A Study by
AbdulkadirJamilah Suleiman
DECEMBER, 2001
ABSTRACT
Tbe indoor resting populations of mosquitoes in the Malali, Unguwar Rirni, Tudunwada, Unguwar Sanusi, Kawo, Badiko and Rigasa areas of Kaduna metropolis was surveyed. A total of 380 mosquitoes were collected from seven sampling areas. Two groups of mosquitoes species were encountered. The Culex species constituted99.74% while the Aedes species constituted 0.26% of the total mosquito population caught. The sex ratio (3.7:1) of the mosquitoes favored the females mosqitoes with 78.68%
While the male mosquitoes constituted 21.32% of the total mosquitoes sampled. Hunger States were observed and 5.69% of the female population was hungry with the other 94.31% fed.
INTRODUCTION
Mosquitoes are insects that spread some of the worst diseases of man and animals. Certain kinds of mosquitoes carry the germs that cause such serious diseases as encephalitis, malaria filariasis and yellow fever
Disease- carrying insects have made a major mark on history. Until the use of insecticides during World War II, twice as many people died of insect-borne disease as from fighting (McGavin, 2000).
Malaria is caused by parasiticorganism of the genus Plasmodium. It is essentially a haemo parasite. Mosquitoes of the genus Anopheles are known to transmit human malaria. Malaria is one of the world’s most widespread and severe diseases and it has plagued mankind since prehistoric times (WHO, 1984). McGavin, 2000 reported that malaria kills one human being every twelve seconds.
Also yellow fever is an acute infectious viral disease that is being transmitedbyAedes species. Haematophagus species and Sabethesspecies (Anonymous, 1982).
Filariasis is an infection with roundworms that live in the lymph.
These worms block the flow of the lymph and cause a disease called elephantiasis (Anonymous, 1992). Mosquito, species which serve as vectors of the disease include; Culex, Anopheles, Aedes and Mansonia
Encephalitis is the inflammation of the brain. A large proportion of encephalitis is caused byarboviruses which aretransmitted by mosquitoesand other arthropods. Mosquito species involvedin the transmission of this disease are Aedes and Culex (Anonymous, 1982).
Justification
Understanding the vector biology of mosquitoes or other arthropod vectors will play a major role in the battle against malaria disease. Vector surveillance networks will allow most governments and other agencies to predict outbreaks of disease and to mount effective control efforts.
Aims and Objectives
To determine the occurrence, abundance and distribution of mosquitoes in some areas of Kaduna metropolis
Materials and Methods
The Study Area
The study was conducted in the Kaduna metropolis of Kaduna State,Nigeria.
SamplingSites
Mosquito collections were made from seven wards of the metropolis. Five homes were used in each ward. These wards include;Malali, UnguwarRimi, Tudun Wada, UnguwarSanusi, Kawo, Badiko and
Rigasa
Sampling Method
Resting mosquitoes were collected with an oral aspirator. Each mosquito was covered with the open end of the glass tube and then sucked into the aspirator. Captured mosquitoes were gently blown into labeled paper cups covered with mosquito netting. The mosquitoes were then taken to the laboratory for analysis.
Identification
Chloroform vapor was used to anaesthetize the mosquitoes. Each mosquito was examined under a dissecting microscope and identified rnorphologically into a specific species and sex using taxonomic keys (Gillett, 1972)
Nature of wings was used to identify mosquitos’ species. Mosquitoes having uniformly grayish scales on the wings were identified as Culicines.Aedes species were identified by the banded hind legs.
Nature of antennae was used to identify mosquitoes according to sex. Female mosquitoes were identified by their thread-like (pilose) antennae; Mosquitoes with feathery antennae (plumose) were identified as males.
To establish hunger states, the abdominal appearance of each mosquito was noted. The mosquitoes were then categorized into: unfed, freshly fed,late stage fed, half gravid, sub gravid and gravid accordingto (WHO, 1975),
RESULTS
A total of 380 mosquitoes were caught and identified. Statistical analysis showed a significant difference (p <0.05) in abundance between the different sampling sites. T3 (Tudunwada) had the highest mean number of mosquitoes (25.0) while T4 (UnguwarSanusi) had the least number caught (3.8).
The Culex species constituted the bulk of the population (99.74%), while Aedes species constituted a very minute proportion (0.26%) of the total population.
Figure II is a pie chart showing the composition of the mosquitoessampled. The percentage of female rnoquitoes is 78.68% while that of the male mosquitoes is 21.32%. The sex ratio was found to be 3:7:1
Figure III is a bar chart showing the hunger states of female mosquitoes sampled. 5.69% of the total female population was unfed, while fed females constituted 94.31% of the total number of female mosquitoes caught. Fed females were subdivided into freshly fed (33.69%), late stage fed (30.50%), half gravid (17.38%), sub gravid (5.67%) and gravid (12.77%).
TABLE 1: THE DISTRIBUTION AND RELATIVE ABUNDANCE OF THE MOSQUITOES SAMPLED
T1
|
T2
|
T3
|
T4
|
T5
|
T6
|
T7
| |
NUMBER OF MOSQUITOES SAMPLED
|
5
|
5
|
5
|
5
|
5
|
5
|
5
|
MEAN ( X)
|
13.6a*
|
12.6b
|
25.0abc
|
3.8abc
|
7.0abc
|
7.2abc
|
6.8abc
|
SE ±
|
4.88
|
12.54
|
8.66
|
1.64
|
7.25
|
3.49
|
2.49
|
*Means with the same letters are not significantly different at 5% level of probability as determined by Least Significant Different (LSD)
LSD=4.34
F=19.42
T1 -- Malali
T2 -- UnguwarRimi
T3 -- Tudun Wada
T4 -- UnguwarSanusi
T5 -- Kawo
T6 -- Badiko
T7 -- Rigasa
No. of mosquitoes
FIGURE 3: HUNGER STATES OF THE FEMALE MOSQUITOES SAMPLED
DISCUSSION
There was a high significant difference in abundance of mosquitoes between the different sampling sites .This may be attributed to a number of reasons. From Table 1 sample site T4 had the lowest number of mosquitoes because most of the homes use incense which served as a mosquito repellent. Sample site T3 had the highest number of mosquitoes which is probably due to the availability of alternative resting places provided by hanging clothing. This is in agreement with Service (1976) that the local distribution of adults resting indoors may be affected by the type of construction of houses, the building materials used, the availability of alternative resting places, such as clothing and furniture, and the presence of fires.
Figure 1 explains the species composition of the mosquitoes sampled. Culexspecies made up the bulk of the mosquito population caught, while Aedes species constituted a very small proportion of the population.Polluted water bodies which are favorable breeding sites for Culex species abound in Kaduna metropolis, and this accounted for the high number of Culex species caught in the survey.The deteriorating standards of sanitation, coupled with uncontrolled urbanization and industrialization in Kaduna metropolis have led to an increase in such polluted water bodies.
In this survey, no Anopheles mosquito was caught perhaps due to the small sample size.If the sample size had been larger,the chances of catching an Anopheles mosquito would have been higher.This is in agreement with a previous survey by Ideozu (1987) which produced small numbers of Anopheles species compared to other species.
Figure 2 shows the sex composition ofmosquito sampled. The sex ratio showed that there were about four females for every male. This may be attributed to the fact that males feed on plant substance while females are haematophagous. Therefore it follows that fewer males were found indoors.
In figure 3, the hunger states ofthe female mosquitoes sampled is shown. 5.69% of the female population was unfed while fed females made up 94.3 1% of’ the female population. This is expected because a large proportion of resting females are usually fed.
conclusion
The stated aim of this survey is been achieved. The result shows that Cu!ex species were abundant.
It is worthwhile to note that many problems were encountered duringthe survey due to inaccessibility into homes, and therefore data obtainedare subject to discrepancies. And also because mosquitoes were collected by only one person (the author) thus the relatively fewer number of mosquitoes caught.
Recommendation
Taking into consideration the problems encountered in this survey, more work should be done on the abundance and distribution of mosquitoe’s species.Because data generated will allow for more effective vector surveillance by providing information on vector densities and species composition. This is because vector surveillance is a requirement for vector control.
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