TITLE:
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
AUTHORS:
Kopya Edmond, Foko Dadji Gisele Aurelie, Sonhafouo-Chiana Nadège, Bamou Roland, Djamouko-Djonkam Landre, Talipouo Abdou, Delogko Serges, Njiokou Flobert, Awono-Ambene Parfait, Wondji Charles Sinclair, Antonio-Nkondjio Christophe
KEYWORDS:
VectoMax®G, Bacillus thuringiensis var. israelensis, Bacillus sphaericus, Anopheles gambiae s.l., Culex Mosquitoes, Yaoundé, Camreroon
JOURNAL NAME:
Advances in Entomology,
Vol.10 No.1,
November
30,
2021
ABSTRACT: 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.