Larvicidal Potency of Essential Oils of Ocimum suave against Anopheles gambiae Mosquitoes in Delta State

This study was carried out to determine the larvicidal potency of Ocimum suave against Anopheles gambiae mosquitoes in Delta State, Nigeria. Mosquitoes were collected in the early hours of the morning from breeding sites across Aniocha North and South LGAs. Puddles, gutters, and stagnant water were inspected for immature stages, which were collected using dippers. The immature stages were allowed to acclimatize in the insectary under controlled conditions until they developed into fourth-instar larvae. The experiment adopted a completely randomized design (CRD) with three replicates. Larval mortality was recorded, and lethal times for 50% and 95% of the larvae were determined. Key findings revealed that larval mortality increased significantly with both concentration and exposure time. All concentrations (5–100 ppm) produced complete larval mortality within 24 hours. The 100% PPM concentration caused the highest mortality between 40 and 60 minutes (p < 0.0001). Lethal time (LT₅₀) values ranged between 52.6 and 65.2 minutes, while LT₉₅ values ranged between 100.0 and 123.9 minutes. GC–MS analysis showed that linoleic acid (24.9%) was the most abundant compound, while stigmasterol exhibited the highest retention time (37.5 minutes). Conclusively, the essential oil of O. suave demonstrates strong larvicidal activity and has potential for use as a plant based larvicide against Anopheles gambiae. These findings highlight its promise for incorporation into larval source management programs aimed at reducing vector emergence and abundance. Future studies are required to evaluate its field performance under natural environmental conditions.