Introduction

Mosquitoes are small slender bodied insects that feed on man and other animals for blood meals. They are widely distributed in both tropical and temperate regions of the world. Mosquitoes are strongly attracted to humans and are especially adapted to breeding in places created by human activities. Agricultural or farming practices such as irrigation system, fish ponds and use of water storage containers in livestock houses provide suitable breeding ground for anthropophilic mosquitoes. Also, poor housing conditions may increase man vector contact. Bushes, garbage heaps, swamp and stagnant pools of water or surface water provide hospitable breeding ground for the mosquitoes. The increase in environmental modification as a result of urbanization is usually being accompanied by creation of more breeding sites for mosquitoes which most often lead to the increase in the incidence of mosquito borne diseases (Amusan et al., 2003).

There are variations in the ecology of mosquitoes within and between countries of the world which is an integral part of the epidemiology of mosquito borne diseases. It is generally agreed that a clear understanding of the detailed ecology of mosquitoes is a pre-requisite for effective control of mosquito borne diseases. Tropical areas including Nigeria have the best combination of adequate rainfall, temperature and humidity, allowing for breeding and survival of different species of mosquitoes. Larval survey of mosquitoes can be used as an indicator of the risk of mosquito borne diseases transmission in a given area. This is because species specific preference for certain breeding sites has resulted in development of species sanitation programmes which usually achieved great success in different mosquito borne disease control in endemic parts of the world in early 20th century (Takken et al., 1991; Bradley, 1994). The application of larval control approach is considered an effective method of mosquito control and for the campaign to be successful, the type of habitat must be considered.  Subsequently, the most productive habitat should be given a priority attention.

Breeding sites of mosquitoes seem to persist in riverine communities. This is because of the presence of water required for egg laying in the lifecycle of mosquitoes and this could be provided all seasons in riverine communities. It then means that different mosquito species are likely to be found there; which may pose serious risk of mosquito borne diseases. However, there is no information on the mosquito fauna and mosquito borne diseases present in some riverine areas of South Eastern Nigerian. Aguleri was chosen because it is a riverine community and the only reported mosquito borne disease there is malaria (Egbuche et al., 2013). This research was therefore conducted to identify the mosquito species breeding in Aguleri. This would be used as an indicator of the risk of mosquito borne diseases transmission in the area.

1 Methodology

The study was carried out at Aguleri in Anambra East Local Government Area of Anambra State. Aguleri is a medium sized town in the South Eastern part of Nigeria. Aguleri is located in latitude 6^o21'N and longitude 6^o53'E. The climatic condition of the area is characterized by two distinct seasons, the wet and the dry seasons, the former takes place between April and October, while the latter occurs from November to March. Aguleri is a rural community with a fertile soil. The majority of the inhabitants are farmers and petty traders, with few civil servants, students and other professionals. Different kinds of food crops both for home consumption and commercial purpose are being grown there. According to National population commission (2006), Aguleri has a population of about thirty nine thousand and seventy five persons (39, 075). Recently there is a huge influx of people from different parts of Nigeria and beyond into Aguleri which has necessitated massive construction activities and opening up of areas that are unoccupied.

1.1 Ethical consideration

A letter of introduction was collected from the Head, Parasitology and Entomology Department, Nnamdi Azikiwe University Awka. This was presented to the Ward Development Chairmen (WDC) who made it possible for me to obtain cooperation from members of their various communities in Aguleri. Verbal consent was obtained from the people whose compounds were used for the study.

1.2 Selection of breeding sites

Three communities (Ivite, Eziagulu and Enugu) were randomly selected for the study. In each of the communities, every container with water or water body identified was considered a potential breeding site. The positive sites were those that had at least one larva in the habitat. The numerous breeding sites encountered were grouped into two major habitats: open and closed habitats.

1.3 Collection of mosquito larvae

Mosquito larvae were collected in the day time between 8.00 am and 12.00 noon. Sampling of mosquito larvae was done using either larval net or dipper method (WHO, 2003) depending on the nature of the habitat encountered. In using the dipper method, a white enamel dipper was lowered gently into the water at an angle of about 450 until one side was just below the surface of the water. Skimming through the surface of the water, the dipper was used to collect mosquito larvae. Dipping was done severally especially in the closed habitats to see if larvae were present. Each content of the dipper after dipping was properly observed for the presence of mosquito larvae. Collected larvae were transferred to a bottle using a plastic bulb pipette. In the water bodies encountered, a larval net was used to collect mosquito larvae. In collecting the larvae, the water surface was swept by holding the net at an angle and moving it through the water. Mosquito larvae that swept into the net were first washed into a basin and then collected in a plastic bottle. Samples collected were labeled accordingly and transported to National Arbovirus and Vector Research Centre (NAVRC) Enugu for rearing and identification.

1.4 Rearing and identification of mosquitoes collected

Mosquito larvae from different habitats were separately reared to adult for proper identification. The larvae were reared in the insectary of National Arbovirus and Vector Research Centre (NAVRC) Enugu under room temperature. Each collection from a given breeding site was emptied into a well labelled white plastic bowl and kept on the laboratory bench. The larvae were fed by the introduction of cabin biscuit sprinkled in the basin. Care was taken not to add too much feed in the basin to avoid suffocation of the larvae. Developed pupae were sorted from the larvae, transferred to a different container and put in a separate cage for adult emergence. Feeing was continued until all the larvae pupated. Emerged adults were collected using an aspirator and transferred into a test tube. Identification of the adult mosquitoes was done with the aid of a dissecting microscope using the identification key by Gillett (1972) and Gillies and Coetzee (1987).

1.5 Statistical analysis

Data were analyzed using SPSS version 20.0. The statistical tools used were chi square and simpsons index of diversity (ED).

2 Result

A total of 429 mosquitoes larvae collected emerged as adults and were identified; 355 from the open larvae habitat and 74 from the closed larvae habitat. They included: Aedes aegypti (39.9%), Ae. albopictus (19.6%), Ae. circumlutoelus (1.2%), Anopheles gambiae (18.9%), An. funestus (1.4%), An. moucheti (1.6%), Culex quinquefasciatus (13.1%) and Cx. tigripes (4.4%). In open larval habitat, three genera (Anopheles, Culex and Aedes) of mosquitoes were identified whereas in the closed habitat, only two genera (Culex and Aedes) were identified.  All the eight different species of mosquito collected were found in the open larval habitat. Only two species (Aedes aegypti and Culex quinquefasciatus) were identified in the closed habitat. The distribution and abundance of the different mosquito species collected in their various breeding sites is shown in Table 1 and Table 2.

Table 1 Abundance and distribution of mosquitoes in closed larvae habitat.

Table 2 Abundance and distribution of mosquitoes in open larvae habitat.

13.5% (48/355) of the mosquitoes from the open larval habitat were collected from ground pool, 28.2% (100/355) from gutter, 23.9% (85/355) from domestic containers, 27.9% (99/355) from other containers in the environment and 6.5% (23/355) from the river banks. The most abundant mosquito species collected in ground pool, gutter, domestic container, other containers and bank of streams/ rivers were An. gambiae, An. gambiae, Cx. quinquefasciatus, Ae. aegypti  and An. Gambiae, respectively. On the overall, the most abundant genera of mosquito collected in the open larvae habitat was Aedes while the most abundant species collected in the open larvae habitat was Ae. aegypti.

In the closed larval habitat, 85.1% (63/74) of the mosquitoes were collected from toilet/ bathroom floor and 14.9% (11/74) were collected from broken septic tank. The most abundant mosquito species collected from both Toilet / bathroom floor and broken septic tank was Ae. aegypti. On the overall as well, the most abundant genera of mosquito collected in the closed larvae habitat was Aedes and the most abundant species collected in the closed larvae habitat was Ae. aegypti.

3 Discussion

The study sought to identify the mosquito species breeding in Aguleri town of Anambra state. The three genera of mosquito encountered were evenly distributed in the study area (ED=0.75). This shows that they are the major genera of mosquito found in the study area. Aedes and Culex mosquitoes were found in both open and closed larvae habitats; though more in open larvae habitat. Anopheles mosquitoes were encountered in open larvae habitat only. The distribution of these genera of mosquito in open and closed larvae habitat was statistically significant (P=0.00, X²=28.8, df=2). It then means that the type of larvae habitat obtainable in any place would determine the mosquito genera that would be encountered in such place. This shows that the mosquito genera have their preferred choice of larvae habitat. Even in the open larvae habitat, there is also significant difference (P=0.00, X²=130.7, df=6) in the distribution of mosquito genera in the various breeding sites encountered. Aedes mosquitoes were found mostly in containers, Culex mosquitoes were also found mostly in containers whereas Anopheles mosquitoes were found in least number in containers. However the distribution of the mosquito species in the study area was not uniform (ED=0.49); Ae. aegypti and Ae. albopictus tend to be more abundant and use almost all the breeding sites encountered than other species.

All the mosquito species identified are man biting mosquitoes; thus they are of public health importance. The females of these species of mosquitoes are blood sucking pests and while feeding on blood of their hosts transmit extremely harmful diseases such as malaria, yellow fever and filariasis as well as other mosquito borne diseases. The presence of one genera or species of mosquito in different types of breeding sites or habitat shows that a female mosquito does not lay her entire batch of eggs in one location, rather she distributes them in many water filled containers or wherever there is pool of water.

In conclusion, the outcome of this research is a useful indicator of the risk of mosquito borne diseases transmission in the study area. The information provided by this research would be helpful in planning and implementation of larval control approach as a method of mosquito control.

References

Amusan A.A.S., Mafiana C.F., Idowu A.B., and Oke O.A., 2007, A survey of adult mosquitoes in the hostels of the University of Agriculture, Abeokuta, Ogun state Nigeria, Nigerian Journal of Parasitology, 24: 167-172

http://dx.doi.org/10.4314/njpar.v24i1.37822

Bradley D.J., 1994, Watson, Swellengrebel and species sanitation: environmental and ecological aspects, Parasitologia, 36: 137-147

Egbuche C.M., Eneanya C.I., Aribodor D.N., Eneanya, O.A., Ogbuagu C.N., and Ezugbo-Nwobi I.K., 2013, Malaria prevalence and use of insecticide-treated net among community members in Aguleri, Anambra State, Nigeria, The Bioscientist, 1(1): 60-66

Gillett J.D., 1972, Common African mosquitoes and their medical importance, William Heinemann Medical books LTD: London, pp. 106

Gillies M.T., and Coetzee M., 1987, A supplement to the anophelinae of Africa South of the Sahara (Afrotropical region), A publication of the South African Institute for medical research, Johannesburg, 55: 143

Takken W., Snellen W.B., Verhaue J.P., Knols B.G.J., Atmosoedjono S., Swellengrebel N.H., and Kuipers J., 1991, Environmental measures for malaria control in indonesia: a historical review on species sanitation, The Netherlands: Wageningen Agricultural University, pp. 32

World Health Organisation, 2003, Sampling malaria vectors, Malaria entomology and vector control, 3: 21-34