Exploring The Life Of The Mosquito Biology Essay

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Mosquitoes are widely known throughout the world and mosquito using several water bodies for breeding (WHO, 1982). Larval species can be found in almost every type of non-flowing aquatic habitat from the marshy edges of large lakes, provided that fish or tadpoles are not present through swamps and marshes of all types and sizes along sections of rivers, streams, or ditches where the water is not flowing to small collections of water in rock crevices, tree or stump holes, leaves of pitcher-plants and artificial containers (Wood, Dang and Ellis, 1979). The climatic and environmental factors are influenced directly and indirectly to the distribution of mosquitoes (Mafiana et al., 1998).

Mosquitoes prefer an environment with certain resources which are food, shelter, favourable temperature, rainfall, breeding site and suitable humidity in sufficient amount and at the appropriate time for survival and development for the eggs of female mosquito to hatch (Romoser & Stoffolano, 1998). The breeding of various mosquito species is recently increase contributed of the recent increase in ecological and environmental modification due to agricultural activities and urbanization (Amusan et al., 2005).

Temperature and the availability of appropriate aquatic breeding habitats are the two environmental variables that most impact the abundance of mosquitoes. Temperature impacts both the survivorship and developmental rate of mosquitoes; surface wetness, as mentioned above, limits the population size of sub-adult mosquitoes. These two parameters, temperature and surface wetness, will be used to force the model mosquito population (Kettle, 1995). Constant studies on biology and larval ecology of mosquitoes have been observed as important tools in mosquito control. Such studies will help to determine the existing and disappearing mosquito species and the extent of their distribution (Mafiana et al., 1998 & Anyanwu et al., 1999). Mosquito can cause more human suffering than any other organisms. Mosquito bite cause severe skin irritation through an allergic reaction to the mosquito's saliva which can cause human skin red bump and itching. Mosquito also carry disease that afflict human such as malaria, yellow fever, encephalitis and dengue virus which a mosquito bites infected the host, the virus will be transferred into it, and the transmission chain starts again (WHO, 1997).

The life cycle of the mosquito is begins with the female mosquito will lay eggs at any surface water, which hatches as a larvae in the right conditions. The larvae then develop into several instar stages before entering pupation. After the pupation, the mosquito emerges as an adult which is also called as amigo. Adults generally mate within the first few hours of emergence, and then the adults will rests on the surface water for a short time to allow itself to dry and all its body parts to harden. Blood feeding does not occur for a couple of days after the adults emerge including the mating. Once fully developed, the female mosquito will proceed to find a protein source for their eggs which is blood. After biting, the female rests while take care of their eggs and repeat thegonotrophic cycle again.

1.2 Objectives

The objectives of this study are :

To know the relationship between mosquito breeding and environment.

To know the effects of environmental factors on mosquito abundance.

To study the life cycle of mosquito.

To study the effect of mosquito to human health.

1.3 Significances of study

Environment plays an important role on life cycle of mosquito. So, in this study and research, it can show us the interactions between environment and life cycle of mosquito. In this research study, I would like to know the effects of environmental factors such as pH, rainfall and temperature of the site on mosquito abundance by using the larvae one. Mosquito abundance is actually relate with the amount of rainfall and contribute to increase the number of larval breeding sites, the spatial relationship between larval habitat availability and adult mosquito abundance is not clear.

In these study also, I would know the disease that mosquito can bring which effect the human health. We can know that mosquitoes are a vector agent that carries disease causing viruses and parasites from person to person without catching the disease themselves. Furthermore, I will know the methods used for mosquito control that can reduce the disease that mosquito can bring to human. Depending on the situation, source reduction, biocontrol, insecticides to kill larvae and to be specific, the adults may be used to manage mosquito populations.

In these research study also, we would like to know when the suitable breeding time for mosquito is actually. It is said that many species disappear almost completely during the dry season and it will be most productive towards the end or just after the wet season, when most species will have built up to a peak and the limits of the breeding sites have temporarily stabilized.

1.4 Problem Statement

Mosquito had been known for a century which is they carry diseases which can cause human to death. These can be described as the mosquito can cause more human suffering than any other organism. Furthermore, mosquito bite can cause severe skin irritation through an allergic reaction to the mosquito's saliva which can cause human's skin itching and red bump. Mosquito carry several diseases which are malaria, filarial diseases (dog heart worm), virus dengue, encephalitis and yellow fever. These diseases can suffer human being and can cause human being to death.

Nowadays, mosquito distribution is increasing in Malaysia because of certain conditions that contribute to mosquito breeding. More than that, population in Malaysia also increases by year to year. So, this also will increase the number of cases that inflict the human by mosquito.



2.1 Environment

In general, environment is actually referred to the surrounding of something or an object. The natural environment is contrast with the built environment which includes the areas and components that are strongly influenced by the human. An ecosystem is a kind of natural which include all of plants, animals and microorganisms in an area functioning together with all of the non-living physical factors of the environment.

There have been several studies that have focused on how environmental factors affect the mosquitoes breed (Yee 2008). The environmental factors and climatic are influenced the distribution of mosquitoes which in directly or not (Mafiana et al., 1998). Mosquitoes prefer an environment with certain condition that help their breeding which in appropriate amount and time for survival and development (Romoser & Stoffolano, 1998).

The efficacy of any mosquito larvae may however, depend upon its bioavailability for target larvae in the environmental water together with the own tolerance level of each larval. Several environmental parameters may influence the performances of a given larvae (Bourguet et al., 1996).

2.2 Biodiversity

According to Convention on Biological Diversity (CBD) stated that 'biodiversity' means that the variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part which includes diversity within species between species and of ecosystems.

In the last decade, biodiversity concerns have been in the forefront of conservation efforts worldwide (Environment Canada, 1994 and UNEP 1995). Biodiversity has been defined in various ways (McNeely et al., and Salwasser, 1990) but the term has generally been used in a very comprehensive manner meaning the variability of life which are composition, structure and function.

Biodiversity can be represented as an interlocked hierarchy of elements on several levels of biological organization (Noss, 1992). Since the term 'biodiversity' transcends all levels of life from genes to communities and all spatial and temporal scales (Noss, 1990 and Savard, 1994), it has generated a lot of confusion and misunderstanding (West, 1993 and Lautenschlager, 1997). However, when understood and used properly, biodiversity concepts can provide a useful framework for conservation efforts (Savard, 1994).

According to Mittermeier et al., (1999) and Myers et al., (2000) biological rich areas are found in a high range across the altitudinal variation associated with diverse habitats. Further, as per their views, most of the hot spots and areas of high biological diversity are concentrated in hilly and mountainous ranges where there are diverse habitats. There are evidenced which the rich mosquito fauna diversity, but there is almost no record about species richness and its composition in diverse habitats (Mahesh and Jauhari, 2000).

2.3 Mosquito

Mosquitoes are insects belonging to the order Diptera, the True Flies. Like all True Flies, they have two wings, but unlike other flies, mosquito wings have scales. Female mosquitoes' mouthparts form a long piercing-sucking proboscis. Males differ from females by having feathery antennae and mouthparts not suitable for piercing skin. A mosquito's principal food is nectar or similar sugar source. There are over 2500 different species of mosquitoes throughout the world; about 200 species occur in the United States with 77 species occurring in Florida (Darsie et al., 2002).

2.3.1 Life Cycle of Mosquito

The mosquito is actually been through four separate and distinct stages of its life cycle which are egg, larva, pupa and adult. Eggs are laid one at a time or attached together to form "rafts". They float on the surface of the water. Most eggs hatch into larvae within 48 hours, others might withstand subzero winters before hatching. Water is a necessary part of their habitat.

The larva lives in the water and comes to the surface to breathe. Larvae shed their skins four times, growing larger after each shed. The larvae feed on microorganisms and organic matter in the water. During the fourth molt the larva changes into a pupa.

The pupa stage is a resting time which is non-feeding stage of development but pupa are mobile, responding to the light changes and moving with a flip of their tails towards the bottom or protective areas. This is the time the mosquito changes into an adult. When development is complete, the pupa skin splits and the adult mosquito (imago) emerges.

The newly emerged adult rests on the surface of the water for a short time to allow itself to dry and all its body parts to harden. The wings have to spread out and dry properly before it can fly. Blood feeding and mating does not occur for a couple of days after the adults emerge.

2.3.2 The Vector

Mosquitoes are known vectors of several disease causing pathogens which affect many millions of people all over the world. Aedes aegypti is known to carry dengue, yellow fever and chikungunya while malaria is carried by Anopheles stephensi and filarial disease by Culex quinquefasciatus (WHO, 1992). Mosquito transmitted diseases continue to be a moajor source of illness and death. Most parasitic diseases are tropical and ontensifying globalization and climatic change are increasing the risk of contracting arthropod borne illnesses (Guenier et al., 2004).

Repellents play an important role in protecting humans from the bites of insect pests. An effective and safe repellent will be useful in reducing human and vector contact and thereby help in the reduction of vector borne disease transmission (Kalyanasundaran & Mathew, 2006). Meanwhile, according to Gupta & Rutledge (1994), the use of personal protection measures such as the application of repellents of exposed skin has long been advocated to minimize human contact with vector and nuisance mosquitoes.

Chemical repellents are important in protecting people from blood feeding insects, ticks, mites and other arthropods and may therefore also reduce transmission of arthropod borne diseases (Brown & Hebert, 1997). People living in the remote rural areas and the poorer section of society endlessly suffer from many vector borne diseases, particularly malaria, due to lack of simple and cheap methods of personal protection (Karunamoorthi et al., 2008).

2.3.3 Transmission

Virus transmission of mosquito will affect the human after being bitten and human is the reservoir of the virus. In mosquito, the virus will take for about 8 to 10 days to develop. A female mosquito may transmit the virus to its progeny through transovarian transmission, but it is not frequent. These virus or disease from mosquito will transmit into human circulation during the blood meal time. The virus will develop in the human circulation which the human incubation period takes about 3 to 14 days. If a mosquito bites, the virus will then transmit into the host and the transmission chain starts again (WHO, 1997). Vertical transmission of dengue virus is very rare. Nonetheless, 2 cases were reported in Malaysia in 1996 (Chye et al., 1997).

2.3.4 Factor Contribute to the Disease Outbreak

The occurrence of mosquito disease is depends of several factors, including the density of mosquito vectors. For example the dengue virus which is carried by the Aedes aegypti that is needed to sustain dengue virus transmission epidemically or endemically has yet to be determined. Virus transmission increased by denser human population. Urbanization in tropical countries has resulted in both a proliferation of Aedes aegypti and an increase in the number of susceptible human hosts (WHO, 1997).

According to McMichael and Woodruff (2008), mosquito borne infections tend to increase with warming and certain changes in rainfall pattern. Higher rainfall will heighten the disease transmission. Therefore, climate change will affect the potential, seasonal transmission and geographic range of various vector borne diseases. These diseases would include all water borne diseases, such as malaria, dengue fever and yellow fever (Haines et al., 2006).

Climate change will affect the biodiversity and the ecosystem goods and services that we rely to human health. Changes in temperature and rainfall effect the distribution of the diseases vectors, such as Aedes mosquitoes (Haines et al., 2006). Recent reviews suggest that dengue's range and incidence may be changing as a result of climate change (Gubler, 2002).

Most of the transmissions of mosquito borne diseases are sensitive to weather conditions for several reasons here, mosquito need standing water to breed, and a warmer temperature is critical to adult feeding behavior, the rate of larval development and speed of replicate of virus (Hales and Panhius, 2001).

Haines et al., (2006) stated that changes in climate that can affect the transmission of vector borne infectious disease include temperature, rainfall changes, humidity, soil moisture and sea level rise and it will cause the variation of the overall incidence of the disease, where less, the geographical distribution of disease also change.

2.3.5 Breeding and Larval Habitat

According to Queensland Government (2005), the mosquito is frequents backyards in search of containers holding water inside or outside the home. For example cans, buckets, jars, pot plants dishes, vases, birdbaths, boats, discarded with no rims tyres, roof gutters blocked by leaves, containers, tarpaulins and black plastic. It also can breed in natural containers like fallen palm fronds. Besides that, even in a drier condition it also breeds in water in subterranean sites such as wells, telecommunication pits, sump pits and gully traps.

Furthermore, according to Queensland Government (2005) also stated that climate of tropical and subtropical regions are very suitable for mosquito breeding. This is because of high temperature and high appearance of quiescent water body. With this, it makes the climate in Malaysia is tropical and the temperature are within 20°C to 30°C throughout the year and with high average rainfall which is almost 2500mm in the Peninsular Malaysia and it is become the most suitable breeding conditions and habitat for mosquito.

According to White (2004), mosquitoes breed in water, occasionally depositing eggs directly on water, but generally using a variety of moist surfaces, tree holes, and containers and the development time for larvae depends on specific environmental conditions such as temperature, nutrient supply, degree of available light, with most tropical mosquito larvae developing in approximately 1 week, while the larvae of many species endemic to temperate zones may overwinter.

Human activities, such as the production of a large amount of environmental debris that holds water pools including disposable bottles, cans, discarded tires and storage of water on or around living premises when reliable piped home water supplies are unavailable or unreliable, may markedly increase available mosquito breeding sites and have been particularly implicated, as mentioned above, in the marked dissemination of Ae. aegypti (along with the dengue cases it very efficiently vectors) throughout most of the tropical world including areas from which both had been eradicated (Gubler, 1989).

2.3.6 Dengue Diseases

Dengue diseases are included dengue fever (DF), dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS) are serious mosquito-borne diseases. These diseases are commonly found in Southeast Asian countries including Malaysia (Lee, 2000).

The geographical spread of both the mosquito vectors and the viruses has led to the global resurgence of epidemic dengue fever and emergence of dengue hemorrhagic fever (dengue/DHF) in the past 25 years with the development of hyper endemicity in many urban centers of the tropics (WHO, 2009).

According to World Health Organization (WHO, 2009) reports, an estimated 50 - 100 million dengue infections occur worldwide every year, including up to 500,000 cases of DHF. Forty per cent of the world's population resides in areas where transmission occurs.

Dengue fever patient have symptoms of aches in the muscles and joints, headaches and fever which last for two or three days. The phase of the illness is replaced by a period of one to three days duration when there is a return to both normal body temperature and good health. But the fever soon returns, together with pains and rash which covers most of the body apart from the face. Although dengue is course by debility it is rarely fatal (Snow, 1974).

2.3.7 Control of Mosquito Diseases

Nowadays, mosquito diseases have been well known around the worldwide. They carry diseases which can cause human to death and suffer for their life. For examples malaria, filarial diseases, viruses dengue, encephalitis and yellow fever. These diseases have cause millions of infections occur worldwide every year. So, we should prevent or control the mosquito diseases from spreading around the world.

An effective way to prevent all of these diseases is to control the growth of mosquito population. A recent alternative way that originated from advances in genetic research is the possibility to produce transgenic mosquitoes. Although this alternative is already a success for the case of malaria mosquitoes. Now, it has been suggested and there are some research initiatives in this direction, which genetically modified mosquitoes introduced in the environment, can exterminate malaria once and for all (Catteruccia et al., 2003).

The second alternative way for mosquito control is by adulticide spraying, it is far more controversial, and its effectiveness is limited. Some of health department officials and Mosquito Abatement Districts (MAD) employees pointed out that studies have shown only a 30% reduction in mosquito population after spraying. Studies like these are controversial because as community of the environment, this experiment is actually doing in a controlled environment that exaggerates spraying effectiveness, so percentages in the field are less. Nevertheless, evidence suggests that combined use of both larvicides and adulticides to reduce numbers of mosquitoes will decrease the number of West Nile Virus (WNV) infections in humans (Bowman et al., 2005).

Many districts have reduced their use of adulticide spraying because of concerns about health and environmental impacts. However, adulticide spraying may be justified during a disease outbreak (Peterson et al., 2006).

There are approach to decrease or minimize the incidence of these diseases to spread and to control mosquito vectors mainly by application of insecticides to larval habitats, destroying unwanted containers and educating the public (Corbel, 2004). During epidemics, these measures are complemented by insecticide space-spraying against adult mosquitoes. However, aerial toxicants for eradicating A. aegypti are not effective, since this species is highly domesticated and many adults rest in hidden places indoors (Ciccia, 2000). Attacking the breeding site of mosquito with larvicides is a potential and effective way to diminish mosquito population for a higher percent than other ways.

2.4 Factor Effect Mosquito Breeding

Mosquitoes prefer an environment with certain resources which are food, shelter, favourable temperature, rainfall, breeding site and suitable humidity in sufficient amount and at the appropriate time for survival and development for the eggs of female mosquito to hatch (Romoser & Stoffolano, 1998). The breeding of various mosquito species is recently increase contributed of the recent increase in ecological and environmental modification due to agricultural activities and urbanization (Amusan et al., 2005).

Wu et al. (2007) indicated that the weather variability such as monthly maximum, minimum temperature, rainfall and relative humidity identified as a meaningful and significant indicators for the increasing occurrence of dengue fever in Taiwan region. It is also widely accepted that the distribution and dynamics of vector borne diseases infections are particularly sensitive to meteorological conditions, by virtue of the sensitivity of many species of mosquitoes to variations in temperature, relative humidity, rainfall, evaporation and quantities of standing water quality used as breeding sites (Johansson et al., 2009). Specifically, the epidemic behavior of dengue viruses seemingly relates closely with fluctuations in temperature and rainfall (Halstead, 2008).

2.4.1 Rainfall

Precipitation is one of the most important elements for the breeding and development of mosquitoes (Kelly-Hope et al., 2004). All mosquitoes have aquatic larval and pupa stages and therefore require water for breeding (Clements, 1992). Considerable evidence has occurred to show that heavy rainfall and flooding can lead to increased mosquito breeding and outbreak of diseases. For example, high rainfall has been associated with outbreaks since 1928, and 46 to 50 outbreak location received higher than average rainfall in the preceding month (Kelly-Hope et al., 2004).

The association of dengue epidemics with rainfall could be explained by increases in adult survival and feeding activity of the vector mosquito. However, some researches gave contradicting evidence on the relationship of meteorological factors to dengue incidence (Kanchanapairoj et al., 2000).

According to Mafiana et al., (1998), tree holes can only retain water for a short time period and dry up at the time there is no rain. This is the reason to explain the low contribution of tree holes to the breeding of mosquitoes.

2.4.2 Temperature

Warmer temperature can increase or reduce survival rate, depending on the vector, its behavior, ecology and many other factors. A 2°C increase in temperature would simultaneously lengthen the lifespan of the mosquito and shorten the extrinsic incubation period of dengue virus, resulting in more infected mosquitoes for a longer period of time (Focks and Barrera, 2007).

Temperature and the availability of appropriate breeding habitats are the two environmental variables that most impact the abundance of mosquitoes (Kettle, 1995). Temperature is actually can cause both the survivorship and development rate of mosquitoes.