DIVERSITY AND VECTORIAL SYSTEM OF ANOPHELINE MOSQUITOES (DIPTERA: CULICIDAE) IN SELECTED ECO-SETTINGS OF NASARAWA STATE, NIGERIA

Abstract

Mosquitoes are known to constitute nuisance as well as transmit disease-causing organisms (pathogens) to hosts. This study was aimed to determine species distribution, abundance, and diversity of mosquitoes in three selected eco – settings of Nasarawa State, Nigeria. Anopheles mosquitoes were sampled using Pyrethroid Spray Catch (PSC and Centre for Disease control light traps CDC) technique the mosquitoes were identified morphologically using keys. Knockdown resistance (Kdr) was determined following standard protocols. Meal preference was determined using Enzyme Linked Immuno Sorbent Assay (ELISA). Collected mosquitoes were classified based on physiological conditions. Molecular forms of the Anopheline species were determined following standard methods. Six (6) species of Anopheles mosquito vectors were encountered in all the selected eco – settings of Nasarawa State: Anopheles gambiae s.l, An. funestus, An. nili, An. coustani, An. rufipes and An. pharoensis. A total of Fifteen thousand, four hundred and seventeen (15,417) mosquitoes vector were encountered in the study areas between the months of January to December, 2017. Most of the mosquitoes encountered were Anopheline (64.09 %). Analysis revealed significant variations in the relative abundance of mosquito and distribution of the vector across the eco – settings studied. The highest number of mosquitoes was caught in the month of May 2017 (1,273; 12.88 %). An. gambiae s.l were the most dominant species (41.89%) encountered across the eco – settings during the two seasons followed by An. coustani (19.49 %). Indoors An. gambiae s.l. collection accounted for 68.21 %. The indoor resting density was 4.46, 3.99 and 3.65 man/hour/night, for sparse woodland, wooded grassland, and swampy grassland, respectively. Wet season accounted for 57.24 % of the vectors collected. Abdominal conditions analyses revealed 27.40 % were half gravid, 26.08 % were gravid and 25.97 % were freshly fed. The highest HBR was recorded in the month of May 2017 (18.30, 22.90, and 23.00 bites/man/hour, for sparse woodland, wooded grassland, and swampy grassland, respectively). Molecular analyses revealed S form An. gambiae s.s constituted 64.47 % of the collection, while 15.47 and 10.93 % were M form An. colluzzi and An. arabiensis. The sporozoite rate was 20.20 % in swampy grassland, 13.20 % in sparse woodland, and 12.80 % in wooded grassland. For the Kdr analyses, 19.02 % of the vectors were (RR) resistant, 31.66% were (RS) heterozygous susceptible and 50.51% were (SS) Susceptible in the study area. Blood meal source analyses revealed 47.47 % was from human, 30.54 % from bovine, and 21.72 % from goats for the study area. Anopheles gambiae s.s had 95.95 % blood meal from human, 45.07 % from bovine and 33.66 % from goats also for single blood meal source 98.56 % was from humans, 44.44% from bovine and 28.32% from goats. Anopheles arabiensis obtained 1.44 % of blood meal source from human, 55.56 % from bovine and 71.67 % from goats mixed blood meal source. Anopheles arabiensis obtained 24.30, 30.43, 33.85, 54.55 % from human/goat, human/bovine, human/bovine/goat and bovine/goats, respectively. This study revealed that Anopheles species were higher in terms of abundance which is very important vectors of malaria in Nigeria. These results indicated that vectors of mosquito-borne diseases are breeding in the study area, most of which are encouraged by human activities.