Studies on Some Biological and Physicochemical Parameters of Rock Pool Habitats of Mosquitoes (Diptera: Culicidae)
Chapter One
Aim of the Study
To evaluate the biological and physicochemical contents of rock pool breeding habitats of mosquitoes in Kaduna State, Northern Nigeria.
Objectives
- To determine the species composition and relative abundance of mosquito breeding in rock pool habitats in Kaduna
- To determine the biota composition of rock pools link with the breeding of Mosquitoes
- To determine the physicochemical parameters of rock pools.
CHAPTER TWO
LITERATURE REVIEW
Overview of Mosquito Species
There are some 3300 species of mosquitoes belonging to 41 genera, all belongingin the family Culicidae. This family is divided into three subfamilies: Toxorhynchitinae, Anophelinae (anophelines) and Culicinae (culicines). Mosquitoes have a worldwide distribution. They occur throughout thetropical and temperate regions and extend their range northwards intothe Arctic Circle. The only areas from which they are absent are Antarctica,and a few islands. They are found at elevations of 5500mand down minesat depths of 1250m below sea level.The most important pest and vector species belong to the genera Anopheles,Culex, Aedes, Mansonia, Ochlerotatus, Psorophora,Haemagogus and Sabethes.Anopheles species, as well as transmitting malaria, are vectors of filariasis(caused by Wuchereria bancrofti, Brugia malayi and Brugia timori) and a fewarboviruses. Certain Culex species transmit W. bancrofti and a varietyof arboviruses. Aedes species are important vectors of yellow fever,dengue, encephalitis viruses and many other arboviruses, and in a fewrestricted areas they are also vectors of
- bancrofti and B. malayi. Species in the very closely related genus Ochlerotatus also transmit filariasis and encephalitis viruses. Mansonia species transmit B. malayi an d sometimes W. bancrofti and a few arboviruses. Haemagogus and Sabethes mosquitoe s are vectors of yellow fever and a few other arboviruses in Central and South America, while the genus Psorophora contains some troublesome pest species in North and Sout h Americaas well as a few transmitting arboviruses (Service, 1997).
- External morphology of mosquitoes
Mosquitoes possess only one pair of functional wings, the fore-wings. The hind-wings are represented by a pair of small, knob-like halteres. Mosquitoes are distinguished from other flies of a somewhat similar shape and size by: (1) the possession of a conspicuous forward projecting proboscis;(2) the presence of numerous appressed scales on the thorax, legs, abdomen and wing veins; and (3) a fringe of scales along the posterior margin of the wings. Mosquitoes are slender and relatively small insects, usually measuring about 3–6 mm in length. Some species, however, can be as small as 2 mm while others may be as long as 19 mm. The body is distinctly divided intoa head, thorax and abdomen. The head has a conspicuous pair of kidney-shaped compound eyes. Between the eyes arises a pair of filamentous and segmented antennae. In females, the antennae have whorls of short hairs (that is pilose antennae),but in males, with a few exceptions in genera of no medical importance, the antennae have many long hairs giving them a feathery or plumose appearance. Mosquitoes can thus be conveniently sexed by examination of the antennae: individuals with feathery antennae are males, whereas those with only short and rather inconspicuous antennal hairs are females (Service, 1997).
Just below the antennae is a pair of palps which maybe longor short and dilated or pointed at their tips, depending on the sex of theadults and whether they are anophelines or culicines. Arisingbetween the palps is the single elogated proboscis, which contains the piercing mouthparts of the mosquito. In mosquitoes the proboscis ch aracteristically projects forwards. The thorax is covered, dorsally and laterally, with scales which may bedull or shiny, white, brown, black or almost any colour. It is the arrangementof black and white, or coloured scales on the dorsal surface of thethorax that gives many species (especially those of the genera Aedes andOchlerotatus) distinctive patterns.The wings of mosquitoes are long and relatively narrow, and the number and arrangementof wing veins is virtually the same for all mosquito species.
The veins are covered with scales which are usually brown, black, white or creamy yellow, but more brightly coloured scales may occasionally be present. The shape of the sc ales and the pattern they form differ considerably between both genera and species of mosquitoes. Scales also project as a fringe along the posterior border of the wings. In life the wings of resting mosquitoes are placed across each other over the abdomen in the fashion of a closed pair of scissors. The legs of mosquitoes are long and slender and are covered with scales which are usually brown, black or white and may be arranged in patterns, often in the form of rings (Service, 1997).
CHAPTER THREE
MATERIALS AND METHODS
Study Area and Sites
This study was carried out on theexotic plateaux and rocky hills ofKaduna State located between (Lat 8°30’0”N and 11°30’0’N) and (Long 6°0’0’E and 8°30’0”E), Northern Nigeria. Vegetation type comprises tropical grassland in the southernGuinea Savannah to Sudan Savannah (NACD, 2013). Rainfall is heavy in the southern part and around Zaria in the northern part; with average rainfall of about 1016mm (NACD, 2013). The State enjoys a rainy season of about five (5) months. Available rock pools sampled for mosquito breeding were spatially distributed in 21 settlements endowed with inselbergs. Sampling locations is made up of seven (7) Local Government Areas out of the23 in the state. The southern Guinea Savannaharea comprise: Jaba, Jema‟a, Kachia, Kagarko, Kaura, Sanga and Zango-Kataf,Birnin-Gwari (partly Guinea Savanna and partly Sudan Savannah), Chikun, Igabi, Lere, Kaduna- North, Kaduna-South, Kajuru, Kauru, whilst the Sudan Savannah areas are: Kubau, Kudan, Makarfi, Ikara, Giwa,Zaria, Sabon-gari and Soba. Jere, Kagarko (Kagarko L.G.A.), Kwoi, Nok, Chori, Samban-Gida (Jaba L.G.A.) and Kagoma (Jema‟a L.G.A.), Kangimi (Igabi L.G.A.), Malali (Kaduna-North L.G.A.), Baban-Sora, Kujama (Kajuru L.G.A.), Kajuru, Tudun- Mare and Kufana (Kajuru L.G.A.) settlements were sampled in Guinea Savannah. Hanwa (Sabon-Gari L.G.A.), Danmagaji, Wusasa, Kufena, Dutsen-Abba, Dumbi and Zango-Aya (all in Zaria L.G.A) settlements were sampled in Sudan Savannah.
Parts of the State like Zaria, Kagoro and Kwoi areas have protruding hard resistant granite rocks result out due to weathering through the ages of previous existing pre- Cambrian rocks. The erosive activities resulted in the outgrowth of rocks forming inselbergs and large rocky upland regions(NACD, 2013).The undulating plateaux possess several depressions in which rainwater collects to form discrete pools during the rainy season. These collections of water serve as effective breeding habitats for mosquitoes. The State occupies part of the central position of the northern part of Nigeria (with Kaduna as its capital) and shares common borders with Zamfara, Katsina, Niger, Kano, Bauchi and Plateau states. To the South-West, the state shares a border with the Federal Capital Territory, Abuja. Kaduna State is the fourth most populous state in the federation and represents a major focus and centre of political and economic activities in the nation.The State occupies an area of approximately 48,473.2 square kilometers and has a population of 6,113,503 and a population density of 130 people per square kilometre. It accounts for 4.3% of Nigeria‟s total population(NPC, 2006). There are two marked seasons in the State, a dry windy season and a rainy (wet) season. The wet season is usually from April through October with great variations as onemove northwards.The two climatic conditions (wet and dry) in the state greatly influence activities of the people, who are predominantly engaged in agriculture.
CHAPTER FOUR
RESULTS
A total of 386 rock pools distributed in 21 settlements on several inselbergs at heights ranging from 597m to 811m above sea levelwere examined for larval stages of mosquito (Table 4.1). A total of 31,726 mosquito larvae were collected from 269(69.7%) rock pools.These ranged from 6 pools on Kufana inselbergs to 37 pools on Zango-Aya inselbergs. The numbers of pools examined were reflective of their relative availability on the inselbergs during the rainy season. Malali inselberg had the highest (100%) percentage larval positivity and was among the inselbergs encounterd with least number of pools. The highest numbers (37) of pools was observed on Zango-Aya inselberg, with(67.6%) larval positivity. The least number of pools (6) was observed on Kufana inselberg, without larval mosquito (0%). The least (31.8%)larval positivitywas observed on Dutsen-Abba inselbergs. The highest number of larvae (5,042) was collected from Hanwa,inselberg while the least (242) was collected from Nok inselberg. The relative abundance of larvae was highest (701.7) on Wusasa inselberg which also had the highest larval density(526.3) per pool while the least (29.5)larval abundance was observed on Tudun-Mare inselberg. Kujama inselberg was the tallest at (76m)while Kangimi inselberg had the least 4m height amongst the inselbergs studied.
Eight species of mosquito larvae distributed in three genera (Aedes, Anopheles, Culex) which includedAe. vittatus, An. arabiensis, An. gambiaes.l., An. gambiae s.s., An. longipalpis, Culex perfidiosus, Cx. pipiens pipiens and Cx. simpsoni bred in rock pools in northern part of the State (Table 4.2).
CHAPTER FIVE
DISCUSSION
In this study, rock pools constitute breeding microhabitats to the three main genera (Anopheles, Aedes and Culex) of mosquito vectors responsible for the worst scourges of humankind. The physicochemical and biological factors determining theproliferation of mosquitoes in rock pool habitats were elucidated in this study. This study therefore provides information on the spatial distribution and ecology of preimaginal stages of mosquitoes in the relatively accessible patchy rock pool habitats as influenced by species assemblages of freshwater invertebrates, vertebrates and aquatic macrophytes. The abundance of the organisms was reflective of the durational instability (disappearance and appearance) of the pools during the rainy season. Rock pools are maintained exclusively by rain which within 3 to 4 days becomes effective breeding habitats for mosquitoes. However, rain seizure during the preliminary stage of this work left some of the pools on the rocks with freshly filled rainwater without mosquito larva. This was evident on Danmagaji and Kufena inselbergs which recorded relatively low abundance of mosquito larvae amongst other inselbergs sampled for mosquito breeding in parts of Kaduna North. Similarly,rainless (break) period towards June ending may have accounted for the low volume or absence of waters in majority of rock pools and invariably the low population or absence of mosquito larvae particularly. This could be the cause of the negativity in the abundance of mosquito larvae on the Kufana inselberg in the central part of Kaduna state. Since rock pools communities are completely dependent on length and frequency of inundations, the active community reflects the prevailing weather conditions (Jocque et al., 2010).
CHAPTER SIX
CONCLUSION AND RECOMMENDATIONS
Conclusion
This study has documented the occurrence and abundance of thirteen species of mosquito larvae (Ae. vittatus, An. arabiensis, An. gambiae s.s., An. longipalpis, An. pretoriensis, An. rufipes, Cx. albiventris, Cx. horridus, Cx. macfiei, Cx. perfidious, Cx. pipiens pipiens,Cx. simpsoni and Cx. tigripes)distributed in three genera (Aedes, Anopheles and Culex). Aedes vittatus was by far the most dominant mosquito encountered in all the twenty one (21) sampling locations. Epidemiologically, encountered mosquito species were potential vectors of malaria, yellow fever, dengue,filariasis and the encephalides. Two important malaria vectors (An. gambiae s.s. and An. arabiensis) were genomically identified breeding in sympatry in rock pool habitats within the state. The first hypothesis is therefore rejected.The anthropogenic activities (quarrying) observed on the inselbergs along with weather could be responsible for sustaining theriskof disease vectors andthespreadofvector- bornediseases, thus extension of their geographic distribution in the study area. Diverse invertebrate and vertebrate taxa from protozoans to reptilian as well as microalgae and macrophytes occurred in rock pools within the study locations.Encountered biota were partly potential food organisms while others were potential mosquito predators. The second hypothesis is also rejected.The abundance and distribution of preimaginal stage of mosquitoes in rock pools is determine by the physicochemical condition of the rock pool habitats. Water pH and temperature appeared to play significant determinant roles in the occurrence and abundance of mosquito species in rock habitats, hence third hypothesis is rejected.Knowledge on mosquito ecology in relation to biological and physicochemical parameters facilitating mosquito breeding in rock pools have bearing on vector population and distribution and consequent diseases transmission in the study locations. Therefore, rock pools should be inspected to incriminate vectors and need to be incorporated in mosquito control equations.
Recommendations
There is need to educate residents in the study locations and religious groupson the inselbergs concerning the vectorial roles of the encountered mosquito species in rock pools to prevent the spread of disease in surrounding locations. Introduction of biological competitors and predators of mosquito larvae that are desiccation tolerant into rock pools may also be a more convenient and reduce the need for frequent chemical applications and consistent involvement of residents in antilarval measures on the inselbergs.Therefore, use of mosquito control tools that will not ruin or harm biological control prospect but which incorporate indigenous community participation should be contemplated in rock pools to stem vectorial roles of identified species. Mosquito predatory roles of the potential predators encountered need to be ascertained in order to explore their real biological control potentials against noxious species. Succession pattern of rock pool communities need to be further exposed. Future lines of research should unravel food chain and food web nature of rock pool communities in the study locations and elsewhere. A further study to test the biological and physicochemical variables on mosquito breeding in the laboratory is also recommended.
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