CHAPTER ONE
1.0 INTRODUCTION
Mosquitoes are slender and relatively small insects, usually measuring about 3– 6 mm in length. Some species, however, can be as small as 2mm while others may be as long as 19 mm (Service, 2008). The long antennae have numerous whorls of hair, short in the female and long and bushy in the male. In most species of mosquitoes, the mouthparts of the female are long, adapted for piercing and for sucking blood. The male, which feeds on nectar and water, has rudimentary mouthparts. Females of this group prefer the blood of warm-blooded animals. When they bite, they inject some of their salivary fluid into the wound, causing swelling and irritation. Many inject infectious micro-organisms and thus transmit such diseases as malaria, yellow fever, dengue, and filariasis (Patel et al, 2012).
There are some 3300 species of mosquitoes belonging to 41 genera, all contained in the family Culicidae (Service, 2008). This family is divided into three subfamilies: Toxorhynchitinae, Anophelinae (anophelines) and Culicinae (culicines). Mosquitoes have a worldwide distribution; they occur throughout the tropical and temperate regions and extend their range northwards into the Arctic Circle. The only areas from which they are absent are Antarctica, and a few islands. They are found at elevations of 5500mand down mines at depths of 1250m below sea level (Service, 2008).
The most important pest and vector species belong to the genera Anopheles,
Culex, Aedes, Ochlerotatus, Psorophora, Haemagogus and
Sabethes.Anophelesspecies, as well as transmitting malaria, are vectors of Filariasis (Wuchereriabancrofti, Brugiamalayi and Brugiatimori) and a few arboviruses. Certain Culexspecies transmit Wuchereriabancrofti and a variety of arboviruses. Aedes species are important vectors of yellow fever, dengue, encephalitis viruses and many other arboviruses, and in a few restricted areas they are also vectors of Wuchereriabancrofti and Brugiamalayi. Species in the very closely related genus Ochlerotatus also transmitfilariasis and encephalitis viruses.
Mansonia species transmit Brugiamalayi and sometimes Wuchereriabancrofti and a few arboviruses. Haemagogus and Sabethes
mosquitoes 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 South America, as well as a few transmitting arboviruses (Service, 2008).
Many species, although not carriers of any disease, can nevertheless be troublesome because of the serious biting nuisances they cause.
The mosquito is one of the insects that have come to be known by man especially in homes for their bites which elicits the formation of antibodies. This is due to the venom that contains toxic protein, which may be inoculated as a result of these bites. It can also cause sharp-pains with some allergic tendencies. Although it does not only bite, but can also serve as nuisance by causing discomfort to their hosts (especially higher vertebrates) as a result of their sounds(Richard, 1993).
Mosquitoes are also widely spread due to their high adaptability, higher reproductive rate, wings, which makes them long distance travellers. Mosquitoes lay their eggs in places where stagnant waters are found. For example pools, ditches, gutters, rivers, streams and other places (Patel et al., 2012)
Although some species of mosquitoes do not bite people, rather they prefer birds or amphibians hosts. Certain mosquito species prefers to feed during the daytime, while others feed at night (Ilahi,2013). Various mosquito species have evolved to seek out and lay their eggs in specific locations (Patriciaet al., 2014).
Female mosquitoes lay their eggs only in water; some species lay their eggs in running water, others in woodland pools, marshes, swamps, estuaries, or in containers such as rain barrels (Service, 2008).
1.1 STATEMENT OF THE RESEARCH PROBLEM
Mosquitoes are vicious biters and their bites constitute biting nuisance, allergic reactions, skin irritations, scratching, restlessness and sleepless nights (Onyidoet al., 2009). Some biteduring the day while others bite during the night or at both night and day periods. Through their blood sucking habits, they act as vectors of a variety of human pathogens including viruses, bacteria, protozoa and helminthic diseases. They transmit to man such deadly diseases as malaria, yellow fever, filariasis,dengue and various forms of viral encephalitis (Ukpaiand Ajoku, 2003).
The anopheles mosquitoes especially, Anophelesgambiae, transmit malaria and filariasis. The Aedesmosquitoes particularly Aedesaegypti, A. albopictus, A. africanus, A. luteocephalusand A. simpsoni, transmit yellow fever, dengue, haemorrhagic fevers and various forms of viral encephalitis. The Culexmosquitoes particularly Culex quinquefasciatus are very important transmitters of filarial worms especially Wuchereriabancrofti which causes elephantiasis. They also transmit various forms of viral encephalitis (Onyidoet al., 2009).
Mosquitoes also bite livestock and transmit some animal diseases like fowl pox disease of poultry, myxomatosis of rabbits, rift valley fever of sheep, encephalitis of horses and heartworm disease of dogs (Service, 1980).
All these diseases cause high death toll on both human and animal populations and lead to poor socio-economic development of many countries.
1.2 SIGNIFICANCE OF THE RESEARCH
The mosquitoes remain a major vector of killer diseases in every part of the world, and Nigeria is not an exception. They also cause nuisance by the sound they make. But they serve as a vital ecological function in that their larvae, pupae, and adults are important food source for fishes, birds, bats, frogs and insects (Patricia et al., 2014).
Although the occurrence of various species of mosquitoes may be seen to vary from one location to another, the result obtained in this study would high-light some important information on the diversity and distribution of mosquitoes as well as help in designing an effective control measure.
1.3 AIM AND OBJECTIVES OF THE RESEARCH
The aim of the research is to determine the relative abundance and
distribution of mosquito species within Sokoto Metropolis.
The objectives of this research are to:
• Identify the species within the areas under study.
• Determine the most abundant species within the area.
• Determine the distribution of mosquito species within the study areas based on area of collection, sex and feeding state.