Research

A reliable morphological method to assess the age of male Anopheles gambiae

Bernadette J Huho^1,2 , Kija R Ng'habi^1,2 , Gerry F Killeen^1,3,4 , Gamba Nkwengulila² , Bart GJ Knols^5,6 and Heather M Ferguson^1,6

¹  Ifakara Health Research and Development Centre, PO Box 53, Off Mlabani Passage, Ifakara, Tanzania

²  Department of Zoology and Marine Biology, University of Dar es Salaam, PO Box 35064, Dar es Salaam, Tanzania

³  Department of Public Health and Epidemiology, Swiss Tropical Institute, Socinstrasse 57, Basel, C4-4002, Switzerland

⁴  School of Biological and Biomedical Sciences, Durham University, Durham DH1 3LE, UK

⁵  International Atomic Energy Agency (IAEA), Agency's Laboratories Seibersdorf, Seibersdorf A-2444, Austria

⁶  Laboratory of Entomology, Wageningen University and Research Centre, PO Box 8031, 6700 EH Wageningen, The Netherlands

author email corresponding author email

Malaria Journal 2006, 5:62doi:10.1186/1475-2875-5-62

Published:	27 July 2006

Abstract

Background

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 Anopheles.

Methods

Age and mating-related changes in the reproductive system of male Anopheles gambiae 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.

Results

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.

Conclusion

Simple assessment of a few morphological traits which are easily collected in the field allows accurate age-grading of male An. gambiae. 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.