Adulticidal and post-exposure reproductive effects of crude n-hexane leaf extract of Ocimum suave Willd. on Anopheles gambiae s.l.

• Esther U. Kadiene

  DELTA STATE UNIVERSITY, ABRAKA

  Author

• Victor Enwemiwe

  Author

• Eric Esiwo

  Author

• Isaac Ighoyivwi

  Author

• Ehimwenma Aghahowa

  Author

• Precious Edhebe

  Author

• Sarah Ifeta

  Author

• Chioma Ojianwuna

  Author

Background: Insecticide resistance increases the need for complementary mosquito-control agents. This study evaluated the adulticidal and post-exposure reproductive effects of a crude n-hexane leaf extract of Ocimum suave Willd against field-derived Anopheles gambiae s.l.

Methods: The extract was formulated in olive oil at nominal concentrations of 0.05%, 0.25%, 0.75%, 1.00%, 4.00% and 7.50% (v/v) and evaluated using the WHO tube-bioassay framework. Twenty-five non-blood-fed females aged 3-5 days were tested per tube, with four exposure replicates and two olive-oil controls per concentration. A parallel assay evaluated mosquitoes pre-exposed to 4% piperonyl butoxide (PBO).

Results: Extract-only 24-h mortality increased from 24% at 0.05% to 70% at 7.50%, while PBO pre-exposure increased mortality to 56-91% across the corresponding concentrations. All 60-min knockdown values remained below 25%; therefore, KDT50 and KDT95 were not estimable within the observation period. Exposed females produced fewer eggs than control females (1.33 ± 0.44 versus 4.39 ± 0.74 eggs), and a negative-binomial model estimated an incidence-rate ratio of 0.304 (95% CI: 0.147-0.627; p = 0.0013). No hatching was recorded among eggs produced by exposed females.

Conclusion: The concentration-related adult mortality, PBO-associated enhancement and model-supported post-exposure reproductive response support further chemical standardization and vector-control evaluation of O. suave crude leaf extract.

1. Esther U. Kadiene, DELTA STATE UNIVERSITY, ABRAKA

   Department of Animal and Environmental Biology

2. Victor Enwemiwe

   Department of Animal and Environmental Biology

3. Eric Esiwo

   Department of Animal and Environmental Biology

4. Isaac Ighoyivwi

   Department of Animal and Environmental Biology

5. Ehimwenma Aghahowa

   Department of Animal and Environmental Biology

6. Precious Edhebe

   Department of Animal and Environmental Biology

7. Sarah Ifeta

   Department of Animal and Environmental Biology

8. Chioma Ojianwuna

   Department of Animal and Environmental Biology

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