Microbial larvicides for malaria control in The Gambia

Area of Science:

• Vector Control
• Medical Entomology
• Environmental Science

Background:

• Mosquito larval control is crucial for integrated vector management (IVM) to reduce malaria transmission.
• Assessing microbial larvicides against Anopheles gambiae s.l. is vital for large-scale programs in The Gambia.

Purpose of the Study:

• Evaluate the efficacy of Bacillus sphaericus (Bs) and Bacillus thuringiensis var. israelensis (Bti) against Anopheles gambiae.
• Determine residual effects, optimal re-treatment intervals, and operational application methods.
• Assess susceptibility of local vectors to commercial microbial larvicide formulations.

Main Methods:

• Laboratory and field trials of water-dispersible (WDG) and corn granule (CG) formulations of Bs and Bti.
• Testing susceptibility, residual activity, and operational effectiveness under varied conditions.
• Developing methods for large-scale application and personnel training.

Main Results:

• High susceptibility of Anopheles gambiae s.s. to both Bs and Bti microbials.
• Bs showed limited residual effect, while Bti had some residual effect up to 10 days in dry conditions.
• Weekly application of both microbials achieved 100% larval mortality and significant pupal reduction, with successful operational control for three months.

Conclusions:

• Environmentally safe microbial larvicides significantly reduce mosquito larval abundance in The Gambia.
• These larvicides are valuable tools for integrated vector management (IVM) strategies against malaria.
• Formulations with enhanced residual effects could reduce intervention costs.