Distribution and Species Diversity of Indoor Biting Mosquitoes (Case Study: Ezza South Local Government Area)

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Distribution and Species Diversity of Indoor Biting Mosquitoes (Case Study: Ezza South Local Government Area)

Mosquitoes are small, midge-like flies that make up the family Culicidae. Females of most species are ectoparasites of mammals, whose tube-like mouthparts (proboscis) pierce the hosts’ skin to consume blood. Thousands of species feed on the blood of various kinds of hosts, mainly vertebrates, including reptiles, amphibians, mammals, birds, and even some kinds of fish. Some mosquitoes also attack invertebrates, mainly arthropods. Though the loss of blood is seldom of any importance to the victim, the saliva of the mosquito often causes an irritating rash that is a serious nuisance.

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The roles of many species of mosquitoes are as vectors of diseases. In passing from host to host, some transmit harmful infections such as malaria, yellow fever, Chikungunya, West Nile virus, dengue fever, filariasis, Zika virus and other arboviruses, rendering it the deadliest animal family in the world (Akram et al., 2009).

They are nuisance species as well as potential transmitters of zoonotic and human diseases such as dengue fever, yellow fever and malaria. Several outbreaks of yellow fever have been reported in southern and central parts of Nigeria (Ezike et al., 2001). Malaria is a deadly disease that causes more than a million human deaths every year, mostly in the tropical areas of Africa, Americas and Asia (WHO, 2010) and remains a major tropical disease of serious public health importance in Nigeria. In Africa, the prevalence of lymphatic filariasis is especially striking, affecting over 40 million people in the sub-Saharan region alone. The abundance, behavior, spatiotemporal distribution and population dynamics of mosquito species is known to be influenced by factors such as climate, seasonality, availability of micro-habitats for breeding, physicochemical parameters of breeding sites and anthropogenic related factors Midega et al., 2010; Kim et al., 2010).

Exploring on mosquito population dynamics present a challenge for Ecologists partly because, seasonal mechanism as influenced by climate can be difficult to predict and understand and thus can generate complex population fluctuation in some insects including mosquitoes (Nunn and Altizer, 2006). The breeding sites preference and physicochemical parameters of mosquito breeding sites of different mosquito species have been extensively studied and are relatively well understood (Muturi et al., 2008). It is a general consensus among several researchers (Akram et al., 2009) that abiotic factors of temperature, relative humidity, altitude and rainfall play a vital role in mosquito development which in turn influences their population density. Environmental changes due to human activities greatly influence the distribution and survival of many mosquito species.

Amusan et al., 2005 opined that the recent increase in agricultural activities and urbanization contributed to the breeding of different mosquito species in southwestern Nigeria. Over population in cities and indiscriminate disposal of wastes materials (including cans and discarded household materials) due to improper town planning and lack of adequate sanitary education increases the potential for breeding disease vector mosquito species. Ezza South with latitude of 7o, 42o 30oN and longitude of 8o 24o 21oE, is a village located in the Ebonyi State of Nigeria characterized with, rapid urbanization, increased population growth, indiscriminate building of residential houses and inadequate amenities to cope with the increasing population represent a good area to investigate. In the light of these growing environmental concerns in the city and the changes in temperatures worldwide, the study was focused on the temporal distribution of some mosquito biting species in various households in Ezza community.

Constant studies on Biology and larval Ecology of mosquitoes have been observed as important tools in mosquito control (Kim et al., 2010) and such studies will help to determine the existing and disappearing mosquito species, relative population densities and the extent of their distribution, seasonal trends and disease infection rates. This study was therefore designed to investigate the mosquito habitats and distribution of existing mosquito in Ezza South LGA of Ebonyi State of Nigeria. This study also discussed the possible public health implications of mosquito’s species abundance on the inhabitants of Ezza South.

The study aimed at assessing the distribution and species diversity of indoor biting mosquitoes species in Ezza South Local Government Area. Other Specific objectives:
i. To identify the morphological futures of indoor biting mosquitoes.
ii. To determine the distribution of mosquitoes species in the study area.
iii. To determine species diversity of indoor biting mosquitoes in-selected house hold in Ezza South.

Insect-transmitted disease remains a major source of illness and death worldwide. Mosquitoes alone transmit diseases to more than 700 million people annually (Taubes 1997). Malaria remains one of the major endemic diseases in the tropics due to high frequency of transmission of Plasmodium species by a large number of Anopheles mosquitos. (Appawu et al., 2001; Awolola et al., 2002).

Mosquito species

Anopheles mosquitoes
The genus Anopheles currently includes 465 formally named species that are disproportionately divided between seven subgenera: Anopheles (cosmopolitan, 182 species), Baimaia (Oriental, one species), Cellia (Old World, 220 species), Kerteszia (Neotropical, 12 species), Lophopodomyia (Neotropical, six species), Nyssorhynchus (Neotropical, 39 species) and Stethomyia (Neotropical, five species). Four of the subgenera, Anopheles, Cellia, Kerteszia and Nyssorhynchus, include the species that transmit human malarial parasites. Most vector species of Anopheles have been found to comprise complexes of sibling species. (Awolola et al., 2002).
Some species of Anopheles also can serve as the vectors for canine heartworm Dirofilaria immitis, the filariasis-causing species Wuchereria bancrofti and Brugia malayi, and viruses such as one that causes O’nyong’nyong fever. An association of brain tumor incidence and malaria suggests that Anopheles might transmit a virus or other agent that could cause a brain tumor. Steven (2010).

Aedes mosquitoes
The Aedes aegypti mosquito is the main vector that transmits the viruses that cause dengue. The viruses are passed on to humans through the bites of an infective female Aedes mosquito, which mainly acquires the virus while feeding on the blood of an infected person.
Within the mosquito, the virus infects the mosquito mid-gut and subsequently spreads to the salivary glands over a period of 8-12 days. After this incubation period, the virus can be transmitted to humans during subsequent probing or feeding. The immature stages are found in water-filled habitats, mostly in artificial containers closely associated with human dwellings and often indoors. WHO (2009).
Flight range studies suggest that most female A. aegypti may spend their lifetime in or around the houses where they emerge as adults and they usually fly an average of 400 metres. This means that people, rather than mosquitoes, rapidly move the virus within and between communities and places. Dengue infection rates are higher outdoors and during daytime, when these mosquitoes (Stegomyia) bite most frequently. However, A. aegypti breed indoors and are capable of biting anyone throughout the day. The indoor habitat is less susceptible to climatic variations and increases the mosquitoes’ longevity. Dengue outbreaks have also been attributed to A. albopictus, A. polynesiensis and several species of the A. scutellaris complex. Each of these species has a particular ecology, behaviour and geographical distribution. A. albopictus is primarily a forest species that has become adapted to rural, suburban and urban human environments (WHO 2009).

Species of this genus are found breeding in freshwater habitats such as pools, ditches, ponds, and even in effluents of sewage treatment plants. Species in this genus are considered to be of medical importance in that they have been proven to be the primary vector of St. Louis Encephalitis and also play an active role in the transmission of West Nile Virus. They are most active at dusk, but are known to be active daytime biters (WHO 2009).

This genus is the primary vector for Eastern Equine Encephalitis. This species does not feed on humans; therefore, it cannot transmit the virus to humans. It feeds actively on birds, cycling the virus from bird to bird. They are most often found in wooded swamps and in crypts left by the roots of fallen trees.
2.1.5 Mansonia
This genus is similar to Coquillittidia, in that it is very aggressive and feeds primarily on larger mammals. It is most active at sunset. Like Coquillittidia, Mansonia larvae are associated with aquatic plants, including water lettuce, water hyacinth, and cattails, using an attenuated siphon to attach to roots to obtain oxygen. Mansonia will often fly great distances in search of blood meals. Adults of this genus are unlikely to be of medical importance (WHO 2009).

Once an individual genus, Aedes has now been divided into 2 different genera. Species of these genera are found in temporary floodwater pools, fresh and brackish marshes, and in natural and artificial containers. Adults are abundant and bite readily outdoors at all hours of the day. It is not uncommon for them to enter homes to feed on humans. Certain species are medically important in the transmission of yellow fever and dengue (WHO 2009).

This genus is considered to be extremely aggressive. Most of the species are known to feed on larger mammals, including humans, and are known to travel long distances in search of blood meals. Species of this genus breed primarily in temporary floodwaters, such as woodland pools, roadside ditches, and pastures. Some of the largest species of mosquitoes in Florida come from this genus. Psorophora are not known to be vectors of any common diseases in Florida. They are primarily active in early evening but are known to bite during the day in shady areas (WHO 2009).

Species of this genus are most commonly found in ground pools, swamps, and grassy edges of lakes. They feed primarily on reptiles and amphibians, and are not known to bite humans. They are readily caught in light traps. Adults of this genus are unlikely to be of medical importance.

This genus is closely associated with bromeliads and pitcher plants. The adults lay their eggs in the bromeliads, where the larvae develop. Adults are not known to travel far from the bromeliad habitats. They are not a common vector, nor are they an aggressive species, unless humans travel into an area that has bromeliads (WHO 2009).

Life cycle of mosquito
Mosquito passes through four different stages that do not resemble themselves during metamorphosis just like all other flies. These stages include: egg, larva, pupa, and adult which can otherwise be called the imago. In most species, adult females lay their eggs in stagnant water; some lay eggs near the water’s edge; others attach their eggs to aquatic plants. Each species selects the situation of the water into which it lays its eggs and does so according to its own ecological adaptations. Some are generalists and are not very fussy. Some breed in lakes, some in temporary puddles. Some breed in marshes, some in salt-marshes. Among those that breed in salt water, some are equally at home in fresh and salt water up to about one-third the concentration of seawater, whereas others must acclimatize themselves to the salinity. Wigglesworth (1933). Such differences are important because certain ecological preferences keep mosquitoes away from most humans, whereas other preferences bring them right into houses at night.

Some species of mosquitoes prefer to breed in phytotelmata (natural reservoirs on plants), such as rainwater accumulated in holes in tree trunks, or in the leaf-axils of bromeliads. Some specialize in the liquid in pitchers of particular species of pitcher plants, their larvae feeding on decaying insects that had drowned there or on the associated bacteria; the genus Wyeomyia provides such examples — the harmless Wyeomyia smithii breeds only in the pitchers of Sarracenia purpurea.
However, some of the species of mosquitoes that are adapted to breeding in phytotelmata are dangerous disease vectors. In nature, they might occupy anything from a hollow tree trunk to a cupped leaf. Such species typically take readily to breeding in artificial water containers. Such casual puddles are important breeding places for some of the most serious disease vectors, such as species of Aedes that transmit dengue and yellow fever. Some with such breeding habits are disproportionately important vectors because they are well-placed to pick up pathogens from humans and pass them on. In contrast, no matter how voracious, mosquitoes that breed and feed mainly in remote wetlands and salt marshes may well remain uninfected, and if they do happen to become infected with a relevant pathogen, might seldom encounter humans to infect, in turn.

Figure1. Life cycle of mosquito

The first three stages of mosquito metamorphosis of which egg, larva, and pupa are largely aquatic. These stages last 5 to 14 days, depending on the species and the ambient temperature, but there are important exceptions. Mosquitoes living in regions where some seasons are freezing or waterless spend part of the year in diapause; they delay their development, typically for months, and carry on with life only when there is enough water or warmth for their needs. For instance, Wyeomyia larvae typically get frozen into solid lumps of ice during winter and only complete their development in spring. The eggs of some species of Aedes remain unharmed in diapause if they dry out, and hatch later when they are covered by water (Spielman et al., 2001).

Eggs hatch to become larvae, which grow until they are able to change into pupae. The adult mosquito emerges from the mature pupa as it floats at the water surface. Bloodsucking mosquitoes, depending on species, sex, and weather conditions, have potential adult lifespans ranging from a week to several months

Mosquito habits of oviposition vary considerably between species, and the morphologies of the eggs vary accordingly. The simplest procedure is that followed by many species of Anopheles; like many other gracile species of aquatic insects, females just fly over the water, bobbing up and down to the water surface and dropping eggs more or less singly. The bobbing behavior occurs

Figure 2. Eggs of mosquito
among some other aquatic insects as well, for example mayflies and dragonflies; it is sometimes called “dapping”. The eggs of Anopheles species are roughly cigar-shaped and have floats down their sides. Females of many common species can lay 100–200 eggs during the course of the adult phase of their lifecycles. Even with high egg and intergenerational mortality, over a period of several weeks, a single successful breeding pair can create a population of thousands.
Many other species, especially members of the genus Mansonia, lay their eggs in arrays. The latter are usually attached to the under-surfaces of waterlily pads. Their close relatives, the genus Coquillettidia, lay their eggs similarly, but not attached to plants. Instead, the eggs form layers called “rafts” that float on the water. This is a common mode of oviposition, and most species of Culex are known for the habit, which also occurs in some other genera, such as Culiseta and Uranotaenia. Anopheles eggs may on occasion cluster together on the water, too, but the clusters do not generally look much like compactly glued rafts of eggs.
In species that lay their eggs in rafts, rafts do not form adventitiously; the female Culex settles carefully on still water with her hind legs crossed, and as she lays the eggs one by one, she twitches to arrange them into a head-down array that sticks together to form the raft. (Spielman et al., 2001).

Aedes females generally drop their eggs singly, much as Anopheles do, but not as a rule into water. Instead, they lay their eggs on damp mud or other surfaces near the water’s edge. Such an oviposition site commonly is the wall of a cavity such as a hollow stump or a container such as a bucket or a discarded vehicle tire. The eggs generally do not hatch until they are flooded, and they may have to withstand considerable desiccation before that happens. They are not resistant to desiccation straight after oviposition, but must develop to a suitable degree first. Once they have achieved that, however, they can enter diapause for several months if they dry out. Clutches of eggs of the majority of mosquito species hatch as soon as possible, and all the eggs in the clutch hatch at much the same time. In contrast, a batch of Aedes eggs in diapause tends to hatch irregularly over an extended period of time. This makes it much more difficult to control such species than those mosquitoes whose larvae can be killed all together as they hatch. Some Anopheles species do also behave in such a manner, though not to the same degree of sophistication. (Huang et al., 2006).

The mosquito larva has a well-developed head with mouth brushes used for feeding, a large thorax with no legs, and a segmented abdomen. Larvae breathe through spiracles located on their eighth abdominal segments, or through a siphon, so must come to the surface frequently. The larvae spend most of their time feeding on algae, bacteria, and other microbes in the surface microlayer.
They dive below the surface only when disturbed. Larvae swim either through propulsion with their mouth brushes, or by jerky movements of their entire bodies, giving them the common name of “wigglers” or “wrigglers”. Larvae develop through four stages, or instars, after which they metamorphose into pupae. At the end of each instar, the larvae molt, shedding their skins to allow for further growth.

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