Mosquitoes -Characteristics, Life Cycle and Control Measures — howMed

Mosquitoes -Characteristics, Life Cycle and Control Measures

Habits of mosquitoes

A knowledge of the habit is essential from the point of view of controlling of arthropods as will as for a proper understanding of the point they play in disease transmission.

Throughout the world (Tropical & temperate region).

Only female mosquitoes can bite in the evening or in the early part of the night (Haematophagous).

Anopheles prefer clean water for breeding while culex breed in dirty water. Aedes breed in artificial collection of water.

Feeding :

Anthrophilic (Those insects which prefer to suck the blood from human beings)

Zoophilic (Those insects which prefer to suck the blood from animals)

Resting:

Endophilic (those insects which rest inside the house)

Exophilic (those insects which rest outside the house in bushes)

The normal range of flight is about 2-3 kms from their breeding places.

It depends upon the environmental conditions, average life period of female mosquitoes are 2-3 weeks and male are short lived.

Medical importance

Genus Anopheles: Malaria

Genus Culex: Filarial& viral encephalitis

Aedes: Yellow fever & dengue fever

Difference between Anopheles/Aedes Mosquitoes

Life cycle of mosquito

Metamorphosis is complete.

1. Egg: Anopheles female lays eggs singly in fresh water, size of eggs is about 1mm, boat shaped, lateral float are present. About 100-250 eggs are laid. Eggs are not visible by naked eye.

Culex female lays eggs in stagnant & polluted water in raft, they are oval in shape and lateral float are absent.

2. Larva: After 2-3 days larva emerge from egg, actively swimming on water surface and feed on algae, fungi & bacteria. Larva is about 1-6 mm long. Body is divided into three parts (head, thorax & abdomen). Spiracles (respiratory organs) are present on abdomen. Palmate hairs are present on abdomen which help larvae to float in water.

3. Pupa: after 5-7 days larva becomes pupa. Pupa is comma shaped and moves actively on water surface. The body is divided in cephalothorax and abdomen. Two small respiratory trumpets are present on thorax. It does not feed. The pupal stage lasts for 1-2 days.

4. Adults: when the adult emerges from pupa, it rest for a while on the pupal skin then flies away. Under favorable environmental conditions the life cycle is completed in 7-10 days. Normally the adult mosquito lives for about 2-3 weeks.

Control Measures

1. Biological control: Use of parasites, predator (fish & frog) and pathogens. The best known fish are Gambusia affinis and lobister reteculatus.

2. Genetic control: Release of sterile male mosquitoes in the field. Which will compete with the natural fertile male mosquito in mating & the population will be automatically reduced.

3. Environmental control: To eliminate their breeding places. This is also known is source reduction. Filling, leveling and drainage of breeding places.

4. Chemical control:

  • Anti larval chemicals like Paris green, mineral oil.
  • Anti adult chemicals like Melathian, Fenthian and abate.

5. Protection against mosquito bite

  • Screening of doors, windows and ventilation’s of house/hospital.
  • Mosquito net should be tucked around the bed.
  • Insects repellants like deet , dimethyle, phthlate and dimethyle carbate are available in local market in shape of oil, creams & lotions. They should be used on the exposed parts of the body.

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Different Types of Mosquitoes

Mosquitoes exist across the world, with the exception of Antarctica. More than 3,000 mosquito species have been identified in both the Arctic and subtropics. They are categorized into 39 different genera.

About 174 species can be found in North America and Mexico. Different types of mosquitoes have different feeding and breeding habits. The four most common types of mosquitoes in the United States are the house mosquito, the southern house mosquito, the Asian tiger mosquito and the yellow fever mosquito.

House mosquito (Culex)

Some of the most common types of mosquitoes in the United States are called house mosquitoes. Species of mosquitoes that belong to this group include Culex Pipiens and Culex restuans Theobald.

Cx. Pipiens is most common to the Northern part of the United States. Pale brown in color with white stripes, it is often found in polluted water that has been left standing. Storm drains, birdbaths, pet dishes and old tires are popular breeding sites for these types of mosquitoes. The female mosquito of this species can lay anywhere from 50 to 400 eggs at one time. These eggs typically take 10 to 14 days to hatch although they can take longer, depending on the weather. Culex restuans is a very similar species in looks and habits, but is more prevalent in the Eastern and Central parts of the United States.

Both of these mosquito types can transmit a variety of different viruses and parasites to humans.

Southern mosquito (Culex quinquefasciatus)

This species of mosquitoes, also sometimes referred to as Culex fatigans, is most common in tropic and sub-tropic regions. It shares many of the same physical and behavioral aspects of the house mosquito, but is found in Southern areas of the United States and is present throughout Florida. Also a nighttime feeder, this mosquito is the primary vector of the St. Louis encephalitis virus and can also transmit West Nile virus (WNV).

Asian tiger mosquito (Aedes albopictus)

This species of mosquitoes can be identified by the bright white or silver stripes on its abdomen, thorax and legs. Unlike other types of mosquitoes belonging to Culex, the female Asian tiger mosquito is a daytime feeder and can be an aggressive biter. Males do not bite.

Types of mosquitoes belonging to the genus Aedes have similar breeding habits. Females often lay eggs in clean, standing water. They are drawn to containers such as birdbaths or flowerpots. Eggs that have been flooded after a rainstorm can hatch in a short amount of time under the correct temperatures, making it easier for these mosquito types to spread. Species of mosquitoes belonging to Aedes tend to be weak flyers and often won’t travel more than one-half of a mile away from their original breeding sites.

The Asian tiger mosquito was first discovered in the United States in 1985. Since then, it has competed for space with the yellow fever mosquito, which was once the most prominent species of Aedes in the country. The Asian tiger is a vector of more than 30 viruses, but only a few are known to affect humans, according to University of Florida Entomology and Nematology Department. These diseases include equine encephalitis, Cache Valley virus, dengue, and St. Louis and LaCrosse encephalitis viruses. Despite this, different types of mosquitoes belonging to Aedes have proven more efficient than the Asian tiger at transmitting disease.

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Yellow fever mosquito (Aedes aegypti)

The yellow fever mosquito has been known to the United States for many centuries. It caused more U.S. troop casualties during the Spanish-American war than the war itself, as a result of transmitting the yellow fever.

Because both types of mosquitoes belong to the Aedes genus, this species of mosquitoes have similar feeding and breeding habits to the Asian tiger. However, the population of the yellow fever mosquito has declined in many areas following the arrival of the Asian tiger mosquito, although it is still prevalent in some regions.

The yellow fever mosquito is more commonly found in urban areas of Southern Florida, and in cities along the coasts of Texas and Louisiana. It can also be found in Southern parts of the United States and up the East Coast to New York.

The nuisance of mosquitoes can keep you and your family from enjoying the outdoors. And controlling these insects can be challenging and is not something that you should try to DIY. Contact us today to learn about our mosquito service.

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Mixed Economy: Definition, Types, Features and Problems

Let us make an in-depth study of Mixed Economy:- 1. Definition of Mixed Economy 2. Types of Mixed Economies 3. Features of Mixed Economy 4. Problems of Mixed Economy 5. Measures for the Efficient Working of a Mixed Economy.

Definition of Mixed Economy:

Meaning and Definition:

1. Mixed Economy is a two Wheel economy in which Private Sector and Public Sector run together.

In other words—it is neither pure capitalism nor pure socialism but it is the mixture of the two.

In this economy private enterprise is not permitted to function freely and uncontrolled. The Government intervenes to control and regulate private enterprise.

2. Hanson has written that—”Mixed Economy is a golden mean by socialism and capitalism”.

3. Joseph E. Stigtitz has defined the concept in a much more simple manner. He says that Mixed Economy is a “Mixture of Public and Private Decision-making.”

4. Prof. A. Samuelson has defined—”Mixed Economy as on which primarily relies on price mechanism for economic organisation but uses a variety of government interventions, such as taxes, spending and regulation to handle macro-economic instability and market failures.”

Further, a mixed economy implies the operation of both Private Sector and Public Sector. The enterprises in the private sector are not permitted to work freely through price mechanism and are often controlled by the state in order to stimulate them to work within the frame work of the national economic planning.

On the other-hand the state in the underdeveloped countries like India actively participates in economic activities, so as to minimise the evils of pure capitalism and to realise the benefits of the socialism as well.

The evolution of the concept of “Mixed Economy” is the development of the 20th Century. It emerged as a measure to avoid the evils of economic liberty or “Laissez Faire” on the one hand and to realise simultaneously the good qualities of socialisation of means of production on the other.

Types of Mixed Economies:

There are two types of mixed economies:

In one type the ownership of the means of production i.e., farms and factories is owned and controlled by the private sector and the Government merely controls and regulates the functioning of the private sector.

In the second type the government directly participates in productive enterprise side by side with private enterprise. The government sets up industries of its own and invests its own capital and purchases or hires the productive resources and takes the risk of profit or loss like an ordinary entrepreneur.

There are also Joint Sector which is shared both by Private and the Public Sector.

The U.S.A. and the U.K. are prominent examples of first type of mixed economy while India represents the second type of mixed economy.

Features of Mixed Economy:

The following are the main features of the mixed economy:

1. Co-existence of Public and Private Enterprises:

The main feature of a mixed economy is the co-existence of both Public and Private enterprises. They work together. The industries in Private Sector are managed and operated completely by the Private entrepreneurs. The private entrepreneurs are fully free to develop their industries and to start new industries in this sector.

On the other-hand there is Public Sector in which the enterprises are owned and managed by the State. Usually the basic industries like defence, equipment’s, atomic energy, telecommunication, heavy engineering etc. are allocated in the public sector where as the consumer goods industries, small and cottage industries, agriculture etc. are often given to the Private Sector.

Besides this, the State also ensures to the Private Sector not to inter-venue in its functioning and provides several incentives and facilities for the development and the smooth functioning of the sector, so as to make the country’s economy rather more economically strong and powerful.

2. State Control over Private Sector:

In such an economy the State imposes certain necessary measures to regulate and control the enterprises relating to the private sector, so that they make undertake their work in accordance with the national objectives and not only in their own interests.

The Licensing System is an effective instrument in the hands of the State by which it controls and regulates the direction of private industrial investment and production. The other measures of control over private sector which it generally uses are appropriate monetary and fiscal policies. As such the State gives them rebates and tax concessions and credit facilities at the reasonable rates, so as to encourage the private entrepreneurs to invest their savings in the required and right direction.

3. Price Mechanism and State Directions:

Other important characteristics of a mixed economy may be its operation – both by the price mechanism and the state directives. In the public concern all economic decisions relating to production, prices, marketing and investments are taken by the state authorities. On the other-hand it is price mechanism which decides all the important economic policy matters in private sector. The private entrepreneurs take the important economic decisions on the basis of the price and cost analysis of the market and with an object of realising maximum profits.

4. Consumer’s Sovereignty is Protected:

In a mixed economy the sovereignty of the consumers is almost protected which is not possible in a socialist economy. The consumers can purchase commodities freely from the market of their own choice which are produced by the private entrepreneurs according to the consumer’s demand or preferences.

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The state sometimes imposes price control over the goods produced by the private entrepreneurs so as to protect the consumers against the ruthless exploitation undertaken by the capitalists or producers of the private sector.

Besides this, the state also introduces public distribution mechanism followed by the rationing of essential goods in short supply, so that the limited available goods may be fairly supplied and distributed among the people in the society.

5. Proper Protection is provided to Weaker Sections of the Society Specially Workers and Labourers:

In the initial stage of Industrial Revolution, the producers or capitalists, ruthlessly exploited the working class. The state thus realised its responsibility to protect this class from exploitation by the industrialists and producers.

It is with this view that the state has implemented a number of Labour Acts to regulate and control the working conditions of labour, such laws are Minimum Wages Act; Industrial Dispute Act; The Workman’s Compensation Act; The Maternity Benefit Act; The Employees State Insurance Act; The Employees Provident Fund Act etc.; provide protection to the workers in respect of employment, injury or casualty by accident, disease, maternity and old age benefits. The state also takes essential steps if there is any dispute arisen in the industry in the interest of the workers.

6. State Takes Measures to Control Monopoly and Concentration of Economic Powers in the Hands of Few:

In a mixed economy a monopolist uses his powers against the interest and welfare of the consumers and wants to realise maximum profits out of his total production which is possible either by reducing the total output or by raising the prices of the commodity.

It results in the growing inequalities in the society and enlarging exploitation of the workers. In 1969 MRTP Act was passed to control or restrict monopolist and the concentration of economic power in the Indian economy.

7. It Reduces Economic Disparities:

A Mixed Economy is often blamed for stimulating economic disparities in the country. But the states in such economies take necessary steps to reduce inequalities of income and wealth. The growing inequalities of income usually may create disparities of opportunities of education and jobs and may further generate class-strug­gle between the rich and poor workers.

Ultimately, the entire society may be divided into two major camps the rich and the poor or the ‘haves’ and the ‘have not’s”. It is with this view that a welfare state always tries to reduce economic disparities through the proper fiscal and credit policies.

With the elements or characteristics written above we can come to this conclusion that in a mixed economy both sectors-Public and Private work together. On the one hand there are Public and Private work together on the other-hand there are Public enterprises completely owned and managed by the state and the private concerns fully organised and managed by the individual owners on the other.

However, both the sectors still new a few restrictions to remove or minimise all other economic distortions and disparities existing in the economy; so as to develop those sectors according to the main stream of the economic developments.

Problems of Mixed Economy:

Sometimes it has been experienced that the economy does not work well successfully under a mixed economy. In Indian economy, there is a Public Sector to a large extent on the one hand and a weak and controlled Private Sector on the other. As a matter of fact, the Public Sector flourishes in a planned economy. The undue importance to the first at the cost of the latter tends to some sort of problems in the pace of economic development.

The difficulties may follow as under:

1. The Private Sector has to work under certain restrictions and control and it is likely to carry out its programmes under a National Plan. But it is experienced in Indian Economy that the process of private sector ultimately depends on the profit motive system and it is generally against the objectives of national planning.

2. The transportation of Private Sector into Public Sector, as a State Policy of nationalization of private enterprises, tends to a lot of fear and confusions against private entrepreneurs.

3. The Public Sector is encouraged throughout the planning period but its performance is not satisfactory and is almost misfit in the framework of national planning. With the result that none of them fulfills the objectives of national planning and hence it is one of the major factor causing the failure of a long-term planning in India.

Measures for the Efficient Working of a Mixed Economy:

Following are the important steps which can be taken up for the efficient working of a Mixed Economy:

1. Political Stability at the Centre:

There should be a strong central government along with the political stability.

2. Timely Execution of Plans is Essential:

The prompt and timely execution of plans in inevitably necessary.

3. State Policy should be Clear:

The state policy of nationalisation should be clear and understandable to general public.

4. Private Sector should Work within the National Guidelines:

The Private Sector should work strictly within the structure of National Economic Planning.

5. To Maintain balance between Public and Private Sector:

The Government of India has made it clear that in future, the Government has no programme of nationalisation of any industry and therefore has decided to maintain a balance between the two sectors. So no danger of take-over by the Government.

www.economicsdiscussion.net

Types of mosquitoes — description and features of existence

modified from: Kettle, D.S. (1995). Medical and Veterinary Entomology. CAB International. Wallingford

  • Natural History
  • Mosquito borne diseases
  • Clinical Presentation
  • Laboratory Diagnosis
  • Treatment and Control
  • Confirmation and Enquiries
  • Links

Mosquitoes are blood sucking insects that are responsible for the transmission of many diseases throughout the human and animal populations of the world. Within Australia there are more than 300 different species of mosquito but only a small number are of major concern. Several important human diseases are transmitted throughout Australia by these insects including Dengue fever, Australian encephalitis, Ross River virus disease and Barmah Forerst virus disease; malaria has been transmitted locally in Australia only rarely in recent decades. In addition to being disease vectors, mosquitoes can cause major disruptions, through their persistent biting, to occupational, recreational and social activities.

Mosquitoes belong to the family of flies called Culicidae and are small fragile insects

modified from: Goddard, J. (1993). A Physician’s Guide to Arthropods of Medical Importance. CRC Press. Florida.

that have six delicate legs and two wings covered in scales. The head of a mosquito is equipped with a projecting proboscis which conceals and protects the long piercing and sucking mouthparts. These biting insects have a complex life cycle; the immature stage is totally aquatic and the adult is terrestrial. The adult female returns to a water habitat for a brief period to lay each batch of eggs. Mosquito species vary in their breeding habits, biting behaviour, host preferences and flight range. Most mosquitoes disperse less than two kilometres; some move only a few metres away from their original breeding place, others can fly some 5 or 10 kilometres, and a few species will disperse up to 50 kilometres downwind from the larval habitats.

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On average, a female mosquito will live 2-3 weeks, but the male’s lifespan is shorter. Within their lifetime both adult male and female will feed on nectar and plant fluids, but it is only the female that will seek a blood meal. The majority of species require this blood meal as a protein source for egg development. Female mosquitoes are attracted to a potential host through a combination of different stimuli that emanate from the host. The stimuli can include carbon dioxide, body odours, air movement or heat. Upon locating a suitable host, the female will probe the skin for a blood capillary then inject a small amount of saliva containing chemicals which prevent the host’s blood from clotting. This is often the pathway for potential pathogens such as viruses to enter a host. After engorging on the host’s blood the female will find a resting place to digest her meal and develop eggs before flyingoff to deposit them in a suitable aquatic habitat.

On hatching, the young larvae (wrigglers) feed continuously and grow through four different instars or moults. Larval development is dependent on the availability of food and prevailing conditions, particularly temperature, but generally takes at least one to two weeks. The final larval instar develops into an active comma-shaped pupa (tumbler) from which the adult mosquito emerges about 2 days later to feed, mate and develop eggs for the next generation.


Mosquito-borne diseases in Australia

Diseases transmitted by mosquitoes in Australia include Dengue fever, Australian encephalitis, Ross River (RR) virus disease and Barmah Forerst (BF) virus disease. Dengue is the most important viral disease transmitted by mosquitoes afflicting humans in a world context. Clinical symptoms range from mild fevers, to a severe and potentially life threatening haemorrhagic disease. In Australia, Dengue fever is restricted to Quensland where the major vector Aedes aegypti occurs. «Australian encephalitis» (AE), or «Murray Valley encephalitis» are synonyms for a clinical syndrome caused by infection with Murray Valley encephalitis virus or Kunjin virus. Symptoms are variable, from mild to severe with permanent impaired neurological functions, to sometimes fatal. Cases of AE occur sporadically in northern Australia and especially in the northwest of WA, but there have been no cases of MVE recorded in southeastern Australia since 1974. Ross River and Barmah Forest disease have been collectively known as «Epidemic Polyarthritis», however the two diseases have a slightly different clinical picture. A wide variety of symptoms may occur from rashes with fevers, to arthritis that can last from months to years with RR virus infection. RR disease is the most commonly reported mosquito transmitted disease to humans (over 6,500 cases in 1997) and occurs in all states of Australia. There are occassional local epidemics with hundreds to thousands of infections, with many going unreported. BF disease occurs in most states of Australia, although the annual number of cases are around 1/10th that of RR disease. A series of outbreaks during the early 1990’s has highlighted the increasing importance of BF disease. Malaria in Australia has been endemic, but was declared eradicated from the country in 1981. However, approximately 700-800 cases are imported annually from travellers infected elsewhere.


Clinical Presentation

Sensitivity to mosquito bites varies with individuals, most people have only a mild reaction but others can have severe symptoms from the saliva of mosquitoes. Typical symptoms include swelling, redness and irritation at the puncture site. If the bites are scratched or traumatized, they may become infected with bacteria and a secondary infection can be initiated, especially on the lower limbs. The diagnosis of mosquito-borne diseases including Dengue, Australian encephalitis, and Ross River and Barmah Forest viruses can only be confirmed with appropriate blood tests.


Laboratory Diagnosis

Mosquitoes are identified with the aid of a stereo microscope and taxonomic keys. The detection of viruses and other pathogens in mosquitoes is undertaken. Detection of viruses or virus antibodies in human blood is a procedure performed in the arboviral serology unit at Westmead Hospital.


Treatment and Control

There are many methods of control that can be implemented to reduce the number of mosquitoes. Local councils may use larvicides (pesticides that kill the larvae) which prevent mosquitoes from maturing to adults. In areas where there is a disease outbreak fogging may be considered as an option in order to kill the infected adult mosquito population. Other methods could include the use of parasites, predators or pathogens of mosquitoes to assist in reducing the population, but there is no biological control agent other than fish currently available for use against mosquitoes.

Simple measures can be taken by individuals to limit their contact with mosquitoes, Areas that are known to be infested with large numbers of mosquitoes shold be avoided. Activities that are scheduled for outdoors, especially around dusk should be limited, as the biting activity of many mosquitoes will peak during this period. Clothing that has long sleeves and long pants should be worn when visiting areas that are infested with mosquitoes. A chemical repellent should be used on exposed areas of skin, but not repeatedly on young children. See «Beathing the Bite of Mosquito-borne Disease, A Guide To Personal Protection Strategies Against Australian Mosquitoes» for detailed information on the appropriate use of repellents.

Windows and doors should be screened; water tanks also, using a small gauge mesh to exclude mosquitoes from these potential breeding sites. Empty all containers throughout the garden that hold water such as pot plant saucers, tyres, roof guttering and tins to prevent breeding. Bed nets are an effective barrier against biting insects at home or camping, and can now treated safely with an insecticide. Insecticidal sprays, and coils and electric mats, for use around the house can help in keeping mosquitoes at bay.


Confirmation and Enquiries

Identification of mosquitoes and all other medically important arthropods is preformed through the Medical Entomology Department at ICPMR, Westmead Hospital.

Related Links

(University of South Australia mosquito research group).

(Comprehensive list of mosquito related sites from the United States).

(A review of mosquito seeking behaviour).

(Mosquito Genomics server).

(American mosquito control association).

(Links to mosquito sites in America).

Produced by Merilyn J. Geary, Richard C. Russell, Stephen L. Doggett

medent.usyd.edu.au

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