Potential Repellent and Insecticidal Effects of Millipede-derived Secretions Against Anopheles gambiae s.l., the Main Malaria Vector in Africa

Chemical insecticides have greatly contributed to the emergence of resistant mosquito populations in sub-Saharan Africa. Innovative strategies exploring novel animal-derived secretions may offer new avenues for effective vector control. We investigated the chemical composition of the hydroethanolic extract (HE) from millipede Ophistreptoides sp. and assessed its repellent and insecticidal effects against the susceptible Anopheles gambiae Kisumu strain. Millipedes were collected from vegetation and macerated in 70% distilled alcohol and 30% tap water for 5 days. A spectrophotometric approach was performed for the determination of all compounds present in the extract. The repellent effect was evaluated on fifty adult females of An. gambiae using impregnated papers with extract at different concentrations of 25, 50, 75, and 100 mg/mL, with acetone as control. The adulticidal effect was measured after 1 hour of exposure, with mortality assessed at 24, 48, and 72 hours post-exposure. Spectrophotometric analysis identified 2-2-methoxy-3-methyl-1,4-benzoquinone and methyl-1,4-benzoquinone as the main compounds in the extract. The repellency rate ranged from 57.69 ± 11. 46 at 25 mg/mL concentration to 97.54±1.42% at 100 mg/mL concentration. Mosquito mortality rates increased significantly ( p < 0.05) with both exposure time and tested concentration with the highest toxicity recorded at 72 h post-exposure (LC 50 = 18.09 mg/mL; LC 95 = 186.44 mg/mL). This study highlights the potential of millipede-derived bioactive compounds in integrated vector management and suggests further research into their molecular modes of action and formulation for mosquito nets and spray.