Preliminary Assessment of Bespoke ('X-tec') Silica Particles for IRS Applications

Area of Science:

• Entomology
• Materials Science
• Chemical Engineering

Background:

• Indoor residual spray (IRS) efficacy is influenced by substrate, insecticide concentration, and bioavailability.
• Optimizing insecticide delivery is crucial for effective malaria vector control.

Purpose of the Study:

• To investigate X-tec silica particles as a novel carrier for clothianidin insecticide in IRS formulations.
• To reduce insecticide content while maintaining or improving residual biological activity.

Main Methods:

• Bespoke silica particles (X-tec silica) were engineered with pore sizes to keep clothianidin amorphous.
• Material characterization assessed insecticide loading and physical form within silica pores.
• Bioefficacy tests were conducted against *Anopheles gambiae* s.s. Kisumu on glazed and unglazed tiles at varying application rates and time points.

Main Results:

• 100% mosquito mortality was achieved within 48 hours at 60 and 90 mg a.i./m² on both surfaces at 1 week.
• On glazed tiles, 100% mortality was observed within 48 hours even at the lowest rate (30 mg a.i./m²) after 8 months.
• Lower efficacy was noted on unglazed tiles, particularly at lower concentrations and longer durations, highlighting surface interaction importance.

Conclusions:

• X-tec silica shows potential for enhancing IRS efficacy with significantly reduced clothianidin concentrations.
• The formulation's performance is dependent on surface type, with glazed surfaces showing superior results.
• Further research is warranted to optimize X-tec silica formulations for broad application in IRS programs.