Semi-field evaluation of the space spray efficacy of Fludora Co-Max EW against wild insecticide-resistant Aedes aegypti and Culex quinquefasciatus mosquito populations from Abidjan, Côte d’Ivoire
Authors: Zahouli Julien Z. B. , Dibo Jean-Denis , Diakaridia Fofana , Yao Laurence , Souza Sarah D. , Horstmann Sebastian , Koudou Benjamin G. 
Published: May 2022

Background

Space spraying of insecticides is still an important mean of controlling Aedes and Culex mosquitoes and arboviral diseases. This study evaluated the space spray efficacy of Fludora Co-Max EW (a combination of flupyradifurone and transfluthrin, with Film Forming Aqueous Spray Technology (FFAST)) against wild, insecticide-resistant Aedes aegypti and Culex quinquefasciatus populations from Abidjan, Côte d’Ivoire, against K-Othrine EC (deltamethrin-only product), through small-scale field trials.

Methodology

Wild Ae. aegypti and Cx. quinquefasciatus mosquito larvae were collected in Abidjan, Côte d’Ivoire from August to December 2020. Mosquito larvae were reared until adult stage. Emerged adult females were tested against Fludora Co-Max EW and K-Othrine EC using ultra-low volume cold fogging (ULV) and thermal fogging (TF) both outdoors and indoors in Agboville, Côte d’Ivoire. Cages containing 20 mosquitoes each were placed at 10, 25, 50, 75 and 100 m from the spraying line for outdoor spraying, and at ceiling, mid-height and floor levels for indoor house spraying. Knockdown and mortality were recorded at each checkpoint and compared by treatments.

Principal findings

Overall, Fludora Co-Max EW induced significantly higher knockdown and mortality effects in the wild insecticide-resistant Ae. aegypti and Cx. quinquefasciatus compared with K-Othrine EC. With both species, Fludora Co-Max EW mortality rates were above 80% (up to 100%) for outdoor ULV spray at each distance checkpoint (i.e. 10 to 100 m), and 100% for indoor ULV and TF sprays at all level checkpoints (i.e. ceiling, mid-height and floor). K-Othrine EC induced high mortality indoors (97.9-100%), whereas outdoor mortality rapidly declined in Ae. aegypti from 96.7% to 36.7% with ULV, and 85.0% to 38.3% with TF, from 10 to 100 m. For outdoor Fludora Co-Max EW spray, ULV showed both higher knockdown and killing performance Ae. aegypti and Cx. quinquefasciatus compared with TF. Fludora Co-Max EW performed better against Cx. quinquefasciatus compared with Ae. aegypti.

Conclusion/significance

Fludora Co-Max EW induced high mortality and knockdown effects against wild insecticide-resistant Ae. aegypti and Cx. quinquefasciatus Abidjan strains and performed better than K-Othrine EC. The presence of flupyradifurone and transfluthrin (with new and independent modes of action) and FFAST technology in the current Fludora Co-Max EW formulation appears to have broadened its killing capacity. Fludora Co-Max EW is thus an effective adulticide and may be a useful tool for Aedes and Culex mosquito and arbovirus control in endemic areas.

Author Summary

Space spraying of insecticides is an important tool to control Aedes and Culex mosquitoes and prevent the viral diseases (i.e. dengue, yellow fever, etc.) that they transmit. We studied the efficacy of the product Fludora Co-Max EW (a new space spray insecticide) against adult wild insecticide-resistant populations of Aedes aegypti and Culex quinquefasciatus mosquitoes from Abidjan, Côte d’Ivoire. We compared Fludora Co-Max EW knockdown and mortality effects in these mosquitoes with the local insecticide K-Othrine EC using ultra-low volume (ULV) and thermal fogging (TF) spraying outdoors and indoors. The product Fludora Co-Max EW induced high rates of knockdown and mortality (i.e. 80-100%) in these wild insecticide-resistant mosquitoes and performed better than the product K-Othrine EC. Additionally, ULV sprays of Fludora Co-Max EW demonstrated higher knockdown and killing efficacy at larger distances (i.e. up to 100 m) compared with TF. The higher efficacy of Fludora Co-Max EW may be due to the interaction of two unrelated insecticides, flupyradifurone and transfluthrin, in combination with Film Forming Aqueous Spray Technology (FFAST). Fludora Co-Max EW therefore appears to be an effective and useful tool to control adult populations of wild insecticide-resistant Aedes and Culex mosquitoes and may be recommended for preventing related mosquito-transmitted viral diseases.