A reliable morphological method to assess the age of male <it>Anopheles gambiae</it>

• Main Authors: Killeen Gerry F, Ng'habi Kija R, Huho Bernadette J, Nkwengulila Gamba, Knols Bart GJ, Ferguson Heather M
• Format: Article
• Language: English
• Published: BMC 2006-07-01
• Series: Malaria Journal
• Online Access: http://www.malariajournal.com/content/5/1/62

<p>Abstract</p> <p>Background</p> <p>Release of genetically-modified (GM) or sterile male mosquitoes for malaria control is hampered by inability to assess the age and mating history of free-living male <it>Anopheles</it>.</p> <p>Methods</p> <p>Age and mating-related changes in the reproductive system of male <it>Anopheles gambiae </it>were quantified and used to fit predictive statistical models. These models, based on numbers of spermatocysts, relative size of sperm reservoir and presence/absence of a clear area around the accessory gland, were evaluated using an independent sample of mosquitoes whose status was blinded during the experiment.</p> <p>Results</p> <p>The number of spermatocysts in male testes decreased with age, and the relative size of their sperm reservoir increased. The presence of a clear area around accessory glands was also linked to age and mating status. A quantitative model was able to categorize males from the blind trial into age groups of young (≤ 4 days) and old (> 4 days) with an overall efficiency of 89%. Using the parameters of this model, a simple table was compiled that can be used to predict male age. In contrast, mating history could not be reliably assessed as virgins could not be distinguished from mated males.</p> <p>Conclusion</p> <p>Simple assessment of a few morphological traits which are easily collected in the field allows accurate age-grading of male <it>An. gambiae</it>. This simple, yet robust, model enables evaluation of demographic patterns and mortality in wild and released males in populations targeted by GM or sterile male-based control programmes.</p>