Using ovarian development stages in the determination of the physiological age in the females of Anopheles gambiae s.l, south-eastern Benin

Background: The physiological age of vectors is an indicator often used in the evaluation of the efficacy of malaria vector means. The purpose is to study the ovarian development stage for the determination of the physiological age of mosquitoes. Methods: Mosquitoes were collected using human landing catch at night in the district of Itassoumba and Abomey-takplikpo, south-eastern Benin. Females An. gambiae s.l were identified morphologically using the determination keys. The ovaries were dissected in distilled water. Additionally, one ovary is cut and transferred into Natrichlorid physiological liquid for the reading of ovarian development stage. Mosquitoes, which are between the stages I and II-young are nulliparous and those which are between IImean and III are parous. After drying, the tracheoles of ovary left in distilled water were examined with the usual Detinova method. Results: Among 271 An. gambiae s.l examined at Itassoumba, 72 were nulliparous with the reading of ovarian tracheoles against 66 with the reading of the ovarian development stages (P=0.61). With the 199 remaining identified mosquitoes as parous with the examination of tracheoles, the reading of the ovarian development stages has recognized 173 as parous (P=0.18). At Abomey-takplikpo, on 197 specimens examined, 52 and 49 were nulliparous respectively with the reading of tracheoles and the examination of the ovarian development stages (P=0.71). Among the 145 remaining mosquitoes identified as parous with the tracheoles method, 119 were parous with the examination of the ovarian development stages (P=0.12). Conclusion: The development stages of ovaries are usable for the determination of the physiological age of mosquitoes. Nulliparous mosquitoes are between the stages I and II-young. However, parous are between the stages II-mean and III.