Conference abstract
Comparative study of the effect of solvents on the efficacy of neonicotinoid insecticides against malaria vector populations across Africa
Pan African Medical Journal - Conference Proceedings. 2023:18(121).03
Oct 2023.
doi: 10.11604/pamj-cp.2023.18.121.2230
Archived on: 03 Oct 2023
Contact the corresponding author
Keywords: Malaria vectors, resistance, Africa, neonicotinoids, solvents
Oral presentation
Comparative study of the effect of solvents on the efficacy of neonicotinoid insecticides against malaria vector populations across Africa
Tatiane Assatse1,&, Magellan Tchouakui2, Leon Mugenzi2, Benjamin D. Menze2, Daniel Nguiffo‑Nguete2, Williams Tchapga2, Jonathan Kayondo2, Francis Watsenga1, Emile Zola Manzambi2, Michael Osae2, Charles S. Wondji2
1University of Yaoundé I, Yaoundé, Cameroon, 2Centre for Research in Infectious Diseases, Yaoundé, Cameroon
&Corresponding author
Introduction: resistance monitoring of novel insecticides, recently recommended for public health use by WHO, requires a robust protocol to monitor the development of resistance in natural populations of mosquitoes. In this study, we comparatively used three different solvents to assess the susceptibility of malaria vectors to neonicotinoids across Africa. This study will help vector control intervention by assessing the susceptibility profile of malaria vectors to neonicotinoid insecticides before their deployment at a large scale.
Methods: we did a cross-sectional study across Africa. Mosquitoes were collected using an electric aspirator and the Dipping method from May to July 2021 from three agricultural settings in Cameroon, the Democratic Republic of Congo, Ghana, and Uganda. Using the CDC bottle test, we compared the effect of three different solvents (ethanol, acetone, acetone+MERO) on the efficacy of neonicotinoids against Anopheles gambiae s.l. In addition, TaqMan assays were used to genotype key pyrethroid-resistant markers in An. gambiae and to evaluate potential cross-resistance between pyrethroids and clothianidin. The data were analysed using R and the results were interpreted according to the WHO protocol.
Results: lower mortalities were observed for all populations when using absolute ethanol or acetone alone as solvent compared to acetone+MERO for which 100% mortality was observed. Synergist assays 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). The I114T-GSTe2 was in contrast significantly associated with a greater ability to survive clothianidin with a higher frequency of homozygote resistance among survivors than other genotypes (OR=2.10; P=0.013).
Conclusion: this study revealed a contrasted susceptibility pattern depending on the solvents with ethanol/acetone resulting in lower mortality, thus possibly overestimating resistance, whereas the addition of MERO consistently increased the efficacy of neonicotinoids in terms of percentage mortalities and time to final mortality. The addition of MERO could however prevent the early detection of resistance development. We, therefore, recommend monitoring susceptibility using acetone+MERO (8-10µg/ml for clothianidin) to capture the accurate resistance profile of the mosquito populations.
Comparative study of the effect of solvents on the efficacy of neonicotinoid insecticides against malaria vector populations across Africa
Tatiane Assatse1,&, Magellan Tchouakui2, Leon Mugenzi2, Benjamin D. Menze2, Daniel Nguiffo‑Nguete2, Williams Tchapga2, Jonathan Kayondo2, Francis Watsenga1, Emile Zola Manzambi2, Michael Osae2, Charles S. Wondji2
1University of Yaoundé I, Yaoundé, Cameroon, 2Centre for Research in Infectious Diseases, Yaoundé, Cameroon
&Corresponding author
Introduction: resistance monitoring of novel insecticides, recently recommended for public health use by WHO, requires a robust protocol to monitor the development of resistance in natural populations of mosquitoes. In this study, we comparatively used three different solvents to assess the susceptibility of malaria vectors to neonicotinoids across Africa. This study will help vector control intervention by assessing the susceptibility profile of malaria vectors to neonicotinoid insecticides before their deployment at a large scale.
Methods: we did a cross-sectional study across Africa. Mosquitoes were collected using an electric aspirator and the Dipping method from May to July 2021 from three agricultural settings in Cameroon, the Democratic Republic of Congo, Ghana, and Uganda. Using the CDC bottle test, we compared the effect of three different solvents (ethanol, acetone, acetone+MERO) on the efficacy of neonicotinoids against Anopheles gambiae s.l. In addition, TaqMan assays were used to genotype key pyrethroid-resistant markers in An. gambiae and to evaluate potential cross-resistance between pyrethroids and clothianidin. The data were analysed using R and the results were interpreted according to the WHO protocol.
Results: lower mortalities were observed for all populations when using absolute ethanol or acetone alone as solvent compared to acetone+MERO for which 100% mortality was observed. Synergist assays 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). The I114T-GSTe2 was in contrast significantly associated with a greater ability to survive clothianidin with a higher frequency of homozygote resistance among survivors than other genotypes (OR=2.10; P=0.013).
Conclusion: this study revealed a contrasted susceptibility pattern depending on the solvents with ethanol/acetone resulting in lower mortality, thus possibly overestimating resistance, whereas the addition of MERO consistently increased the efficacy of neonicotinoids in terms of percentage mortalities and time to final mortality. The addition of MERO could however prevent the early detection of resistance development. We, therefore, recommend monitoring susceptibility using acetone+MERO (8-10µg/ml for clothianidin) to capture the accurate resistance profile of the mosquito populations.
