated with a greater ability to survive clothianidin with a higher frequency of homozygote resistant among survivors than other genotypes(OR=2.10;P=0.013).Conclusions:This study revealed a contrasted susceptibility pattern depending on the solvents with ethanol/acetone resulting to lower mortality,thus possibly overestimating resistance,whereas the MERO consistently showed a greater efficacy of neonicotinoids but it could prevent to detect early resistance development.Therefore,we recommend monitoring the susceptibility using both acetone alone and acetone+MERO(4μg/ml for clothianidin)to capture the accurate resistance profile of the mosquito populations.展开更多
文摘Background:New insecticides with a novel mode of action such as neonicotinoids have recently been recommended for public health by WHO.Resistance monitoring of such novel insecticides requires a robust protocol to monitor the development of resistance in natural populations.In this study,we comparatively used three different solvents to assess the susceptibility of malaria vectors to neonicotinoids across Africa.Methods:Mosquitoes were collected from May to July 2021 from three agricultural settings in Cameroon(Njombe-Penja,Nkolondom,and Mangoum),the Democratic Republic of Congo(Ndjili-Brasserie),Ghana(Obuasi),and Uganda(Mayuge).Using the CDC bottle test,we compared the effect of three different solvents(ethanol,acetone,MERO)on the efficacy of neonicotinoids againstAnopheles gambiae s.l.In addition,TaqMan assays were used to genotype key pyrethroid-resistant markers inAn.gambiae and odds ratio based on Fisher exact test were used to evaluate potential cross-resistance between pyrethroids and clothianidin.Results:Lower mortality was observed when using absolute ethanol or acetone alone as solvent for clothianidin(11.4-51.9% mortality in Nkolondom,31.7-48.2% in Mangoum,34.6-56.1% in Mayuge,39.4-45.6% in Obuasi,83.7-89.3% in Congo and 71.1-95.9% in Njombe pendja)compared to acetone+MERO for which 100% mortality were observed for all the populations.Similar observations were done for imidacloprid and acetamiprid.Synergist assays(PBO,DEM and DEF)with clothianidin revealed a significant increase of mortality suggesting that metabolic resistance mechanisms are contributing to the reduced susceptibility.A negative association was observed between the L1014F-kdr mutation and clothianidin resistance with a greater frequency of homozygote resistant mosquitoes among the dead than among survivors(OR=0.5;P=0.02).However,the I114T-GSTe2 was in contrast significantly associated with a greater ability to survive clothianidin with a higher frequency of homozygote resistant among survivors than other genotypes(OR=2.10;P=0.013).Conclusions:This study revealed a contrasted susceptibility pattern depending on the solvents with ethanol/acetone resulting to lower mortality,thus possibly overestimating resistance,whereas the MERO consistently showed a greater efficacy of neonicotinoids but it could prevent to detect early resistance development.Therefore,we recommend monitoring the susceptibility using both acetone alone and acetone+MERO(4μg/ml for clothianidin)to capture the accurate resistance profile of the mosquito populations.
