BIONOMICS AND DISTRIBUTION OF MAN-BITING MOSQUITOES IN ORAIFITE, EKWUSIGO LOCAL GOVERNMENT AREA, ANAMBRA STATE, NIGERIA.

SOURCE:

Faculty: Biosences
Department: Parasitology And Entomology

CONTRIBUTORS:

Obi, O.J;
Onyali, I.O;

ABSTRACT:

Rapid increase in infrastructural development and human population influx into Oraifite in Anambra State, Nigeria has resulted in environmental modifications with multiple mosquito breeding habitats in the area, hence the need for the study. The aim was to study the bionomics and distribution of man-biting mosquitoes in Oraifite, Ekwusigo L.G.A., Anambra State. The objectives were to determine mosquito species composition at morphological and molecular level; the breeding sites of the mosquito vectors; the ecological factors that influence the survival of mosquitoes in their breeding sites and temporal distribution of the mosquito vectors in relation to the climatic factors. This study was done between January 2017 and July 2018. Eight communities (two from each of the 4 quarters of Oraifite) were randomly selected. The communities were Amakom, Ibolo, Nkalafia, Umuafa, Umudisi, Umuezopi, Umunakwa and Umuonyeagolu. The study was a field longitudinal survey of mosquitoes and their breeding sites in the community. Three houses were sampled twice monthly in each community. Indoor and outdoor adult mosquitoes were sampled by pyrethroid knockdown collection and human bait catch methods. The collected mosquitoes were identified morphologically using identification keys and molecularly by polymerase chain reaction (PCR) technique. Mosquito breeding habitats were sampled for larvae using dipping method. Physicochemical parameters (pH, salinity, total suspended solids, total dissolved solids, dissolved oxygen, sulphate and surface water temperature) of water in larval habitats were determined by conventional methods while temperature, rainfall and relative humidity of the area were obtained from Weather Atlas. The data collected were analysed using analysis of variance (ANOVA), correlation coefficient and ecological indices. A total of 1418 indoor mosquitoes belonging to 12 different species were collected. Anopheles gambiae 294 (20.73%) topped the list while Coquillettidia maculipennis 1(0.07%) was least. Numbers of indoor mosquito species sampled from the 8 communities were significantly different (p<0.05; P=3.38E-19). Fourteen mosquito species made up the total of 952 mosquitoes collected outdoors. Aedes albopictus 238(25.00%) was the most collected outdoors while Culex nigripalpus 2(0.21%) was the least. Numbers of outdoor mosquito species sampled from the 8 communities were also significantly different (p<0.05; P=1.3E-28). Of the 160 An. gambiae complex subjected to PCR, 125(78.1%) turned out to be An. gambiae sensu stricto. There was significant difference (P<0.05, 1.24E-06) between indoor and outdoor mosquito population collected in the communities. A total of 1156 larval mosquitoes were collected. Man-made containers contributed the highest number 522(45.16%) while the least was from plant axils 134(11.60%). However, there was significant difference (p<0.05; P=1.89E-07) between mosquito species sampled from the studied communities of Oraifite with Aedes albopictus being the most dominant species (Simpson’s dominant index, C = 0.041) and also having the highest Shannon-Wiener index of diversity (H = 0.140). The physicochemical parameters studied indicated that dissolved oxygen was highly significant (p<0.01) with all mosquito larvae abundance. Similarly total dissolved solids had no significant (p>0.05) relationship with larvae abundance in the study area. There was a strong negative correlation between indoor and outdoor mosquito abundance and environmental temperature (r = -0.8764 and -0.8978 respectively). However, correlation between indoor and outdoor mosquito abundance and relative humidity (r = 0.8834 and 0.885085), and rainfall (r = 0.9116 and 0.936896) were highly positive. This study has revealed that temperatures between 26.6 ºC and 28.6ºC, relative humidity of more than 85%, and rainfall of more than 138mm were most favourable for the development and maintenance of mosquito species in the study area. The mosquito species of public health importance identified in Oraifite included Ae. albopictus, Ae. aegypti, An. gambiae s.s., An. funestus, Ae aegypti, Cx. quinquefasciatus, Cx. decens. The implication of the presence of these vectors in Oraifite indicates a potential risk of mosquito-borne disease out-breaks in the area. Therefore, strict surveillance and control of mosquitoes should be adopted to prevent the outbreak of mosquito-borne diseases in the study area.