Seasonal variation and relative abundance of drainage breeding mosquito species in Imo State, Nigeria

An ecological study of drainage - breeding mosquito vectors was conducted in the three urban centers (Owerri, Orlu and Okigwe) of Imo State, Nigeria. Twelve drainage sites located around markets, residence, streams and hotels were selected in each urban centre. Dipping method of sampling was employed and a total of 8,820 mosquitoes comprising eight species namely; Aedes aegypti, Aedes vittatus, Culex quinquefasciatus, Culex tigripes, Culex horridus, Culex cinereus, Culex annuliorus and Anopheles gambiae were encountered; in Owerri and Orlu with Cx. cinereus being completely absent in Okigwe. Cx. quinquefasciatus was predominantly present in all drainage sites with the highest occurrence of (372.83) followed by Aedes aegypti (151.17), An .gambiae (78.75), Cx. tigripes (40.25) Ae. vittatus (35.00), Cx. horridus( 22.00), Cx.cinereus( 21.75), Cx. annuliorus (13.25). Of all sites sampled, market drainages had the highest abundance of mosquitoes which was significantly higher than (ANOVA, P? 0.05) the residential, stream and hotel drainages. Residential drainages recorded second highest density followed by stream and hotel drainages had the least. The abundance of mosquitoes in Owerri (130.06) the State Capital was significantly higher (ANOVA, P? 0.05) than in Orlu (93.44) and Okigwe (52.13). Result of the Pearson correlation (2 - tailed) analysis showed significant correlation between mosquito abundance and rainfall in the three urban centers of Imo State with highest abundance in June. This work has actually provided information on 8 species associated with drains in the State together with the seasonality of these arsenals. During dry months, Culex species were found to be dominant while in rains Aedes and Anopheles. Possibly, effective larviciding against these various species could be targeted in these months.