Annual Research & Review in Biology

Aims: This study evaluated the insecticidal and repellent activities of fumigation sticks formulated from Cymbopogon citratus and Ocimum canum leaves against the field mosquito population and mosquitoes surviving exposure to Fatala® mosquito coils collected in Garoua, Northern Cameroon.

Study design:  A laboratory-based experimental and comparative study was conducted to assess the insecticidal and repellent efficacy of fumigation sticks prepared from C. citratus and O. canum against the field mosquito population and the esbiothrin-selected mosquito population.

Place and Duration of Study: The study was carried out in Garoua, Cameroon, using mosquito populations collected from Ngalbidjé, Roumdé-Adja, and Yelwa in August 2025.

Methodology: Mosquito larvae were collected from breeding sites and reared under laboratory conditions until adult emergence. An esbiothrin-selected mosquito population was established by exposing adult mosquitoes to the commercial Fatala® mosquito coil containing esbiothrin and selecting survivors for subsequent bioassays. Fumigation sticks prepared from powdered leaves of C. citratus and O. canum were evaluated at concentrations ranging from 0.6 to 3.0 g/m³. Adult mosquitoes were exposed to fumigation smoke for 1 h, and mortality was recorded at 1, 3, 6, 12, and 24 h post-exposure. Repellent activity was assessed in a 1 m³ chamber using a live vertebrate host as bait, and repellency was estimated by comparing mosquito escape responses between treatment and control chambers. Lethal doses (LD₅₀ and LD₉₅) were estimated by probit analysis.

Results: Both plant species exhibited significant insecticidal activity against the field mosquito population and the esbiothrin-selected mosquito population. Mortality rates increased with both concentration and post-exposure time. O. canum demonstrated slightly greater activity at lower concentrations, whereas C. citratus showed more sustained fumigant efficacy over time. The LD₅₀ and LD₉₅ values progressively decreased with increasing exposure duration, indicating cumulative toxic effects. Although the esbiothrin-selected mosquito population initially displayed lower susceptibility, increasing fumigation concentrations significantly enhanced mortality. Repellency assays revealed strong repellency within one hour for both botanical formulations, with maximum repellency of 90.7 ± 1.3% after 45 min. The efficacy observed was comparable to that of the commercial esbiothrin-based mosquito coil Fatala®.

Conclusion: These findings indicate that C. citratus and O. canum possess substantial insecticidal and repellent activities against field mosquito populations and an esbiothrin-selected mosquito population. The results suggest that these locally available plants may provide promising botanical materials for complementary mosquito control in Northern Cameroon, although confirmation of insecticide resistance using standard WHO methods is still required.