MATERIALS AND METHODS

Study area: Niger Delta University (6°08'N and 4°57'E) is located in Amassoma community; an ancient community in the wilberforce Island in Southern Ijaw Local Government Area of Bayelsa State. The details of the study locations have been exclusively described by Amawulu et al.¹⁹.

Study design: The study combines both field and laboratory study. A field and cross sectional study design was adopted to identify mosquito breeding sites within the Niger Delta University Campuses during March-May, 2019. It is a cross sectional because the study was carried out at a single visit without necessarily going out for a follow up.

Mosquito sampling and collection: The study was carried out in the Niger Delta University, Amassoma. The study locations were New site and Main campus. In each location, waste dumpsites, water containers, gutters, block holes, motor tyres and water pools were identified and inspected for the presence of mosquito larva. Larva were either collected using giant plastic pipette where they are found in small container or the entire container contents were upturn into collection vessels. In a deeper water body, larva was collected with a ladder following the dip method described by Service²⁰. The procedures for dipping and larva collection has been described in Amawulu and Amakiri²¹. Collected samples were labeled according to the macro habitat.

Morphological identification: Identification of mosquito larvae were done as per standard keys^22-23. The position of the head and abdomen in relation to the water body was used to separate the Anopheles from Culex and Aedes.

Measurement of physico-chemical parameters: The physico chemical parameters such as water temperature, pH, Biochemical oxygen Demand (BOD), turbidity and conductivity were determined at the Quality Control Laboratory, Niger Delta University, Bayelsa State.

Statistical analyses: Two statistical tools used for statistical analysis were simple percentage and ANOVA. Simple percentage was used to show the distribution of mosquito larva in different micro habitats and locations. The relation between larva abundance and microhabitats were all determined using ANOVA at p = 0.05. Karl Pearson’s correlation matrix was used to assess the relationships between larva abundance and the physicochemical parameter.

RESULTS

Three thousand and five hundred mosquito larva was collected from five micro habitats across two locations in Niger Delta University Campuses during March-May, 2019. The population of Culex quinquefasciatus larva (66.86%) were more than Anopheles gambiae sl. larva (33.14%). The differences were significant (t = 2.966, df = 1, p<0.05) (Table 1).

Mosquito Larva productivity across breeding sites in Niger Delta University (March-May, 2019): Five mosquitoes breeding sites were identified. These are; motor tyres, gutter, containers, water pools and block holes. Triplicate of each kind of microhabitats were inspected for mosquito larva. When the mosquito larva was pooled into breeding sites (Fig. 1), more mosquito Larvae was recovered in containers, followed by block holes. The least was recovered in motor tyres.

Culex and Anopheles mosquito species were sympatric in all the breeding sites. The mean and standard deviation of the Culex quinquefasciatus larva productivity across the microhabitat were in the order, CT>BH>MT>GT>WP. The mean and standard deviation of Anopheles productivity across breeding sites in their increasing order of abundance were CT>GT>MT>BH>WP, respectively. Differences in the mosquitoes’ larva productivity across the breeding sites was significant (t = 4.715, p<0.05).

Relationships between physico-chemical parameters and mosquito larva productivity: The effect of physico chemical parameters on larva population varied across the breeding sites. The mean pH was highest in block hole and least in motor tyre; Temperature was slightly uniform in all breeding sites and ranges from 25.80-28.03°C. The mean turbidity was highest in water pool and least in gutter, although the differences was not significant (p>0.05). The mean salinity (ppm) ranges from 0.32-12.93, with a significant higher value in water pool. The mean conductivity and alkalinity were not significantly different across the breeding sites. The mean chlorides differ significantly between block hole, water pool and containers (Table 2).

Culex quinquefasciatus larva productive was significantly higher than A. gambiae larva in all the breeding sites (t = 2.966, p<0.05). The larva productivity was influenced by physico chemical parameters (Ph, T^O, Turbidity, Salinity, Conductivity, Alkalinity and Chlorides). A correlation matrix analysis (Table 3) shows that relationship exist between physico chemical parameters and mosquito larva productivity. Culex quinquefasciatus larva had a positive correlation with temperature, Turbidity, salinity and conductivity, However, a negative correlation exist between Culex mosquito and alkalinity.

Table 1:	Population of mosquito fauna in NDU, March-May, 2019

Fig. 1:	Percentages of mosquito larva species across five micro-habitats
	MT: Motor Tyre, GT: Gutter, CT: Container, WP: Water pool, BH: Block holes

Table 2:	Mosquito Larva productivity across breeding sites in Niger Delta University, during March-May, 2019
***BH: Block hole, WP: Water pool, CN: Container, MT: Motor tyre, GT: Gutter, **TO: Temperature, pH: Hydrogen ion concentration, TUD: Turbidity, Sal: Salinity, COND: Conductivity, ALK: Alkalinity, CL: Chloride, *Different alphabets a, b and c on each column indicates a significant difference between containers at alpha level p<0.05. There was a significant difference between treatment value among containers at p<0.05, Values are presented as Mean±standard deviation

Table 3:	Correlation between mosquito larva productivity and physico-chemical parameters
TO: Temperature, pH: Hydrogen ion concentration, TUD: Turbidity, Sal: Salinity, COND: Conductivity, ALK: Alkalinity, CL: Chloride, *Different alphabets a, b and c on each column indicates a significant difference between containers at alpha level p<0.05. There was a significant difference between treatment value among containers at p<0.05

Nevertheless, Culex larva productivity was significantly influenced by pH. Anopheles gambiae larva productivity showed a positive correlation with temperature, pH and alkalinity but were negatively correlated with Turbidity, salinity, conductivity and Chlorides. However, the increased productivity of Anopheles mosquito in some breeding sites was influenced by pH While their reduced productivity in some breeding sites was influenced by salinity.

DISCUSSION

The knowledge about the ecology and factors that affects the breeding of mosquitoes is a germane to predict the likelihood of mosquito borne diseases. In this present study, Culex quinquefasciatus and Anopheles were the only mosquitoes’ species encountered in the study location. Similar observation has been reported elsewhere in similar environment²⁴. The presence of these mosquito species is an indication that the environment is conducive for the mosquito development. The higher numbers of C. quinquefasciatus larvae is an indication that the species, which was once considered an urban mosquito is also colonizing rural pockets that were once free of this mosquito¹⁵. However, these observations contradict the report of Emidi et al.²⁵ who reported more Anopheles than Culex mosquitoes in similar experimental environment in Tanzania. The higher density of Culex mosquito than Anopheles affirmed the hypothesis that where Culex mosquito increases, the population of Anopheles mosquito is suppressed³. The population abundance of C. quinquefasciatus in all the breeding sites in this present study is an indication that the changes in the oviposition behaviour of C. quinquefasciatus were necessitated by human population characteristics. The establishment of the Niger Delta University in this study area may not be unconnected with these changes.

Five breeding sites were identified in the study locations. Similar observation has been reported elsewhere²⁶. In all the breeding sites, there was sympatric association between Culex and Anopheles. This observation concurs with the report of Kudom¹⁸, who reported that Anopheles and Culex shows the tendency of co-existence despite the differences in their breeding ecology.

Information on the effect of physico chemical parameter on the mosquito larva productivity is useful in assessing the menace of mosquito borne diseases. In this present study, the physico chemical parameter analyzed were temperature, pH, turbidity, salinity, conductivity, alkalinity and chloride. The breeding sites with higher physico chemical parameters were considered polluted²⁵ Studies have shown that mosquito can breed suitably in a water body whose pH is above 7. However, in this present study, a mean pH of 6.5 was recorded. The pH of 6.5 was slightly lower than 7.07 in Olajiri et al.²⁷, 7.33 in Diana et al.²⁸ and 8.47 in Kipyab et al.²⁹. The abundance of Anopheles mosquito in a breeding site whose PH is slightly acidic (6.5) is an indication that Anopheles is adapting to both polluted and unpolluted water bodies. The adaptability of Culex mosquitoes to both polluted and unpolluted water bodies has been reported⁹.

The mean temperature of mosquito breeding site in this present study ranges between 25.08-28.03°C. The temperature range was comparable with 25.09°C in Olajiri et al.²⁷. A moderately high temperature is said to be suitable to facilitate the growth and development of mosquito larva. The temperature range in this present study was adequate to the larva productivity in all the study locations. Conductivity, turbidity, salinity and chloride in the study location was favorable to the breeding of all mosquito species.

Culex mosquito showed positive correlation with temperature, pH, salinity and chloride. This observation is consistent with Nikookar et al.³⁰ Anopheles mosquito larva showed positive correlation with pH, Temperature and alkalinity. However, the population of Anopheles was significantly influenced by pH. This observation contradicts the report of Kipyab et al.²⁹ who reported that a negative correlation exists between Anopheles and pH, but had a positive correlation with salinity. The correlation between mosquito and physico chemical parameters are said to affect the preferences in the choice of habitats and common food web³⁰. By implication, the physico chemical parameters may have originated from the domestic activities of students in the hostels or from laboratory effluents. Since most part of the school campus is water-log, the effluents are easily circulated. These, have shown enhanced impact on the breeding activities of mosquito in the school campus. Indiscriminate breeding may increase the population of active larva, which can also increase emerge adults. Understanding many of the emerging microhabitat characteristics can thus assist in promoting development of effective control measures against mosquitoes. The adaptability of Anopheles and Culex mosquitoes in the Niger Delta University is an indication that the environment is a foci zone for filariasis. It is recommended that domestic discharge from students’ hostels and laboratory effluents and many other effluents that contains metallic ions that can increase the breeding activities of mosquitoes be properly regulated.

CONCLUSION

It is evident from the study that the predominant mosquito larva recovered from the study location were Culex and Anopheles mosquitoes. Although the two mosquito species showed differences in their breeding ecology, both have shown the tendency of co-existing in the same breeding sites. The breeding characteristics and population abundance of the mosquitoes were influenced by physico chemical parameters such as temperature, humidity, pH, conductivity and turbidity of the water body. The higher population of Culex quinquefasciatus in the study location is an indication that Niger Delta University is a foci zone for Filariasis.

SIGNIFICANCE STATEMENT

This study discovered important information that can be beneficial for the control of mosquito borne parasitic infections in the rural community. Several studies have reported the microhabitat of mosquito species in the rural communities in Bayelsa State. Limited study has shown the relationship between the mosquito breeding site and physico chemical parameter. This study has uncovered the critical role of physico chemical parameter on the breeding preferences of mosquito species. Breeding preferences is the link between mosquito abundance and their chances to make mosquito-man contact. Manipulating the physico chemical parameter of the mosquito breeding site is a milestone to reducing the menace of mosquito-related diseases.

ACKNOWLEDGMENT

We are grateful to our field workers that assisted us in the collection of the mosquito larva. We are also grateful to the staff of the Central Research Laboratory of the Faculty of Science, Niger Delta University for the analyses of the physico chemical parameters.