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INSECTS
Entomology is the study of insects. There are well over 1,000,000 different known species of insects in the world, and some experts estimate that there might be as many as 10,000,000. They are divided up into 32 orders (depending on whose taxonomic system you use) of which the largest is the Beetles (Coleoptera) with 125 different families around 500 000 species. In fact one in every four animals on this planet is a beetle.
INSECTS
INSECT BODY PARTS
The exoskeleton is the hard body covering of insects sometimes referred popularly as the shell of the insect. It protects the internal organs and provides anchorage for the muscles of the insect. The most visible parts of the body of an adult insect are the head, the antennae, the mouthparts, the thorax, the wings, the legs, and the abdomen. Head: The head is the anterior of the three body regions of an adult insect. It bears the eyes (usually a pair of compound eyes), the antennae and the mouthparts. Mouthparts: The mouthparts of adult insects can be of different types. In many species they are of the chewing type, for example in grasshoppers and beetles. Others have sucking mouthparts for example shaped like stylets in bugs and aphids or shaped like a coiled tongue in butterflies and moths. The different types of mouthparts determine how the insect feeds. Antennae: The head of most adult insects bears a pair of antennae. Insects use the antennae to detect odors or they use them as tactile (touch) organs. Antennae are very variable in form and size. Thorax: The thorax is the middle of the three body regions of an adult insect. It is composed of 3 segments. It bears 3 pairs of legs (one on each segment) and usually 2 pairs of wings. Some insects have only 1 pair of wings. Legs: Adult insects have 6 legs. Each of the segments of the thorax bears 1 pair of legs. The legs are segmented. Often the last segment of the leg bears a small claw. In some insects, the legs are specially adapted for jumping. Wings: Most adult insects have 2 pairs of wings, but some (for example flies) have only 1 pair of wings. Usually the wings are membranous but in some insects they can be leathery or hard. Sometimes the wings bear hairs or small scales.
Abdomen: The abdomen is the posterior of the three body regions of an adult insect. It is composed of 11 segments. The abdomen bears the external genitalia of the insect. In female insects these consist of an ovipositor. METAMORPHOSIS Metamorphosis is the series of developmental changes an insect passes in its growth from the egg to the adult. Metamorphosis requires a change in form, habit food and size. Growth requires molting. During molting the insect sheds its external skeleton. During the short period its skin remains soft and the new skeleton is formed, the insect grows rapidly. Simple metamorphosis In simple metamorphosis the wings develop externally during the larval stages. The larval stages, which are called nymphs, look very similar to the adult insect. There is no pupal stage. Egg nymph 1 nymph 2 nymph 3 etc. adult Other names used for the immature stage or nymph are larva, naiad and instar. The nymph stage may be divided into several instars. The nymph resembles the adult form and there is no change in food requirements. At each step of growth, the exoskeleton is molted. Complete metamorphosis In a complete metamorphosis the wings develop internally during the larval stages. The larval stages look quite different from the adult. Between the last larval stage and the adult stage there is a pupal stage which usually is inactive. Egg larva pupa adult MOSQUITO LIFE CYCLE All mosquitoes have one common requirement-- they need water to complete their life cycle. Some mosquitoes lay individual eggs on the sides of tree holes or discarded containers, or in depressions in the ground that will hold water. The eggs can lay dormant for several years. Some eggs will hatch when they are flooded by rainfall. Several flooding and drying cycles are usually required for all of the eggs to hatch that are laid by a particular female mosquito. Other mosquitoes lay eggs directly on the surface of water. The eggs are attached to one another to form a raft or the individual eggs float on the water. These eggs hatch in 24-48 hours releasing larvae that are commonly called "wrigglers" because you can often see the larvae wriggling up and down from the surface of the water. Generally, the larvae feed on microorganisms and
- Proper identification of the mosquito species.
- Obtaining information about the biology and behavior of these particular species.
- Locating and eliminating breeding sites, particularly artificial sites that may be as close as your own backyard.
- Using appropriate chemical controls measures, including personal protection. Most mosquito species survive the ,inter, or overwinter, in the egg stage, awaiting the spring thaw, when waters warm and the eggs hatch. A few important species spend the winter as adult, mated females, resting in protected, cool locations, such as cellars, sewers, crawl spaces, and well pits. With warm spring days, these females seek a blood meal and begin the cycle again. Only a few species can overwinter as larvae. Mosquito-borne diseases, such as malaria and yellow fever, have plagued civilization for thousands of years. Organized mosquito control in the United States has greatly reduced the incidence of these diseases. However, there are still a few diseases that mosquitoes in New, Jersey can transmit, including Eastern Equine Encephalitis and St. Louis Encephalitis. The frequency and extent of these diseases depend on a complex series of factors.
ARBOVIRUSES
Arthropod-borne viruses (termed "arboviruses") are viruses that are maintained in nature through biological transmission between susceptible vertebrate hosts by blood-feeding arthropods (mosquitoes, sand flies, ceratopogonids "no-see-ums", and ticks). Vertebrates can become infected when an infected arthropod bites them to take a blood meal. The term 'arbovirus' has no taxonomic significance. Arboviral encephalitis can be prevented in two major ways: personal protective measures to reduce contact with mosquitoes and public health measures to reduce the population of infected mosquitoes in the environment.
COMMON DISEASES
SAINT LOUIS ENCEPHALITIS
Encephalitis- An inflammation of brain tissue producing an acute febrile illness, almost always viral in origin. It may range from mild to life threatening. Depending on the extent and area of inflammation symptoms can include fever, delirium, and confusion progressing to unconsciousness, cranial nerve palsies, paresis, paralysis, involuntary movement and abnormal reflexes. Intracranial pressure (ICP ) may become elevated Often an encephalitis will involve the meninges as well. The first recognized cases of Saint Louis Encephalitis (SLE) occurred in 1933 in the city of St. Louis. Hence the origin of the name, Saint Louis Encephalitis. SLE is a virally induced disease. Since 1933 several outbreaks of SLE infection have occurred in North America and some Caribbean islands. In recent years epidemics of up to 2000 cases have occurred in both urban and suburban areas in the Ohio Mississippi river basin, eastern and central Texas and Florida.
The virus is transmitted to man and other hosts by short-lived mosquitoes of the genus Culex. These mosquitoes are very common in the USA. Humans (and most other mammals) are very poor carriers of SLE. Birds also carry the virus. When a Culex mosquito bites a bird carrying this virus, the virus is transmitted to the mosquito. Likewise, if a mosquito carrying the virus bites a bird, the virus is transmitted to the bird. In this manner the virus circulates between birds and mosquitoes. But, the virus adversely affects neither the bird nor mosquito. If an infected mosquito bites a human, then the virus is transmitted to the human. In the United States SLE is the most common of all mosquito borne cases of encephalitis. Whenever conditions favor the proliferation of Culex, there is an increased risk that an outbreak of SLE will occur. In the United States these conditions include above average summer temperatures, and a period of deficient rainfall followed by heavy rains. These conditions are most favorable for producing stagnant pools of water, which are ideal for Culex to breed in. Epidemics tend to occur sporadically and most often take place between July and September. Both the very young and the old have the greatest risk of becoming seriously ill if bitten by an infected mosquito.. The overall mortality rate for SLE is 9%, but it approaches 30% in those over age 65. EASTERN EQUINE ENCEPHALITIS Eastern Equine Encephalitis (EEE) is a mosquito-borne viral disease. As the name suggests, EEE occurs in the eastern half of the US. Because of the high case fatality rate, it is regarded as one of the more serious mosquito-borne diseases in the United States. TRANSMISSION: What is the EEE transmission cycle? How do people become infected with EEE virus? EEE virus is transmitted to humans through the bite of an infected mosquito. The main EEE transmission cycle is between birds and mosquitoes. Several species of mosquitoes can become infected with EEE virus. The most important mosquito in maintaining the enzootic (animal-based, in this case bird-mosquito-bird) transmission cycle is Culiseta melanura. Horses can become infected with, and die from, EEE virus infection. ETIOLOGIC AGENT: What causes EEE? Eastern equine encephalitis virus is a member of the family Togaviridae, genus Alphavirus. Closely related to Western and Venezuelan equine encephalitis viruses HUMAN CLINICAL FEATURES: What type of illness can occur? Symptoms range from mild flu-like illness to encephalitis (inflammation of the brain), coma and death. The EEE case fatality rate (the % of persons who develop the disease who will die) is 35%, making it one of the most pathogenic mosquito-borne diseases in the US. It is estimated that 35% of people who survive EEE will have mild to severe neurologic deficits INCIDENCE: How many and where have human disease cases occurred?
The 2002 WNV epidemic was the largest recognized arboviral meningoencephalitis epidemic in the Western Hemisphere and the largest WN meningoencephalitis (inflammation of the spinal cord and brain) epidemic ever recorded. Significant human disease activity was recorded in Canada for the first time, and WNV activity was also documented in the Caribbean basin and Mexico. In 2002, 4 novel routes of WNV transmission to humans were documented for the first time:
- blood transfusion,
- organ transplantation,
- transplacental transfer ,
- breast-feeding. As November 25, 2003, Tennessee: 25 reported cases; 1 death. The State with the highest incident of WN virus is Colorado, with 2477 reported cases and 45 deaths, followed by Nebraska (1727 cases; 21 deaths) and South Dakota (1001 cases; 13 deaths.) These numbers reflect both mild and severe human disease cases that have been reported to ArboNet by state and local health departments during 2003. ArboNet is the national, electronic surveillance system established by CDC to assist states in tracking West Nile virus and other mosquito-borne viruses. Of the 8567 cases reported as of the above date, 5686 cases (66%) were reported as West Nile Fever (milder disease), 2505 (29%) were reported as West Nile meningitis or encephalitis (severe disease) and 376(4%) were clinically unspecified. http://www.cdc.gov/ncidod/dvbid/westnile/surv&control.htm TRANSMISSION CYCLE West Nile (WN) virus is amplified during periods of adult mosquito blood-feeding by continuous transmission between mosquito vectors and bird reservoir hosts. Infectious mosquitoes carry virus particles in their salivary glands and infect susceptible bird species during blood-meal feeding. Competent bird reservoirs will sustain an infectious viremia ( virus circulating in the bloodstream ) for 1 to 4 days after exposure, after which these hosts develop life-long immunity. A sufficient number of vectors must feed on an infectious host to ensure that some survive long enough to feed again on a susceptible reservoir host. People, horses, and most other mammals are not known to develop infectious-level viremias very often, and thus are probably "dead-end" or incidental-hosts. In the United States, infected mosquitoes, primarily members of the Culex species, transmit West Nile virus. HUMANS
West Nile Fever is a mild disease in people , characterized by flu-like symptoms. West Nile fever typically lasts only a few days and does not appear to cause any long-term health effects. More severe disease due to a person being infected with West Nile virus can be West Nile encephalitis, West Nile meningitis or West Nile meningoencephalitis. Encephalitis refers to an inflammation of the brain, meningitis is an inflammation of the membrane around the brain and the spinal cord. Meningoencephalitis refers to inflammation of the brain and the membrane surrounding it. BIRDS West Nile virus has been detected in dead birds of at least 138 species. Although birds, particularly crows and jays, infected with WN virus can die or become ill, most infected birds do survive. There is no evidence that a person can get WN virus from handling live or dead infected birds. Persons should avoid bare-handed contact when handling any dead animals, and use gloves or double plastic bags to place the bird carcass in a garbage bag or contact their local health department for guidance. DOGS AND CATS West Nile virus does not appear to cause extensive illness in dogs or cats. There is a single published report of WN virus isolated from a dog in southern Africa (Botswana) in 1982. West Nile virus was isolated from a single dead cat in 1999. A sero-survey in New York City of dogs in the 1999 epidemic area indicated that dogs are frequently infected. Nonetheless, disease from WN virus infection in dogs has yet to be documented. There is no documented evidence of person-to-person or animal-to-person transmission of WN virus. HORSES Available data suggest that most horses infected with West Nile virus recover, results of investigations indicate that West Nile virus has caused deaths in horses in the United States. http://www.cdc.gov/ncidod/dvbid/westnile/birds&mammals.htm http://www.cdc.gov/ncidod/dvbid/westnile/q&a.htm
