Palp ratio as a field identification tool for two members of the Anopheles gambiae complex in Ghana (A. melas and A. gambiae)

BACKGROUND: The Anopheles gambiae Giles complex is the most widely studied and the most important insect vector group. We explored the use of the palp ratio method as a field tool to identify A. melas and A. gambiae in Ghana. METHODS: Human landing catches were conducted to collect mosquitoes in the coastal area of Western Region of Ghana. Palps were removed and segments 3 and 4 + 5 measured using a compound microscope. DNA extraction and downstream PCR for species identification was carried out using the legs and wings. Known A. gambiae collected from the Ashanti Region of Ghana were used for comparison. RESULTS: A total of 2120 A. gambiae were collected. Lengths of segments 3 and 4 + 5 were significantly correlated in samples from both regions. Using a palp ratio of 0.81 as the cut-off value, 14.9 % outliers (≥0.81) from our study area were confirmed by PCR as A. melas. PCR also confirmed outliers from the Ashanti Region with palp ratio < 0.81 (10.2 %) as A. gambiae. CONCLUSION: The palp ratio method proved to be a useful tool to identify populations of salt and freshwater A. melas and A. gambiae.