Author(s)

Kopya Edmond^1,2*, Foko Dadji Gisele Aurelie³, Sonhafouo-Chiana Nadège^2,4, Bamou Roland^2,5, Djamouko-Djonkam Landre^2,5, Talipouo Abdou^1,2, Delogko Serges³, Njiokou Flobert¹, Awono-Ambene Parfait², Wondji Charles Sinclair^6,7, Antonio-Nkondjio Christophe^2,7*

¹Faculty of Sciences, University of Yaoundé I, Yaoundé, Cameroon.
²Laboratoire de Recherche sur le Paludisme, Organisation de Coordination pour la lutte Contre les Endémies en Afrique Centrale (OCEAC), Yaoundé, Cameroun.
³High Teacher School, University of Yaoundé I, Yaoundé, Cameroon.
⁴Faculty of Sciences, University of Buea, Buea, Cameroon.
⁵Vector Borne Diseases Laboratory of the Biology and Applied Ecology Research Unit (VBID-URBEA), Department of Animal Biology, Faculty of Science of the University of Dschang, Dschang, Cameroon.
⁶Centre for Research in Infectious Diseases, Yaoundé, Cameroon.
⁷Vector Group Liverpool School of Tropical medicine Pembroke Place, Liverpool, UK.

Background: With the rapid expansion of insecticide resistance limiting the effectiveness of insecticide-based vector control interventions, integrated control strategies associating larviciding could be appropriate to improve current control efforts. The present experimental study assesses laboratory and field efficacy of the larvicide VectoMax^®G on Anopheline and Culicine larval stages in Yaoundé. Methods: The effect of the larvicide VectoMax^®G, a combination of Bacillus thuringiensis var. israelensis (Bti) and Bacillus sphaericus (Bs), on larval development was assessed during both laboratory and open field trial experiments. Laboratory experiments permitted the evaluation of five different concentrations with four replicates/experiments. Laboratory experiments were conducted with Anopheles coluzzii “Ngousso” and Culex quinquefasciatus laboratory strains. Open field trials were conducted using sixteen plastic containers with a diameter of 0.31 m buried in an array of four rows with 4 containers each. Distance between rows and between containers in a row was 1 meter. This experiment permitted to test the effect of the microbial larvicide VectoMax^®G under operational application conditions on field mosquito populations. Results: The time to induce 100% mortality after exposure to serial concentrations of the larvicide varied according to the dose from 4 - 12 hours for An. coluzzii and 6 - 9 hours for Cx. quinquefasciatus in laboratory experiments. Measurements of the residual activity indicated that all VectoMax^®G concentrations were still active after 35 days and killed 86% - 100% of larvae. Lethal dose of VectoMax^®G killing 50% of larvae was estimated at 5.24 × 10^-8 mg/m² for An. coluzzii and 1.25 × 10^-8 mg/m² for Cx. quinquefasciatus. The lethal concentration inducing 95% mortality was estimated at 3.13 × 10^-7 mg/m² for An. coluzzii and 2.5 × 10^-8 mg/m² for Cx. quinquefasciatus. Open field trials tests indicated that sub-lethal concentrations of VectoMax^®G successfully killed 100% An. gambiae s.l. larvae within 24 hours, while with Culex spp. larvae, 100% mortality was recorded after 48 hours post-treatment. Natural recolonization of water containers by larvae was recorded between 3 and 6 days respectively after the treatment with sublethal doses. Late instar larvae were recorded 5 and 6 days after treatment. When the jars were treated with reference dosage or supra doses of VectoMax^®G, recolonization of water containers was observed six days after treatments. No pupae of both species were found 6 and 7 days post-treatment. Conclusions: The study indicated high efficacy of the microbial larvicide VectoMax^®G against Anopheline and Culex larvae. Microbial larvicides such as VectoMax^®G could be appropriate for controlling mosquito population particularly in areas experiencing high insecticide resistance or outdoor biting mosquitoes.

VectoMax^®G, Bacillus thuringiensis var. israelensis, Bacillus sphaericus, Anopheles gambiae s.l., Culex Mosquitoes, Yaoundé, Camreroon

Edmond, K. , Dadji Gisele Aurelie, F. , Nadège, S. , Roland, B. , Landre, D. , Abdou, T. , Serges, D. , Flobert, N. , Parfait, A. , Charles Sinclair, W. and Christophe, A. (2022) Efficacy of the Microbial Larvicide VectoMax^®G against Anopheles gambiae s.l. and Culex spp. Larvae under Laboratory and Open Field Trial Experiments in the City of Yaoundé, Cameroon. Advances in Entomology, 10, 34-51. doi: 10.4236/ae.2022.101003.