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Effiom, et al: Physico-chemical consideration of
malaria vectors in Ekori, Yakurr LGA of Cross River State, Nigeria
World Journal of Applied Science and Technology, Vol.4. No 2 (2012). 206-217 206
PHYSICO-CHEMICAL ATTRIBUTES OF
MALARIA VECTORS BREEDING SITES
IN EKORI, YAKURR LGA,
CROSS RIVER STATE, NIGERIA
EFFIOM, O. E.1, ALARIBE, A. A. A .2,
USEH, M. F. 2
1Department of Biological Sciences,
Veritas University, Abuja, Nigeria.
2Department of Medical Microbiology/Parasitology,
University of Calabar, Calabar, Nigeria.
e-mail: effiomo@veritas.edu.ng
ABSTRACT: This research aimed to investigate the physico-chemical
parameters of various mosquito-breeding sites in Ekori, Cross River State,
Nigeria. Knowledge of physico-chemical factors that influence mosquito
breeding could be useful in mosquito population control. Larvae of
mosquitoes were collected fortnightly from 28 breeding sites, and identified
into anophelines and culicines. Similarly, water samples were collected from
the same breeding sites and analyzed for physico-chemical parameters such
as carbonate, bicarbonate, chlorine, dissolved oxygen, carbondioxide, pH,
conductivity, etc. Water depth and temperatures were measured together
with the survey of the physical surroundings, nature and conditions of the
sites. The monthly rainfall of the study area was measured. The values of
these parameters for the different mosquito habitats showed variation
between the dry and the rainy seasons. Variable abundance of mosquito
larvae and two species of malaria vectors in the respective habitats were also
observed. These findings could be attributed to the corresponding variability
observed in the values of physico-chemical parameters of the habitats. High
populations of anopheline larvae were found in the breeding sites that had
warm temperature (28-300C), clean shallow waters, high concentration of
HCO3-, CO32-, DO, low concentrations of NO3,- low numbers of larvivorous
organisms as well as the presence of water lettuce vegetation either within or
around the habitats. Correlation analysis of the relation between physico-
chemical parameters and mosquito larval abundance showed significance (P
< 0.05). The results of this study suggest that physico-chemical parameters
of mosquito breeding sites can be manipulated to check mosquito larval
abundance for effective malaria control.
INTRODUCTION
The link between malaria and water has from time immemorial been an unbreakable one,
especially as the life cycle of mosquito is entirely water-dependent, and mosquitoes are getting
easily adapted to various water conditions in propagating themselves. The diverse water quality
used by various Anopheles mosquitoes to breed and propagate themselves may be temporary
(or transient), permanent, natural or man-made (Bourne, 2003; MAC 2003; NJMCA 2003). A
good number of ecological factors influence the choice of site for breeding or oviposition as
well as abundance of different species of anophelines. One very important ingredient for
successful production of aquatic life forms is a proper balance of physical, chemical and
biological parameters of water in ponds, lakes and reservoirs (Mustapha and Omotosho, 2005).
Also, the interaction of both the physical and chemical properties of water influences the
composition, distribution and abundance of aquatic organisms. The presence or absence of
chemical elements in water body might be a limiting factor in the aquatic life productivity of
ISSN: 2141
–
3290
Effiom, et al: Physico-chemical consideration of
malaria vectors in Ekori, Yakurr LGA of Cross River State, Nigeria
World Journal of Applied Science and Technology, Vol.4. No 2 (2012). 206-217 207
such water body could determine the types of organism that may be available. Besides, it may
indicate ecologically unstable ecosystem which can have positive or negative impact on the
population of aquatic diversity (Pasche, 1980; Williams 1990; Sidneit et al., 1992; Despommier
et al., 2000). Mustapha and Omotosho (2005), in their assessment of the physico-chemical
properties of Moro Lake in Kwara State, Nigeria, reported how human agricultural activities
sufficiently altered the physico-chemical characteristics of a natural fresh water body and also
the natural dynamics which adversely affect other parameters such as aesthetics of the water,
species distribution and diversity, their production capacity, and even disruption of the
ecosystem balance in the water
Previous studies have revealed direct correlation between the availability of water and the
frequency in which mosquito breeds and feeds on humans (Despommier et al., 2000). This
invariably implies that environmental factors directly and indirectly influence malaria
transmission through their impact on the vectors. In other words, every physical and chemical
environmental change in the mosquito habitat, be it natural or man-made, will re-orient the
ecological landscape in which these vectors breed (Despommier and Chen 2003). The
environmental factors that are said to impact on the malaria vectors and thus influence malaria
transmission are changes in temperature, humidity, altitude, human population density,
deforestation, farming, spread of irrigation project, and physico-chemical parameters (such as
dissolved oxygen, carbon dioxide, carbonates, bicarbonates, nitrates, sodium chloride, chlorine,
turbidity, conductivity, water depth, pH, etc.).
This study investigates the physico-chemical properties of the breeding and oviposition sites of
malaria vectors in Ekori, Yakurr Local Government Area of Cross River State, Nigeria and
their influence on the mosquito larval abundance.
MATERIALS AND METHODS
Study Area
The study site is located in Ekori, a sub-urban settlement centrally located in Yakurr Local
Government Area of Cross River State, Nigeria. It is situated between latitude 4o 27’ and 6o 56’
North and longitude 7o 51’ and 9o 29’ East in the globe, and is about 135 km from Calabar, the
State capital. It is one of the largest native communities in Cross River State, with a
homogenous population of over 350,000 people. The community is surrounded by tropical rain
forests with pockets of swamps and undeveloped plots of land overgrown with weeds and
bushes within the town, all of which provide convenient hideouts and breeding sites for
mosquitoes, the vectors of malaria, yellow fever, filariasis, etc. The six months study was
undertaken between the months of February and July in 2010.
Parasitological Field Survey
During the field survey, mosquito larvae were collected fortnightly (early and late month) from
deep streams. Also two batches (28 each batch) of water samples were collected in February
and July, respectively, from various breeding sites for physico-chemical analyses. Both
temperature and depth of the water were also measured on site. The water samples were
analyzed in the Oceanography Departmental Laboratory of the University of Calabar, Calabar.
The amount of monthly rainfall in the area was measured. Statistical analyses were carried out
to determine the relationship between physico-chemical properties and the larval population.
Collection of Larvae and Pupae of Mosquitoes
The dipper tool method described by WHO (1992a) and WHO (1992b) was used to collect
larvae and pupae of mosquitoes in deep wells and streams. The improvised dipper tool was
gently lowered into the water at an angle of 45⁰, such that only one side is below the water
surface, and was used to cautiously skim along the water of the breeding sites, after which it
Effiom, et al: Physico-chemical consideration of
malaria vectors in Ekori, Yakurr LGA of Cross River State, Nigeria
World Journal of Applied Science and Technology, Vol.4. No 2 (2012). 206-217 208
was lifted up making sure that the water in it with the larvae and pupae did not pour out. With
the aid of a dropper, they were sucked into the preservative. The skimming was repeated after
the disturbed water had settled down and the larvae and pupae came up to the surface again.
Collections from well were carried out still with a dipper tool whose handle had been extended
by tying a long stick to it. In water bodies covered with floating vegetation, the vegetation or
debris were first cleared with the dipper tool before collecting the larvae and pupae as described
above.
Mosquito Larvae Identification
Morphometric identification methods of Gilles and Meillon (1968), Ribeiro and Ramos (2003)
were used to identify the larvae. The anophelines showed the absence of breeding tube (siphon)
at the last abdominal segment, possession of median tergal plates with a pair of palmate or
“float” hairs on the 1st - 8th abdominal segment and only a pair of the thorax, and the presence
of laterally placed tufts of spines called pecten on the 8th abdominal segment.
The larvae of the two identified Anopheles species were distinguished from each other by the
possession of three types of anopheline larval hairs, namely the shoulder, mesopleural and
palmate hairs. There were sutural hair and absence of pigmentation on the clypeus (of
Anopheles gambiae). While Anopheles funestus possessed four types of anopheline larval hairs,
the shoulder, mesopleural, palmate and sutural hairs, and two distinct transverse bands of dark
colour on the clypeus.
Determination of Physico-chemical Parameters of Water Samples from the Breeding Sites
Twenty eight (i.e., 2 sets of 14) water samples collected from mosquito breeding sites in the
study area and labeled appropriately were analyzed for dissolved oxygen, carbon dioxide,
temperature, pH, conductivity, turbidity, depth and metals using Dissolved Oxygen Kit,
Mercury Thermometer, pH meter, Conductivity meter, sacki disc, and Atomic Absorption
Spectrophotometer (for metals) respectively.
Measurement of Rainfall
Fourteen improvised rain gauges were constructed from measuring cylinders (plastic), funnel
(plastic), mosquito net and black paper (Ramlingam et al., 1977). The net played the role of
filter while the black paper was used to check evaporation of the water already in the cylinder.
In each village, the set-up was strategically placed undisturbed place where rain water can
collect in it. A supervisor living around the place was appointed to monitor it. Readings were
taken on the last day of every month for six months.
Statistical Analyses
The various data gathered during the study were subjected to statistical analysis using T-test to
compare seasonal variations as well as equality of means, and Pearson correlation to compare
physico-chemical parameters with larval population.
RESULTS
Mosquito larvae (7,247) were collected from the 28 breeding sites during the 6-months study.
Of this, 652 (9.0%) were anophelines while the rest 6,595 (91.0%) were culicine larvae. Of the
652 anopheline larvae, 167 (25.61%) were identified as An. funestus and the other 485
(74.39%) were An. gambiae sensu strict .
Effiom, et al: Physico-chemical consideration of
malaria vectors in Ekori, Yakurr LGA of Cross River State, Nigeria
World Journal of Applied Science and Technology, Vol.4. No 2 (2012). 206-217 209
Fig 1a: The different breeding sites, their physical conditions, the types and numbers of mosquito larvae caught per month during dry season.
Effiom, et al: Physico-chemical consideration of
malaria vectors in Ekori, Yakurr LGA of Cross River State, Nigeria
World Journal of Applied Science and Technology, Vol.4. No 2 (2012). 206-217 210
Fig 1b: The different breeding sites, their physical conditions, the types and numbers of mosquito larvae caught per month during rainy season.
Effiom, et al: Physico-chemical consideration of
malaria vectors in Ekori, Yakurr LGA of Cross River State, Nigeria
World Journal of Applied Science and Technology, Vol.4. No 2 (2012). 206-217 211
Tables 1a and 1b present the types of the breeding sites surveyed during study period, their true physical
appearances, the types of mosquito larvae and their total numbers per month per village each month
Figure 2: Summary of monthly larvae collections for the six months study period
Figure 2 depicts the percentage representation of the monthly distribution of mosquito larvae collected
from February to July, and it shows that for anophelines, only 2 (0.3%) were caught in February, 18
(2.76%) in March, 46 (7.60%) in April, 168 (25.76%) in May, 298 (45.71%) in June, and in July 120
(18.40%). High collections started in the month of May, with a peak in June, and dropped drastically in
July (Figure 1). In the monthly summary of culicine caught, February had a total of 1,019 (15.44%),
March had 572 (8.67%), April had 610 (9.25%), May had 999 (15.15%) larvae, June and July, 2,545
(38.59%) and 850 (12.89%) larvae, respectively. May and June had the highest numbers of larvae.
No. of each Anophelines/Culirimes caught (in %)
120
100
80
60
40
20
2
3.1
7.1
14.4
10.5
12.4
99.8
91.9
92.9
85.6
89.5
87.6
February
March
April
May
June July
Effiom, et al: Physico-chemical consideration of
malaria vectors in Ekori, Yakurr LGA of Cross River State, Nigeria
World Journal of Applied Science and Technology, Vol.4. No 2 (2012). 206-217 212
Table 2: Seasonal mosquito larvae collections per village per village (Dry and Rainy seasons)
VILLAGE
SEASONAL
COLLECTION
GRAND TOTAL
DRY SEASON RAINY
SEASON
FEB.
MARCH
APRIL
TOTAL
MAY
JUNE
JULY
TOTAL
LEKPANKOM (LE) 0 33 74 107 2 130 466 598 705
AKUGOM-EBE (AK) 2 61 84 147 88 85 492 665 812
EPENT
I
6
49
35
90
400
94
100
594
384
(EP)
AFREKPE 5 86 60 151 0 175 108 283 434
(AF)
EPENTI BEACH 5 93 13 111 120 73 24 217 328
(EB)
OKONOBONGHA
(OK)
0
82
79
161
59
157
103
319
480
EDANG(ED) 0 58 86 144 0 192 163 355 499
AKUGOM-NKPATU (AN) 3 68 73 144 54 138 93 285 429
AJERE
0
70
78
148
0
148
142
290
438
(AJ)
AJERE-BEACH (AB) 6 45 57 108 62 109 128 299 407
KEKOMKOLO
(KK)
0
80
50
130
0
193
102
295
425
NTAN (NT) 0 55 87 142 0 187 218 405 547
NTAMKPO-NTAN (NN) 12 116 32 160 128 64 38 230 390
NEW EKORI
(NE)
0
34
92
126
0
134
709
843
969
TOTAL 39
(2.1) 930
(50.8) 900
(49.2) 1873 (25.8) 613
(11.4) 1879 (39.5) 2886 (39.8) 5678
(78.3) 7247
Effiom, et al: Physico-chemical consideration of
malaria vectors in Ekori, Yakurr LGA of Cross River State, Nigeria
World Journal of Applied Science and Technology, Vol.4. No 2 (2012). 206-217 213
In terms of the two seasons, that is, dry season (February to early April) and Rainy season (late
April to July), a total of 1,869 (25.79%) larvae were collected in the dry season. Of this
number, only 39 (2.09%) were anopheline (i.e. 14 (35.90%) An. funestus and 25 (64.10%) An.
gambiae). Culicines dominated with 1,830 (97.91%).
Table 3: Distribution of adult anopheles species in the study area
VILLAGE MALE ANOPHELES FEMALE ANOPHELES
gambiae funestus Total gambiae funestus Total
LEKPANKOM (LE) 4 2 6 21 3 24
AKUGOM-EBE (AK) 5 1 6 17 1 18
EPENTI (EP) 5 2 7 16 4 20
AFREPE (AF) 2 0 2 18 4 22
EPENTI BEACH (EB) 4 1 5 15 0 15
OKONOBONGHA (OK) 5 1 6 14 3 17
EDANG (ED) 3 0 3 13 2 15
AKUGOM-NKPATU (AN) 6 0 6 19 1 20
AJERE (AJ) 6 1 7 1 2 13
AJERE-BEACH (AB) 5 0 5 22 0 22
KEKOMKOLO (KK) 6 0 6 11 1 12
NTAN (NT) 6 1 7 13 2 15
NTAMKPO NTAN (NN) 7 2 9 1 5 16
NEW EKORI (NE) 5 0 5 23 2 25
TOTAL 69 11 80 224 30 254
Besides the numbers of each species of Anopheles mosquito larvae collected during the study,
Table 3 also gives the sexes and their numbers. The rainy season collections on the other
hand, recorded 5,678 (78.3%) larvae out of which 613 (11.39%) were anophelines, i.e., 153
(24.96%) An. funestus and 460 (75.04%) An. gambiae), and 4,765 (88.61%) were culicines.
Tables 4a and 4b depict the variable values of physico-chemical parameters of the various
mosquito breeding sites in Ekori, taken during the dry and rainy seasons of the study period.
Variations were observed between the physico-chemical parameters of water samples obtained
during the dry season and those of the rainy season. For example, the pH, which was lightly
alkaline in the water samples of the dry season, became completely alkaline in those obtained
during the rainy season. Similarly, the values of DO varied with the seasons and locations of
the breeding sites. Other parameters like nitrate, phosphate, chloride, etc., though they were
under tolerable limit also fluctuated widely according to seasons and site locations. High levels
of DO were observed mostly in water samples collected during the rainy season, and could
probably be due to absence of pollutants in those sites where weeds were present and their
photosynthetic activities had helped to aerate the water. Polluted sites on the other hand showed
less DO and high CO2 values. The most common contaminants found in some habitats during
this study were agricultural pesticides, laundry detergents, oils and other petroleum products,
and all the habitats with these pollutants had very scanty numbers of mosquito larvae. Some
larvivorous organisms such as water spiders, water boatman and other forms of water insects
and fish fries were also observed in some habitats during this study.
Effiom, et al: Physico-chemical consideration of
malaria vectors in Ekori, Yakurr LGA of Cross River State, Nigeria
World Journal of Applied Science and Technology, Vol.4. No 2 (2012). 206-217 214
Table 4a: Physico-chemical properties of the water samples collected in February
(the peak of dry season) from the mosquito breeding/oviposition sites
Village Physico-chemical measurements for Dry season (February)
HCO
3
- Cl- NO3-
N DO CO
2
pH Cond. CO
3
2- Turb. Temp. Depth
mg/l mg/l mg/l mg/l mg/l pH µs/cm mg/l FTU ⁰C M
LE 54.9 290 2.5 2.5 0 6.5 806 35.1 0 29.6 0.3
85.4 258.7 1.4 4 0 6.3 719 54.6 27 23 0.3
AK 170.9 682.2 1.3 4.2 0 6.7 1896 109.1 57 20.2 0.3
97.6 381 2.1 3.6 1 7.2 106 62.2 17 41.3 0.1
EP 12.2 30.9 1.4 4 1.5 6.8 86.3 7.8 5 18.5 0.2
30.5 34.7 1.9 1.4 1 7.2 152 19.5 10 20.4 0.3
AF 13.3 34.3 1.3 3.7 1.6 6.7 93.4 8.4 5 18.8 0.3
29.6 30.6 1.8 1.6 1.1 7.8 163 17.8 12 24.2 0.5
EB 18.2 76.6 2.9 1 1 7.2 213 11.7 22 19.6 1.6
24.4 38.9 2.6 1.7 0 6.5 108 15.6 24 23.8 0.3
OK 36.4 45.2 1.9 1.8 1.5 6.7 75.2 12.8 18 26.2 0.3
45.3 36 2.8 2.6 1 7.3 672 48.7 14 20.3 1.3
ED 24.4 41.4 1.9 3.7 1 6.7 115 18.6 89 25.2 0.5
48.8 90.3 2.6 2.5 1 7.2 251 31.2 22 38.6 0.2
AN 79.3 33 1.8 4.2 0 7 918 50.7 36 23.6 0.2
24.9 201.8 1.8 3 0 6.9 561 15.6 18 28.7 0.3
AJ 61 169.4 2.8 0.8 0 7.4 471 89 21 31.6 0.1
79.3 263 2.1 3.8 1 6.1 731 50.7 15 19.4 1.2
AB 18.3 42.4 1.4 3.3 2 6.9 118 11.7 40.7 16.9 1
48.8 112.2 1.9 1.5 1.5 6.8 312 31.2 84 20.1 1.3
NT 73.2 110.4 2.2 1.6 1 7.1 307 46.8 44 24.1 0.2
183 561.6 2 0.4 1.5 6.8 156 117 49.4 19.2 0.2
NN 36.6 83.1 1.2 1.6 1 6.8 231 23.4 75 27.4 0.2
78.8 92.8 2.4 3.3 1 7.1 258 31.2 4 21.6 0.2
KK 36.6 225 1.7 3.8 1 7 625 23.4 5 26.4 0.3
48.4 225.2 1.3 3.8 0 7.4 626 31.2 10 23.5 0.4
NE 146.4 320.2 1.3 0.6 0 7.1 890 93.6 89 27.6 0.9
18.3 27.4 1.3 3.6 3.3 7.8 76.3 11.7 10 31.7 0
DISCUSSION
This study has shown that different water bodies including even domestic drinking water in
pots (clay or plastic types) constitute the common temporary and permanent breeding sites for
mosquitoes in the area, from which 7,247 mosquito larvae were caught. In line with the
observed seasonal variations in the physcico-chemical parameters of the mosquito breeding
sites, there was a corresponding variation in the mosquito larvae abundance as well as mosquito
species in the various sites. Thus, normal DO favoured anopheline mosquito larvae abundance
while low levels of DO enhanced the abundance of culicine mosquito larvae which do not
normally discriminate against breeding sites because they have the capacity to breed even in
habitats with very harsh conditions. The influence of fluctuating physico-chemical parameters
Effiom, et al: Physico-chemical consideration of
malaria vectors in Ekori, Yakurr LGA of Cross River State, Nigeria
World Journal of Applied Science and Technology, Vol.4. No 2 (2012). 206-217 215
on the mosquito larval abundance has confirmed the findings of Patra et al., (2010) on the
seasonal variation in physico-chemical parameters of chilika Lake in India.
Table 4b: Result of Physico-chemical measurements of the water samples collected in February
(the peak of dry season) the mosquito breeding/oviposition sites
Village Physico-chemical measurements for Dry season (February)
HCO
3
- Cl- NO
3
-N DO CO
2
pH Cond. CO
3
2- Turb. Temp. Depth
mg/l mg/l mg/l mg/l mg/l pH µs/cm mg/l FTU ⁰C M
LE 51.7 280 2.6 3.6 1 7.5 810 35.6 0 19.4 0.5
82.3 248.4 1.4 5.8 0.2 7.7 717 55.2 28 16.4 0.4
AK 161.8 598.2 1.3 5.6 0.1 5.8 1899 110.8 56.2 19.2 0.5
113.2 292.6 2 4.7 1.8 7.6 24 63.8 16 20.4 0.3
EP 18.6 31.8 1.8 5.1 1.6 7.4 88.6 8.2 4 16.2 0.5
26.4 32.7 1.3 2.1 1.5 7.6 154.2 20.5 8 17.3 0.6
AF 14.4 33.8 1.4 4.2 1.9 7.7 95.3 9.3 4 15.7 0.5
27.3 28.6 3.6 2.5 1.4 7 164.3 16.7 10 19.4 0.4
EB 17.3 722.3 2.9 2.2 1.2 7.1 214 11.5 21 16.1 2.1
26.4 36.6 1.7 1.9 0 6.8 110 16.6 22 19.8 0.5
OK 34.5 50.1 2.8 1.9 1.7 6.9 76.8 12.4 11 21.6 0.5
43.8 36.7 1.7 2.3 1.5 7.5 675 60.5 13 17.3 1.9
ED 26.3 40.6 2.5 4.2 1.6 7 125 17.4 79 21.3 0.3
49.9 89.4 1.4 2.8 1.3 7.8 255 32.1 13 18.1 0.4
AN 78.4 35 1.6 4.7 0 7.1 921 51.5 28 19.6 0.5
26.1 202.8 2.7 3.6 0 7 563 18.2 16 23.4 0.4
AJ 63 169.9 2.1 1.2 1 7.6 474 39.8 17 25.1 0.1
79.9 263.8 1.2 4.3 1.2 6.8 735 52.6 12 14.7 1.8
AB 20 38.4 2 3.7 1.6 6.9 120 11.9 39.6 15.3 1.5
48.6 113.4 2.2 2 2.1 7.7 316 33 18 19.4 0.5
NT 75 108.3 2.1 1.8 2.2 7.5 310 48.9 40 21.2 0.4
183.5 551.9 1.3 1 2 7 150 118.1 49.3 14.6 0.6
NN 37.8 82.8 2.5 1.9 5.4 7.2 232.3 25.6 71 20.1 0.5
79.6 90.8 2 4.7 5.5 7.4 259 34.4 2.5 16.5 0.6
KK 37.8 222.2 1.4 4.5 1.7 7.1 626 25.7 3 22.1 0.6
48.8 224.1 1.5 4.6 0 7.6 627.2 33.1 7 19.8 0.6
NE 146.2 330.2 1.6 1.4 0 7 902 90.2 88 22.6 0.5
18.9 26.5 2 4.2 2.6 6.2 78.1 11.9 6.2 27.4 0.1
It could also be suggested that the same impact may have been made by fluctuations in the
levels of temperature, carbonate (CO32-), bicarbonate (HCO3-) pH, nitrate ion (NO3-), chlorine
ion, and turbidity and the depth of water, as well as by the presence or absence of vegetation
cover, thereby resulting in the variation of mosquito larval densities in the different breeding
sites. Compared to the culicines, the anopheline mosquito larval densities generally tended to
be relatively low in habitats that showed low DO perhaps due to pollution, except in fresh and
clean water habitats such as ponds with vegetation cover, streams, springs, cisterns, and clean
river banks and drinking water in pots. This implies that the abundance and types (or species)
of mosquito larvae in a given habitat depend to some extent upon the type of habitat, location,
dissolved constituents and other environmental attributes such as presence and absence of
Effiom, et al: Physico-chemical consideration of
malaria vectors in Ekori, Yakurr LGA of Cross River State, Nigeria
World Journal of Applied Science and Technology, Vol.4. No 2 (2012). 206-217 216
vegetation cover within and around the habitats. Similar observations have been reported by
Mustapha and Omotosho (2005) in their study of the physico-chemical properties of Moro
Lake in Kwara State, Nigeria. However, the observed influence of physico-chemical and
biological parameters on the mosquito larval density and the intra-stream variation of the larval
abundance of anopheline species (An. gambiae s.s complex and An. funestus) which also
resulted from physical and vegetational variability of the habitats, have both agreed with the
findings of Overgaard et al., (2003) on the characteristics of An. minimus (Diptera: Culicidae)
larval habitats in Northern Thailand, and those of Robert et al. (1998) on the ecology of An.
arabiensis (Diplera: Culicidae) in the market Garden wells in Urban Dakar, Senegal.
Statistical Analysis of the relation between physico-chemical parameters and mosquito larval
abundance showed significance (P < 0.05). It was also found that the high abundance of the two
species of anopheles (An. gambiae and An. funestus) in Ekori, were favoured by water bodies
that had warm temperature (between 28 and 30⁰C); clean and clear shallow waters with high
DO content, low concentration of NO3- and CL-; and presence of water lettuce vegetation
within or around the habitat (WHO, 1992a). Correspondingly, breeding sites or habitat with
physico-chemical and biological measurements contrary to those mentioned above may have
impaired oviposition, development and survival of the gravid female mosquitoes generally, as
in the case of anophelines, hence, low density of anopheline mosquito larvae.
The low mosquito larvae density observed in habitats polluted with agricultural pesticides,
laundry detergents, oils and other petroleum products, thick canopy of vegetation cover could
be attributed to the presence of these contaminants. The later may have altered the aesthetics of
the habitats thereby making it unfavorable for successful oviposition by gravid females. This
finding has agreed with earlier reports by Allan (1995), Teng et al. (1998) and Murihead-
Thomson (1940a) who explained pollutants such as those mentioned above, and thick canopy
constitute a limiting factor for mosquito larvae abundance.
However, a t-test analysis to compare the influence of seasonal variations on the available
mosquito species and larval population generally, proved significant (P < 0.05). The result of
these analyses showed that seasonal fluctuations in the physico-chemical parameters of the
breeding sites were significant enough to bring about observable variations in the larvae
abundance either within or between seasons. This may be true because in the month of March,
for instance, a drastic drop in larval density was observed perhaps due to the drying up of some
breeding sites following absence of rain. The presence of larvivorous organisms in some
mosquito habitats may have equally contributed to the low mosquito larval densities recorded
in those habitats.
CONCLUSION
Besides identifying the different mosquito breeding sites in the area and their physical,
chemical and biological conditions, this study has also, established the effect of biophysico-
chemical parameters on mosquito larval population or density, as well as on the mosquito
species (Anopheles gambiae and Anopheles funestus) transmitting malaria in Ekori.
ACKNOWLEDGEMENT
Our gratitude to the Clan Head of Epenti and Obol Denis Onen David, his Council of Chiefs
and the youths of the community.
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Hall, London
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