ABSTRACT
Entomological surveys were conducted to determine the biological and physicochemical parameters influencing mosquito breeding in rock pools on inselbergs in Kaduna State. Available rock pools were searched on the inselbergs fortnightly between June and October, 2013 in 21 settlements distributed in 7 Local Government Areas.This covered theState vegetation from the Guinea Savanna to SudanSavanna.A total of 368 rock pools were sampled for mosquito larvaeusing soup ladle dipper (0.105L) from 269 (69.7%) rock pools harbouring mosquito larvae. Biological (microinvertebrates, macroinvertebrates, macrophytes, algae and vertebrates) and physicochemical (depth, surface area, distances to adjoining pools, temperature, pH, total dissolve solid, electrical conductivity, total suspended solid, turbidity, hardness, dissolve oxygen, biochemical oxygen demand, chemical oxygen demand, phosphate, nitrate and alkalinity) parameters of the pools were determined. Polymerase Chain Reaction was used for the identification of mosquito species of Anopheles gambiaes.s. Of the 31,726 mosquito larvae collected, thirteen species in three mosquito genera(Aedes, Anopheles and Culex) including Ae. vittatus (95.71%),An. arabiensis (0.01%), An. gambiae s.s. (0.1%), An. longipalpis (0.0%), An. pretoriensis (0.0%), An. rufipes (0.02%), Cx. albiventris (0.84%), Cx. horridus (0.33%)Cx. macfiei (0.76%), Cx. perfidiosus (1.65%), Cx. pipiens pipiens (0.44%), Cx. simpsoni (0.0%) and Cx. tigripes (0.0%) bred in rock pools. Aedes vittatuswas the most dominant mosquito encountered in all the 21 sampling locations. PCR–based assay revealed 41.6% amplification of the An. gambiaecomplex sample with 38.9% populations belonging to An.gambiae s.s. whilst the remaining 2.6% were An. arabiensis. Up to 58.4% of the An. gambiae complex could not be identified through PCR even after three runs. ANOVA showed that the abundance of mosquito larvaediffered significantlywith pH of the rock pools (p < 0.05). Highly significant difference existed between the abundance of mosquito larvae and total dissolve solid, electrical conductivity and alkalinity of the rock pools (p < 0.001). The abundance of mosquito larvae did not differ significantly with depth, surface area, total suspended solid, hardness and turbidity of the rock pools (p > 0.05).Principal Component Analysis showed that temperature, electrical conductivity and total dissolve solids were paramount for mosquito breeding in rock pool habitats. Low positive correlation (r = 0.394) existed between dissolve oxygen and abundance of mosquito larvae (p < 0.001). Strong positive correlation (r = 1.000) exist between biochemical oxygen demand and the abundance of mosquito larvae (p < 0.005). Nitrate ( r = 0.047) and chemical oxygen demand had low positive correlation (r = 0.029) with mos quito abundance. Strong positive correlation (r) existed between macroinvertebrate and mosquito abundance(p < 0.001) while microinvertebrates correlated negatively (r) with the abundance of mosquito larvae (p < 0.05) in rock pools.Chlorophytes had widespread occurrence while Microcystis spp. had the highest percentage positivity, being the only cyanophyte associated with mosquito larvae (p < 0.05) in rock pools. Chlorophytum laxumwas predominant amongst other aquatic macrophytes found with mosquito larvae in rock pools. Epidemiologically, the mosquito species encountered are potential vectors of human and animal diseases, hence rock pools should be inspected to incriminate vectors and be incorporated in mosquito control strategies.
CHAPTER ONE
1.0 INTRODUCTION
Mosquitoes are probably the most notoriously undesirable arthropods with respect to their ability to transmit pathogens that cause human disesases such as malaria, dengue, yellow fever, filariasis, viral encephalitides and other deadly diseases. In several parts of the world, the indirect effect of malaria and other mosquito-borne diseases accounted for more deaths as well as reduced production following work losses (Rueda, 2008). Emergence of new vector-borne disease entities and the resurgence of old ones are caused by several factors, which are ecological changes that increase vector densities, such as climate, immunity status of humans, human and potential vector population densities and the presence of suitable reservoir amongst others (Adebote et al., 2006). The increase in economic activities, tourism and human migration have led to more cases of the movement of both disease vectors and the pathogens they carry thereby increasing the biodiversity of mosquitoes around the world (Manguin and Boete, 2010). Diversity of mosquito breeding environment stems from innate preferences shown by d ifferent taxa to the locations and conditions of various aquatic habitats (Adebote et al.,2 008). Oviposition preferences of adult females and the ability of immature stages of mosquitoes to adapt to both biotic and abiotic environmental conditions of a given aquatic habitat determine the abundance and distribution of immature mosquitoes (Dejenie et al., 2002). Mosquitoes have diverse habits that allow them to colonize different kinds of environments. The immature stages of mosquito are thus found in a variety of aquatic habitats including ponds, streams, ditches, swamps, marshes, temporary and permanent pools, rock holes, tree holes, crab holes, lake margins, plant containers (leaves, fruits, husks, tree holes, bamboo internodes), artificial containers (tyres, tin cans, flower vases, bird feeders), and other habitats (Rueda, 2008). They can
thrive in a variety of water conditions such as freshwater, brackish water and or any water quality (clear, turbid or polluted), except in marine habitats with high-salt concentration. Part of the problems militating against effective and sustained control of mosquitoes and the diseases transmitted by them is the overt advantages available to mosquitoes to breed in diverse aquatic media that are naturally occurring and or the creation of human activities.
Rock pools are small bodies of water that undergo recurrent, variable wet-dry phases, making them temporary intermittent pools (Levas, 2006). The relatively small nature of rock pools and the few macroscopic biota constituents make it easier to determine their community structure. Rocky outcrops have a profound influence on the distribution and abundance of biodiversity worldwide (Lindenmayer et al., 2008). Such environments a re well documented as biological hotspots which often support unique biotic communities and high levels of endemism. The composition of mosquito fauna of a po
ol is influenced by its temporary or permanent nature. The highly variable rock pool environment, with continuously changing abiotic and biotic conditions, therefore continuously tests the tolerance limits of the inhabitants (Jocque et al., 2010). The physicochemical compositions of water bodies are complicated and determine their condition and fauna composition. They include salts, dissolved inorganic and organic matter, degree of eutrophication, turbidity and presence of suspended mud. Other hydrologic factors that affect preimaginal mosquito populations in water are the presence or absence of plants, temperature, light and shade, hydrogen ion concentration, presence of food substances (living or dead), presence of predacious mosquito larvae, fishes, other insects, crustaceans and arachnids (Okogun et al., 2005). Huggettand Griffiths(1986)attempted to relate the communities occurring in rock pools with the extremes of salinity, hydrogen ion concentration, light and temperature
occurring within them. They concluded that temperature was the most important of these parameters. Daniel and Boyden (1975) investigated diurnal variations in water pH, carbon dioxide, salinity, as well as temperature and oxygen concentration within intertidal rock pools and concluded that temperature and oxygen concentrationsshowed the greatest variation that were particularly important in controlling community structure.
The biological and physicochemical attributes of aquatic environments may alter adult mosquito vector competence (Kengluecha et al., 2005). Although aquatic habitats of mosquitoes encompass a broad and complex spectrum, the rock pools comprise a distinct group with unique ecological properties (Vezzani, 2007). Rock pools form a distinct class distinguishable into true rock pools and rock edged pools (Okogun et al., 2005). Pool structure is determined by a complex set of biological and physical factors that interact to develop a patchy habitat (Wallenstein et al., 2010). Interactions between climate and geology (e.g. limestone, sandstone, granite) generally determine the morphology and hydrology of rock pool habitats, with hydro periods ranging from several days up to the whole year. Pool volume is usually small, resulting in strongly fluctuating environmental conditions, low conductivity and wide variations in pH (from 4.0 to 11.0) and temperature (from freezing point to 40°C) often with well-marked diel cycles(Wallenstein et al., 2010). Rock pools usually form in shallow depressions in the rock (Ranta, 1982). Rock pools in general are oligotrophic systems open to nutrient inp uts and outputs (Jocque et al., 2010). Even a brief rain shower may, depending on the t opography, fill a rock pool to overflowing. They are mosaically distributed habitats characterized by unpredictable changes in their water contents (Ranta, 1982). Enrichment happens mainly through bacterial degradation of dead aquatic organisms, faeces from large (terrestrial) vertebrates and organic material blown in. Immediately
after filling, dissolved nitrogen and phosphorus concentrations may be quite high, but decline quickly because of nutrient uptake by organisms and a reduced rate of nutrient supply from the sediment (Jocque et al., 2010).
The algal composition in rock pools exhibit a marked gradient in many places, with green algae dominating pools that occur higher on the shore, whereas brown and red algae are dominant at lower shore levels, where common species from the adjacent sub-tidal communities occur (Wallenstein et al., 2010). In rock pools, Metaxas and Scheibli ng (1993) showed that competitive hierarchies involving 3 species of Daphnia can lead to competitive exclusion. Rock pools harbour freshwater communities and are located higher on the shore between the rocky intertidal and terrestrial habitat. Because of the comparatively small spatial dispersal capacity of mosquito larvae, larval control is the principal and most effective tool for mosquito-borne disease management (Siobhan et al., 2009). To critically audit the environment for the sources of mosquito that may be involved in disease transmission include searches of aquatic habitats in rock pools amongst several other breeding sites and determination of factors that support habitation (Adebote et al., 2008).
The biological and physicochemical factors affecting the breeding of mosquitoes in rock pool habitats have been the subject of rather little ecological interest and research. This could be attributed to the relative inaccessibility of these productive mosquito habitat types that should be given priority in mosquito abatement programmes. Few attempts have also been made to describe the distribution patterns of rock pool biotas in relation to any suspected influence of physicochemical conditions to which the pools are subject and how these in turn affect species composition and relative abundance of preimaginal mosquitoes. Typically in areas where mosquito breed in rock pools, not
every pool is often colonized by juvenile stages to the extent that several apposed pools could be devoid of mosquito while few other neighbouring pools have high density of larvae. Such disjointed larval colonization has not been fully investigated to unravel its ecologic undertone and potential applicability in control.
1.1 Statement of Research Problem
The biological and physicochemical factors that influence the behaviour of mosquitoes to colonize and breed in rock pool habitats in Kaduna State have not been fully investigated and therefore largely unknown.
1.2 Justification
This studywas designed to unravel key ecological factors that modulate the breeding of mosquito vectors of human and animal diseases in rock pool habitats in Kaduna State, Northern Nigeria, where such habitats are known to be abundant but relatively inaccessible to routine control operations. The knowledge of inherent pool characteristics that make rock pools to be desirable or otherwise for mosquito breeding will enhance knowledge of the biology of the insects and the ability to control them.
1.3 Aim of the Study
To evaluate the biological and physicochemical contents of rock pool breeding habitats of mosquitoes in Kaduna State, Northern Nigeria.
1.4 Objectives
i. To determine the species composition and relative abundance of mosquito breeding in rock poolhabitats in Kaduna State.
ii. To determine the biota composition of rock pools link with breeding of mosquitoes.
iii. To determine the physicochemical parameters of rock pools.
i. Mosquitoes do not colonize and breed in rock pool habitats.
ii. The colonization and breeding of mosquitoes in rock pools are not influenced by biological factors.
iii. The colonization and breeding of mosquitoes in rock pools are not influenced by physicochemical factors.
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