Effects on biota

Animals
Pesticides inflict extremely widespread damage to biota, and many countries have acted to discourage pesticide usage through their Biodiversity Action Plans.[citation needed]
Animals may be poisoned by pesticide residues that remain on food after spraying, for example when wild animals enter sprayed fields or nearby areas shortly after spraying.
Widespread application of pesticides can eliminate food sources that certain types of animals need, causing the animals to relocate, change their diet, or starve. Poisoning from pesticides can travel up the food chain; for example, birds can be harmed when they eat insects and worms that have consumed pesticides.Some pesticides can bioaccumulate, or build up to toxic levels in the bodies of organisms that consume them over time, a phenomenon that impacts species high on the food chain especially hard.
The USDA and USFWS estimate that about 20% of the endangered and threatened species in the US are , by use of pesticides.

Effects on biota

Plants
Nitrogen fixation, which is required for the growth of higher plants, is hindered by pesticides in soil.The insecticides DDT, methyl parathion, and especially pentachlorophenol have been shown to interfere with legume-rhizobium chemical signaling.Reduction of this symbiotic chemical signaling results in reduced nitrogen fixation and thus reduced crop yields.Root nodule formation in these plants saves the world economy $10 billion in synthetic nitrogen fertilizer every year.
Pesticides can kill bees and are strongly implicated in pollinator decline, the loss of species that pollinate plants, including through the mechanism of Colony Collapse Disorder,in which worker bees from a beehive or Western honey bee colony abruptly disappear. Application of pesticides to crops that are in bloom can kill honeybees,which act as pollinators. The USDA and USFWS estimate that US farmers lose at least $200 million a year from reduced crop pollination because pesticides applied to fields eliminate about a fifth of honeybee colonies in the US and harm an additional 15%.

Soil effectance by pesticides

Many of the chemicals used in pesticides are persistent soil contaminants, whose impact may endure for decades and adversely affect soil conservative.
The use of pesticides decreases the general biodiversity in the soil. Not using the chemicals results in higher soil quality,[verification needed]with the additional effect that more organic matter in the soil allows for higher water retention.This helps increase yields for farms in drought years, when organic farms have had yields 20-40% higher than their conventional counterparts.A smaller content of organic matter in the soil increases the amount of pesticide that will leave the area of application, because organic matter binds to and helps break down pesticides.

Soil effection by pesticides

Many of the chemicals used in pesticides are persistent soil contaminants, whose impact may endure for decades and adversely affect soil conservation.
The use of pesticides decreases the general biodiversity in the soil. Not using the chemicals results in higher soil quality,[verification needed]with the additional effect that more organic matter in the soil allows for higher water retention. This helps increase yields for farms in drought years, when organic farms have had yields 20-40% higher than their conventional counterparts. A smaller content of organic matter in the soil increases the amount of pesticide that will leave the area of application, because organic matter binds to and helps break down pesticides.

Water pesticides

In the United States, pesticides were found to pollute every stream and over 90% of wells sampled in a study by the US Geological Survey.Pesticide residues have also been found in rain and groundwater.Studies by the UK government showed that pesticide concentrations exceeded those allowable for drinking water in some samples of river water and groundwater.
Pesticide impacts on aquatic systems are often studied using a hydrology transport model to study movement and fate of chemicals in rivers and streams. As early as the 1970s quantitative analysis of pesticide runoff was conducted in order to predict amounts of pesticide that would reach surface waters.
There are four major routes through which pesticides reach the water: it may drift outside of the intended area when it is sprayed, it may percolate, or leach, through the soil, it may be carried to the water as runoff, or it may be spilled, for example accidentally or through neglect.They may also be carried to water by eroding soil.Factors that affect a pesticide's ability to contaminate water include its water solubility, the distance from an application site to a body of water, weather, soil type, presence of a growing crop, and the method used to apply the chemical.
Maximum limits of allowable concentrations for individual pesticides in public bodies of water are set by the Environmental Protection Agency in the US. Similarly, the government of the United Kingdom sets Environmental Quality Standards (EQS), or maximum allowable concentrations of some pesticides in bodies of water above which toxicity may occur.The European Union also regulates maximum concentrations of pesticides in water.

Air

Pesticides:


Pesticides can contribute to air pollution . Pesticide drift occurs when pesticides suspended in the air as particles are carried by wind to other areas, potentially contaminating them.Pesticides that are applied to crops can volatilize and may be blown by winds into nearby areas, potentially posing a threat to wildlife.Also, droplets of sprayed pesticides or particles from pesticides applied as dusts may travel on the wind to other areas,or pesticides may adhere to particles that blow in the wind, such as dust particles.Ground spraying produces less pesticide drift than aerial spraying does.Farmers can employ a buffer zone around their crop, consisting of empty land or non-crop plants such as evergreen trees to serve as windbreaks and absorb the pesticides, preventing drift into other areas.Such windbreaks are legally required in the Netherlands.
Pesticides that are sprayed onto fields and used to fumigate soil can give off chemicals called volatile organic compounds, which can react with other chemicals and form a pollutant called ozone, accounting for an estimated 6% of the total ozone production.

Use of pesticides

Contents

1 Air
2 Water
3 Soil
4 Effects on biota
4.1 Plants
4.2 Animals
4.2.1 Birds
4.2.2 Aquatic life
4.2.3 Amphibians
4.2.4 Humans
5 Persistent organic pollutants
6 Pest resistance
7 Pest rebound and secondary pest outbreaks
8 Eliminating Pesticides

Use of pesticides can have unintended effects on the environment.
Over 98% of sprayed insecticides and 95% of herbicides reach a destination other than their target species, including nontarget species, air, water, bottom sediments, and food.Pesticide contaminates land and water when it escapes from production sites and storage tanks, when it runs off from fields, when it is discarded, when it is sprayed aerially, and when it is sprayed into water to kill algae.The amount of pesticide that migrates from the intended application area is influenced by the particular chemical's properties: its propensity for binding to soil, its vapor pressure, its water solubility, and its resistance to being broken down over time.Factors in the soil, such as its texture, its ability to retain water, and the amount of organic matter contained in it, also affect the amount of pesticide that will leave the area.Some pesticides contribute to global warming and the depletion of the ozone layer.

Environmental effects of pesticides

Main article: Environmental effects of pesticides
Pesticide use raises a number of environmental concerns. Over 98% of sprayed insecticides and 95% of herbicides reach a destination other than their target species, including non-target species, air, water and soil.Pesticide drift occurs when pesticides suspended in the air as particles are carried by wind to other areas, potentially contaminating them. Pesticides are one of the causes of water pollution, and some pesticides are persistent organic pollutants and contribute to soil contamination.
In addition, pesticide use reduces biodiversity, reduces nitrogen fixation, contributes to pollinator decline,destroys habitat (especially for birds),and threatens endangered species.
It also happens that some of the pest adapt to the pesticide and don’t die. What is called pesticide resistance, to eliminate the offspring of this pest, will be needed an new pesticide or an increase the dose of pesticide. This will generates more pollution ambient.

Regulation

Preparing for pesticide application.

In most countries, pesticides must be approved for sale and use by a government agency.For example, in the United States, the Environmental Protection Agency (EPA) does so. Complex and costly studies must be conducted to indicate whether the material is safe to use and effective against the intended pest. During the registration process, a label is created. The label contains directions for proper use of the material. Based on acute toxicity, pesticides are assigned to a Toxicity Class.
Some pesticides are considered too hazardous for sale to the general public and are designated restricted use pesticides. Only certified applicators, who have passed an exam, may purchase or supervise the application of restricted use pesticides.[23] Records of sales and use are required to be maintained and may be audited by government agencies charged with the enforcement of pesticide regulations.
In Europe, recent EU legislation has been approved banning the use of highly toxic pesticides including those that are carcinogenic, mutagenic or toxic to reproduction, those that are endocrine-disrupting, and those that are persistent, bioaccumulative and toxic (PBT) or very persistent and very bioaccumulative (vPvB). Measures were approved to improve the general safety of pesticides across all EU member states.
Though pesticide regulations differ from country to country, pesticides and products on which they were used are traded across international borders. To deal with inconsistencies in regulations among countries, delegates to a conference of the United Nations Food and Agriculture Organization adopted an International Code of Conduct on the Distribution and Use of Pesticides in 1985 to create voluntary standards of pesticide regulation for different countries.The Code was updated in 1998 and 2002.The FAO claims that the code has raised awareness about pesticide hazards and decreased the number of countries without restrictions on pesticide use.
Three other efforts to improve regulation of international pesticide trade are the United Nations London Guidelines for the Exchange of Information on Chemicals in International Trade and the United Nations Codex Alimentarius Commission[citation needed]. The former seeks to implement procedures for ensuring that prior informed consent exists between countries buying and selling pesticides, while the latter seeks to create uniform standards for maximum levels of pesticide residues among participating countries.Both initiatives operate on a voluntary basis.
Reading and following label directions is required by law in countries such as the United States and in limited parts of the rest of the world.
One study found pesticide self-poisoning the method of choice in one third of suicides worldwide, and recommended, among other things, more restrictions on the types of pesticides that are most harmful to humans.

Uses

Pesticides are used to control organisms considered harmful.

For example,
They are used to kill mosquitoes that can transmit potentially deadly diseases like west nile virus, yellow fever, and malaria. They can also kill bees, wasps or ants that can cause allergic reactions. Insecticides can protect animals from illnesses that can be caused by parasites such as fleas.Pesticides can prevent sickness in humans that could be caused by mouldy food or diseased produce. Herbicides can be used to clear roadside weeds, trees and brush. They can also kill invasive weeds that may cause environmental damage. Herbicides are commonly applied in ponds and lakes to control algae and plants such as water grasses that can interfere with activities like swimming and fishing and cause the water to look or smell unpleasant.Uncontrolled pests such as termites and mould can damage structures such as houses.Pesticides are used in grocery stores and food storage facilities to manage rodents and insects that infest food such as grain. Each use of a pesticide carries some associated risk. Proper pesticide use decreases these associated risks to a level deemed acceptable by pesticide regulatory agencies such as the United States Environmental Protection Agency (EPA) and the Pest Management Regulatory Agency (PMRA) of Canada.
Pesticides can save farmers' money by preventing crop losses to insects and other pests; in the U.S., farmers get an estimated fourfold return on money they spend on pesticides.One study found that not using pesticides reduced crop yields by about 10%.Another study,conducted in 1999, found that a ban on pesticides in the United States may result in a rise of food prices, loss of jobs, and an increase in world hunger.
DDT, sprayed on the walls of houses, is an organochloride that has been used to fight malaria since the 1950s. Recent policy statements by the World Health Organization have given stronger support to this approach.Dr. Arata Kochi, WHO's malaria chief, said, "One of the best tools we have against malaria is indoor residual house spraying. Of the dozen insecticides WHO has approved as safe for house spraying, the most effective is DDT."However, since then, an October 2007 study has linked breast cancer from exposure to DDT prior to puberty.Poisoning may also occur due to use of DDT and other chlorinated hydrocarbons by entering the human food chain when animal tissues are affected. Symptoms include nervous excitement, tremors, convulsions or death. Scientists estimate that DDT and other chemicals in the organophosphate class of pesticides have saved 7 million human lives since 1945 by preventing the transmission of diseases such as malaria, bubonic plague, sleeping sickness, and typhus.However, DDT use is not always effective, as resistance to DDT was identified in Africa as early as 1955, and by 1972 nineteen species of mosquito worldwide were resistant to DDT.A study for the World Health Organization in 2000 from Vietnam established that non-DDT malaria controls were significantly more effective than DDT use.The ecological effect of DDT on organisms is an example of bioaccumulation.

Bethany Richardson, LAc

A pesticide is any substance or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical substance, biological agent (such as a virus or bacterium), antimicrobial, disinfectant or device used against any pest. Pests include insects, plant pathogens, weeds, molluscs, birds, mammals, fish, nematodes (roundworms), and microbes that destroy property, spread disease or are a vector for disease or cause a nuisance. Although there are benefits to the use of pesticides, there are also drawbacks, such as potential toxicity to humans and other animals.

Classification of pesticides

Pesticides can be classified by target organism, chemical structure, and physical state.Pesticides can also be classed as inorganic, synthetic, or biologicals (biopesticides),although the distinction can sometimes blur. Biopesticides include microbial pesticides and biochemical pesticides.Plant-derived pesticides, or "botanicals", have been developing quickly. These include the rotenoids, nicotinoids, and a fourth group that includes strychnine and scilliroside.
Many pesticides can be grouped into chemical families. Prominent insecticide families include organochlorines, organophosphates, and carbamates. Organochlorine hydrocarbons (e.g. DDT) could be separated into dichlorodiphenylethanes, cyclodiene compounds, and other related compounds. They operate by disrupting the sodium/potassium balance of the nerve fiber, forcing the nerve to transmit continuously. Their toxicities vary greatly, but they have been phased out because of their persistence and potential to bioaccumulate.Organophosphate and carbamates largely replaced organochlorines. Both operate through inhibiting the enzyme acetylcholinesterase, allowing acetylcholine to transfer nerve impulses indefinitely and causing a variety of symptoms such as weakness or paralysis. Organophosphates are quite toxic to vertebrates, and have in some cases been replaced by less toxic carbamates. Thiocarbamate and dithiocarbamates are subclasses of carbamates. Prominent families of herbicides include pheoxy and benzoic acid herbicides (e.g. 2,4-D), triazines (e.g. atrazine), ureas (e.g. diuron), and Chloroacetanilides (e.g. alachlor). Phenoxy compounds tend to selectively kill broadleaved weeds rather than grasses. The acetylcholine and benzoic acid herbicides function similar to plant growth hormones, and grow cells without normal cell division, crushing the plants nutrient transport system.[11]:300 Triazines interfere with photsynthesis.[11]:335 Many commonly used pesticides are not included in these families, including glyphosate.

• Algicides or algaecides for the control of algae
• Avicides for the control of birds
• Bactericides for the control of bacteria
• Fungicides for the control of fungi and oomycetes
• Herbicides (e.g. glyphosate) for the control of weeds
• Insecticides (e.g. organochlorines, organophosphates, carbamates, and pyrethroids) for the control of insects - these can be ovicides (substances that kill eggs), larvicides (substances that kill larvae) or adulticides (substances that kill adults)
• Miticides or acaricides for the control of mites
• Molluscicides for the control of slugs and snails
• Nematicides for the control of nematodes
• Rodenticides for the control of rodents
• Virucides for the control of viruses

Pesticides can be classified based upon their biological mechanism function or application method. Most pesticides work by poisoning pests.A systemic pesticide moves inside a plant following absorption by the plant. With insecticides and most fungicides, this movement is usually upward (through the xylem) and outward. Increased efficiency may be a result. Systemic insecticides, which poison pollen and nectar in the flowers, may kill bees and other needed pollinators.
In 2009, the development of a new class of fungicides called paldoxins was announced. These work by taking advantage of natural defense chemicals released by plants called phytoalexins, which fungi then detoxify using enzymes. The paldoxins inhibit the fungi's detoxification enzymes. They are believed to be safer and greener.

History of pesticides

Since before 2000 BC, humans have utilized pesticides to protect their crops. The first known pesticide was elemental sulfur dusting used in ancient Sumer about 4,500 years ago in ancient Mesopotamia. By the 15th century, toxic chemicals such as arsenic, mercury and lead were being applied to crops to kill pests. In the 17th century, nicotine sulfate was extracted from tobacco leaves for use as an insecticide. The 19th century saw the introduction of two more natural pesticides, pyrethrum, which is derived from chrysanthemums, and rotenone, which is derived from the roots of tropical vegetables.Until the 1950s, arsenic-based pesticides were dominant.Paul Müller discovered that DDT was a very effective insecticide. Organochlorines such as DDT were dominant, but they were replaced in the U.S. by organophosphates and carbamates by 1975. Since then, pyrethrin compounds have become the dominant insecticide.Herbicides became common in the 1960s, lead by "triazine and other nitrogen-based compounds, carboxylic acids such as 2,4-dichlorophenoxyacetic acid, and glyphosate". In the 1940s manufacturers began to produce large amounts of synthetic pesticides and their use became widespread.Some sources consider the 1940s and 1950s to have been the start of the "pesticide era."Pesticide use has increased 50-fold since 1950 and 2.3 million tonnes (2.5 million short tons) of industrial pesticides are now used each year.Seventy-five percent of all pesticides in the world are used in developed countries, but use in developing countries is increasing.In 2001 the EPA stopped reporting pesticide use statistics; the only comprehensive study of pesticide use trends was published in 2003 by the National Science Foundation's Center for Integrated Pest Management. In the 1960s, it was discovered that DDT was preventing many fish-eating birds from reproducing, which was a serious threat to biodiversity. Rachel Carson wrote the best-selling book Silent Spring about biological magnification. The agricultural use of DDT is now banned under the Stockholm Convention on Persistent Organic Pollutants, but it is still used in some developing nations to prevent malaria and other tropical diseases by spraying on interior walls to kill or repel mosquitoes.

Pesticides

A pesticide is any substance or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical substance, biological agent (such as a virus or bacterium), antimicrobial, disinfectant or device used against any pest. Pests include insects, plant pathogens, weeds, molluscs, birds, mammals, fish, nematodes (roundworms), and microbes that destroy property, spread disease or are a vector for disease or cause a nuisance. Although there are benefits to the use of pesticides, there are also drawbacks, such as potential toxicity to humans and other animals. FAO has defined the term of pesticide as:
any substance or mixture of substances intended for preventing, destroying or controlling any pest, including vectors of human or animal disease, unwanted species of plants or animals causing harm during or otherwise interfering with the production, processing, storage, transport or marketing of food, agricultural commodities, wood and wood products or animal feedstuffs, or substances which may be administered to animals for the control of insects, arachnids or other pests in or on their bodies. The term includes substances intended for use as a plant growth regulator, defoliant, desiccant or agent for thining fruit or preventing the premature fall of fruit, and substances applied to crops either before or after harvest to protect the commodity from deterioration during storage and transport.

Locomotion & flight

Main article: Insect flight
Basic motion of the insect wing in insect with an indirect flight mechanism scheme of dorsoventral cut through a thorax segment with
a wings
b joints
c dorsoventral muscles
d longitudinal muscles.
Insects are the only group of invertebrates to have developed flight. The evolution of insect wings has been a subject of debate. Some entomologists suggest that the wings are from paranotal lobes, or extensions from the insect's exoskeleton called the nota, called the paranotal theory. Other theories are based on a pleural origin. The pleuron is membrane on the sides of the thorax. These theories include suggestions that wings originated from modified gills, spiracular flaps or as from an appendage of the epicoxa. The epicoxal theory suggests the insect wings are modified epicoxal exites, a modifed appendage at the base of the legs or coxa.In the Carboniferous age, some of the Meganeura dragonflies had as much as a 50 cm (20 in) wide wingspan. The appearance of gigantic insects has been found to be consistent with high atmospheric oxygen. The respiratory system of insects constrains their size, however the high oxygen in the atmosphere allowed larger sizes.The largest flying insects today are much smaller and include several moth species such as the Atlas moth and the White Witch (Thysania agrippina). Insect flight has been a topic of great interest in aerodynamics due partly to the inability of steady-state theories to explain the lift generated by the tiny wings of insects.
Unlike birds, many small insects are swept along by the prevailing winds although many of the larger insects are known to make migration. Aphids, are known to be transported long distances by low-level jet streams.As such, fine line patterns associated with converging winds within weather radar imagery, like the WSR-88D radar network, often represent large groups of insects.

Social behavior & Care of young

A cathedral mound created by termites (Isoptera).
Social insects, such as termites, ants and many bees and wasps, are the most familiar species of eusocial animal.They live together in large well-organized colonies that may be so tightly integrated and genetically similar that the colonies of some species are sometimes considered superorganisms. It is sometimes argued that the various species of honey bee are the only invertebrates (and indeed one of the few non-human groups) to have evolved a system of abstract symbolic communication where a behavior is used to represent and convey specific information about something in the environment. In this communication system, called dance language, the angle at which a bee dances represents a direction relative to the sun, and the length of the dance represents the distance to be flown.
Only insects which live in nests or colonies demonstrate any true capacity for fine-scale spatial orientation or homing. This can allow an insect to return unerringly to a single hole a few millimeters in diameter among thousands of apparently identical holes clustered together, after a trip of up to several kilometers' distance. In a phenomenon known as philopatry, insects that hibernate have shown the ability to recall a specific location up to a year after last viewing the area of interest. A few insects seasonally migrate large distances between different geographic regions (e.g., the overwintering areas of the Monarch butterfly).
Care of young
Most insects lead short lives as adults, and rarely interact with one another except to mate or compete for mates. A small number exhibit some form of parental care, where they will at least guard their eggs, and sometimes continue guarding their offspring until adulthood, and possibly even feeding them. Another simple form of parental care is to construct a nest (a burrow or an actual construction, either of which may be simple or complex), store provisions in it, and lay an egg upon those provisions. The adult does not contact the growing offspring, but it nonetheless does provide food. This sort of care is typical of bees and various types of wasps.

Sound production and hearing

Insects were the earliest organisms to produce and sense sounds. Insects make sounds mostly by mechanical action of appendages. In grasshoppers and crickets, this is achieved by stridulation. Cicadas make the loudest sounds among the insects by producing and amplifying sounds with special modifications to their body and musculature. The African cicada Brevisana brevis has been measured at 106.7 decibels at a distance of 50 cm (20 in).Some insects, such as the hawk moths and Hedylid butterflies, can hear ultrasound and take evasive action when they sense that they have been detected by bats. Some moths produce ultrasonic clicks that were once thought to have a role in jamming bat echolocation. The ultrasonic clicks were subsequently found to be produced mostly by unpalatable moths to warn bats, just as warning colorations are used against predators that hunt by sight.Some otherwise palatable moths have evolved to mimic these calls.
Very low sounds are also produced in various species of Coleoptera, Hymenoptera, Lepidoptera, Mantodea, and Neuroptera. These low sounds are simply the sounds made by the insect's movement. Through microscopic stridulatory structures located on the insect's muscles and joints, the normal sounds of the insect moving are amplified and can be used to warn or communicate with other insects. Most sound-making insects also have tympanal organs that can perceive airborne sounds. Some species in Hemiptera, such as the corixids (water boatmen), are known to communicate via underwater sounds.Most insects are also able to sense vibrations transmitted through surfaces. For example, an insect is caught in a spider web and struggles to escape. The vibrations it produces are sensed by the spider, who is alerted to its presence. Through these vibrations, the spider can tell where on the web the insect is located, as well as how big it is.
Communication using surface-borne vibrational signals is more widespread among insects because of size constraints in producing air-borne sounds. When compared with the size of the insects, communication range can be up to 1000 times the length of the body. So in order to surface-borne vibrational signals, insects of smaller size will use surface-borne vibrational signals, but it is also less diffuse and the signal is confined within the surface and is therefore on one hand easier to locate, but on the other hand is also less likely to attract the predators.Insects cannot effectively produce low-frequency sounds, and high-frequency sounds tend to disperse more in a dense environment (such as foliage), so insects living in such environments communicate primarily using substrate-borne vibrations.Insects use as diverse an array of mechanisms to produce vibration as they do to produce sound.
Some species use vibrations for communicating within members of the same species, such as to attract mates as in the songs of the shield bug Nezara viridula. Vibrations can also be used to communicate between entirely different species; lycaenid (gossamer-winged butterfly) caterpillars which are myrmecophilous (living in a mutualistic association with ants) communicate with ants in this way.The Madagascar hissing cockroach has the ability to press air through its spiracles to make a hissing noise as a sign of aggression;the Death's-head Hawkmoth makes a squeaking noise by forcing air out of their pharynx when agitated, which may also reduce aggressive worker honey bee behavior when the two are in close proximity.

Light production and vision

Insects have compound eyes and two antennae.
A few insects, such as members of the families Poduridae and Onychiuridae (Collembola), Mycetophilidae (Diptera), and the beetle families Lampyridae, Phengodidae, Elateridae and Staphylinidae are bioluminescent. The most familiar group are the fireflies, beetles of the family Lampyridae. Some species are able to control this light generation to produce flashes. The function varies with some species using them to attract mates, while others use them to lure prey. Cave dwelling larvae of Arachnocampa (Mycetophilidae, Fungus gnats) glow to lure small flying insects into sticky strands of silk.Some fireflies of the genus Photuris mimic the flashing of female Photinus species to attract males of that species, which are then captured and devoured.The colors of emitted light vary from dull blue (Orfelia fultoni, Mycetophilidae) to the familiar greens and the rare reds (Phrixothrix tiemanni, Phengodidae).
Most insects, except some species of cave dwelling crickets, are able to perceive light and dark. Many species have acute vision capable of detecting minute movements. The eyes include simple eyes or ocelli as well as compound eyes of varying sizes. Many species are able to detect light in the infrared, ultraviolet and the visible light wavelengths. Color vision has been demonstrated in many species and phylogenetic analysis suggests that UV-green-blue trichromacy existed from at least the Devonian period between 416 and 359 million years ago.

Senses and communication

Many insects possess very sensitive and/or specialized organs of perception. Some insects such as bees can perceive ultraviolet wavelengths, or detect polarized light, while the antennae of male moths can detect the pheromones of female moths over distances of many kilometers.There is a pronounced tendency for there to be a trade-off between visual acuity and chemical or tactile acuity, such that most insects with well-developed eyes have reduced or simple antennae, and vice-versa. There are a variety of different mechanisms by which insects perceive sound, while the patterns are not universal, insects can generally hear sound if they can produce it. Different insect species can have varying hearing, though most insects can hear only a narrow range of frequencies related to the frequency of the sounds they can produce. Mosquitoes have been found to hear up to 2 MHz., and some grasshoppers can hear up to 50 MHz.Certain predatory and parasitic insects can detect the characteristic sounds made by their prey or hosts, respectively. For instance, some nocturnal moths can perceive the ultrasonic emissions of bats, which helps them avoid predation.Insects that feed on blood have special sensory structures that can detect infrared emissions, and use them to home in on their hosts.
Some insects display a rudimentary sense of numbers,such as the solitary wasps that prey upon a single species. The mother wasp lays her eggs in individual cells and provides each egg with a number of live caterpillars on which the young feed when hatched. Some species of wasp always provide five, others twelve, and others as high as twenty-four caterpillars per cell. The number of caterpillars is different among species, but always the same for each sex of larva. The male solitary wasp in the genus Eumenes is smaller than the female, so the mother of one species supplies him with only five caterpillars; the larger female receives ten caterpillars in her cell.

Incomplete metamorphosis

Main article: Hemimetabolism
Insects that show hemimetabolism, or incomplete metamorphosis, change gradually by undergoing a series of molts. An insect molts when it outgrows its exoskeleton, which does not stretch and would otherwise restrict the insect's growth. The molting process begins as the insect's epidermis secretes a new epicuticle. After this new epicuticle is secreted, the epidermis releases a mixture of enzymes that digests the endocuticle and thus detaches the old cuticle. When this stage is complete, the insect makes its body swell by taking in a large quantity of water or air, which makes the old cuticle split along predefined weaknesses where the old exocuticle was thinnest.Other arthropods do not have much a different process and only molt; though must accommodate for the difference in exoskeleton structure and make up with other enzymes.
Immature insects that go through incomplete metamorphosis are called nymphs or in the case of dragonflies and damselflies as naiads. Nymphs are similar in form to the adult
except for the presence of wings, which are not developed until adulthood. With each molt, nymphs grow larger and become more similar in appearance to adult insects.
Like other insects that develop through incomplete metamorphosis, this Southern Hawker dragonfly molts its exoskeleton (shown above) several times during its pre-adult life.
Complete metamorphosis
Main article: Holometabolism
Gulf Fritillary life cycle, an example of holometabolism.
Holometabolism, or complete metamorphosis, is where the insect changes all in four stages, an egg or embryo, a larva, a pupa, and the adult or imago. In these species, egg hatches to produce a larva, which is generally worm-like in form. This worm-like form can be one of several varieties: eruciform (caterpillar-like), scarabaeiform (grub-like), campodeiform (elongated, flattened, and active), elateriform (wireworm-like) or vermiform (maggot-like). The larva grows and eventually becomes a pupa, a stage marked by reduced movement and often sealed within a cocoon. There are three types of pupae: obtect, exarate or coarctate. Obtect pupae are compact, with the legs and other appendages enclosed. Exarate pupae have their legs and other appendages free and extended. Coarctate pupae develop inside the larval skin.Insects undergo considerable change in form during the pupal stage, and emerge as adults. Butterflies are a well known example of an insects that undergo complete metamorphosis, although most insects use this life cycle. Some insects have evolved this system to hypermetamorphosis.
Some of the oldest and most successful insect groups, such Endopterygota, use a system of complete metamorphosis.Strangely though, complete metamorphosis is unique to certain insect orders, like Diptera, Lepidoptera, and Hymenoptera, and no other arthropods undergo it, but incomplete metamorphosis.

Metamorphosis

Metamorphosis :

Metamorphosis in insects is the biological process of development all insects must undergo. There are two forms of metamorphosis: incomplete metamorphosis and complete metamorphosis.

Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some insects, amphibians, mollusks, crustaceans, Cnidarians, echinoderms and tunicates undergo metamorphosis, which is usually accompanied by a change of habitat or behavior.

Scientific usage of the term is exclusive, and is not applied to general aspects of cell growth, including rapid growth spurts. References to "metamorphosis" in mammals are imprecise and only colloquial, but historically idealist ideas of transformation and monadolo as in Goethe's Metamorphosis of Plants, influenced the development of ideas of evolution.

Reproduction and development

Simosyrphus pair:
A pair of Simosyrphus grandicornis hoverflies mating in flight.
The majority of insects hatch from eggs. Some species of insects, like the cockroach Blaptica dubia, are ovoviviparous. The eggs of ovoviviparous animals develop entirely inside the female, and then hatch immediately upon being laid. Some other species, such as those in the genus of cockroaches known as Diploptera, are viviparous, and thus gestate inside the mother and are born alive.Some insects, like parasitic wasps, show polyembryony, where a single fertilized egg divides into many and in some cases thousands of separate embryos.
The different forms of the male (top) and female (bottom) moth Orgyia recens is an example of sexual dimorphism in insects.
Other developmental and reproductive variations include haplodiploidy, polymorphism, paedomorphosis or peramorphosis, sexual dimorphism, parthenogenesis and more rarely hermaphroditism.In haplodiploidy, which is a type of sex-determination system, the offspring's sex is determined by the number of sets of chromosomes an individual receives. This system is typical in bees and wasps.Polymorphism is the where a species may have different morphs or forms, as in the oblong winged katydid, which has four different varieties: green, pink, and yellow or tan. Some insects may retain phenotypes that are normally only seen in juveniles; this is called paedomorphosis. In peramorphosis, an opposite sort of phenomenon, insects take on previously unseen traits after they have matured into adults. Many insects display sexual dimorphism, in which males and females have notably different appearances, such as the moth Orgyia recens as an exemplar of sexual dimorphism in insects.
Some insects use parthenogenesis, a process in which the female can reproduce and give birth without having the eggs fertilized by a male. Many aphids undergo a form of parthenogenesis, called cyclical parthenogenesis, in which they alternate between one or many generations of asexual and sexual reproduction.In summer, aphid is generally female and parthenogenic; in the autumn, males may be produced for sexual reproduction.More rarely, insects display hermaphroditism, in which a given individual has both male and female reproductive organs.
Insect life-histories may show adaptations to withstand cold and dry conditions. Some temperate region insects are capable of activity during winter, while some others may migrate or go into a state of torpor.Still other insects have evolved mechanisms of diapause that allow eggs or pupae to survive these conditions.

Respiration and circulation

Insect respiration is accomplished without lungs. Instead, the insect respiratory system uses a system of internal tubes and sacs through which gases either diffuse or are actively pumped, delivering oxygen directly to tissues that need it via their trachea (element 8 in numbered diagram). Since oxygen is delivered directly, the circulatory system is not used to carry oxygen, and is therefore greatly reduced. The insect circulatory system has no veins or arteries, and instead consists of little more than a single, perforated dorsal tube which pulses peristaltically. Toward the thorax, the dorsal tube (element 14) divides into chambers and acts like the insect's heart. The opposite end of the dorsal tube is like the aorta of the insect circulating the hemolymph, arthropods' fluid analog of blood, inside the body cavity.Air is taken in through openings on the sides of the abdomen called spiracles.
There are many different patterns of gas exchange demonstrated by different groups of insects. Gas exchange patterns in insects can range from continuous and diffusive ventilation, to discontinuous gas exchange.During continuous gas exchange, oxygen is taken in and carbon dioxide is released in a continuous cycle. In discontinuous gas exchange, however, the insect takes in oxygen while it is active and small amounts of carbon dioxide are released when the insect is at rest.Diffusive ventilation is simply a form of continuous gas exchange that occurs by diffusion rather than physically taking in the oxygen. Some species of insect that are submerged also have adaptations to aid in respiration. As larvae, many insects have gills that can extract oxygen dissolved in water, while others need to rise to the water surface to replenish air supplies which may be held or trapped in special structures.

Parts of digestive system

Foregut
Stylized diagram of insect digestive tract showing malpighian tubule, from an insect of the order Orthoptera.
The first section of the alimentary canal is the foregut (element 27 in numbered diagram), or stomodaeum. The foregut is line with a cuticular lining made of chitin and proteins as protection from tough food. The foregut includes the buccal cavity (mouth), pharynx, esophagus, and crop and proventriculus (any part may be highly modified) which both store food and signify when to continue passing onward to the midgut. Here, digestion starts as partially chewed food is broken down by saliva from the salivary glands. As the salivary glands produce fluid and carbohydrate-digesting enzymes (mostly amylases), strong muscles in the pharynx pump fluid into the buccal cavity, lubricating the food like the salivarium does, and helping blood feeders, and xylem and phloem feeders.
From there, the pharynx passes food to the esophagus, which could be just a simple tube passing it on to the crop and proventriculus, and then on ward to the midgut, as in most insects. Alternately, the foregut may expand into a very enlarged crop and proventriculus, or the crop could just be a diverticulum, or fluid filled structure, as in some Diptera species.
Midgut
Once food leaves the crop, it passes to the midgut (element 13 in numbered diagram), also known as the mesenteron, where the majority of digestion takes place. Microscopic projections from the midgut wall, called microvilli, increase the surface area of the wall and allow more nutrients to be absorbed; they tend to be close to the origin of the midgut. In some insects, the role of the microvilli and where they are located may vary. For example, specialized microvilli producing digestive enzymes may more likely be near the end of the midgut, and absorption near the origin or beginning of the midgut.
Hindgut
In the hindgut (element 16 in numbered diagram), or proctodaeum, undigested food particles are joined by uric acid to form fecal pellets. The rectum absorbs 90% of the water in these fecal pellets, and the dry pellet is then eliminated through the anus (element 17), completing the process of digestion. The uric acid is formed using hemolymph waste products diffused from the Malpighian tubules (element 20). It is then emptied directly into the alimentary canal, at the junction between the midgut and hindgut. The number of Malpighian tubules possessed by a given insect varies between species, ranging from only two tubules in some insects to over 100 tubules in others.

Digestive system
An insect uses its digestive system to extract nutrients and other substances from the food it consumes.Most of this food is ingested in the form of macromolecules and other complex substances like proteins, polysaccharides, fats, and nucleic acids. These macromolecules must be broken down by catabolic reactions into smaller molecules like amino acids and simple sugars before being used by cells of the body for energy, growth, or reproduction. This break-down process is known as digestion.
The main structure of an insect's digestive system is a long enclosed tube called the alimentary canal, which runs lengthwise through the body. The alimentary canal directs food unidirectionally from the mouth to the anus. It has three sections, each of which performs a different process of digestion. In addition to the alimentary canal, insects also have paired salivary glands and salivary reservoirs. These structures usually reside in the thorax, adjacent to the foregut.
The salivary glands (element 30 in numbered diagram) in an insect's mouth produce saliva. The salivary ducts lead from the glands to the reservoirs and then forward through the head to an opening called the salivarium, located behind the hypopharynx. By moving its mouthparts (element 32 in numbered diagram) the insect can mix its food with saliva. The mixture of saliva and food then travels through the salivary tubes into the mouth, where it begins to break down.Some insects, like flies, have extra-oral digestion. Insects using extra-oral digestion expel digestive enzymes onto their food to break it down. This strategy allows insects to extract a significant proportion of the available nutrients from the food source.[18]:31 The gut is where almost all of insects' digestion takes place. It can be divided into the foregut, midgut and hindgut.
Insects are an extremely diverse type of animal. All have an external supporting structure, called an exoskleton and all have bodies that can be divided into three major areas: the head, the thorax and the abdomen.
The head carries the eyes, mouthparts and a pair of sensory antenna. The thorax provides support for three pair of legs and usually two pair of wings. Some insects, such as ants and termites, do not have wings. The abdomen contains most of the insect's digestive system and it reproductive organs.
Parts vary greatly by species, but the grasshopper shown above is somewhat representational. On the pages that follow, you will find additional information on heads, legs and wings.

An insect's nervous system is a network of specialized cells (called neurons) that serve as an "information highway" within the body. These cells generate electrical impulses (action potientials) that travel as waves of depolarization along the cell's membrane. Every neuron has a nerve cell body (where the nucleus is found) and filament-like processes (dendrites, axons, or collaterals) that propagate the action potential. Signal transmission is always unidirectional -- moving toward the nerve cell body along a dendrite or a collateral and away from the nerve cell body along an axon.
Neurons are usually divided into three categories, depending on their function within the nervous system:
1. Afferent (sensory) neurons -- these bipolar or multipolar cells have dendrites that are associated with sense organs or receptors. They always carry information toward the central nervous system.
2. Efferent (motor) neurons -- unipolar cells that conduct signals away from the central nervous system and stimulate responses in muscles and glands.
3. Internuncial (association) neurons -- unipolar cells (often with several collaterals and/or branching axons) that conduct signals within the central nervous system.
Individual nerve cells connect with one another through special junctions, called synapses. When a nerve impulse reaches the synapse, it releases a chemical messenger (neurotransmitter substance) that diffuses across the synapse and triggers a new impulse in the dendrite(s) of one or more connecting neurons. Acetylcholine, 5-hydroxytryptamine, dopamine, and noradrenaline are examples of neurotransmitters found in both vertebrate and invertebrate nervous systems.
Nerve cells are typically found grouped in bundles. A nerve is simply a bundle of dendrites or axons that serve the same part of the body. A ganglion is a dense cluster of interconnected neurons that process sensory information or control motor outputs.
The Central Nervous System
Like most other arthropods, insects have a relatively simple central nervous system with a dorsal brain linked to a ventral nerve cord that consists of paired segmental ganglia running along the ventral midline of the thorax and abdomen. Ganglia within each segment are linked to one another by a short medial nerve (commissure) and also joined by intersegmental connectives to ganglia in adjacent body segments. In general, the central nervous system is rather ladder-like in appearance: commissures are the rungs of the ladder and intersegmental connectives are the rails. In more "advanced" insect orders there is a tendency for individual ganglia to combine (both laterally and longitudinally) into larger ganglia that serve multiple body segments.
An insect's brain is a complex of six fused ganglia (three pairs) located dorsally within the head capsule. Each part of the brain controls (innervates) a limited spectrum of activities in the insect's body:
Protocerebrum: The first pair of ganglia are largely associated with vision; they innervate the compound eyes and ocelli.
Deutocerebrum: The second pair of ganglia process sensory information collected by the antennae.
Tritocerebrum: The third pair of ganglia innervate the labrum and integrate sensory inputs from proto- and deutocerebrums. They also link the brain with the rest of the ventral nerve cord and the stomodaeal nervous system (see below) that controls the internal organs. The commissure for the tritocerebrum loops around the digestive system, suggesting that these ganglia were originally located behind the mouth and migrated forward (around the esophagus) during evolution.
Located ventrally in the head capsule (just below the brain and esophagus) is another complex of fused ganglia (jointly called the subesophageal ganglion). Embryologists believe this structure contains neural elements from the three primitive body segments that merged with the head to form mouthparts. In modern insects, the subesophageal ganglion innervates not only mandibles, maxillae, and labium, but also the hypopharynx, salivary glands, and neck muscles. A pair of circumesophageal connectives loop around the digestive system to link the brain and subesophageal complex together.
In the thorax, three pairs of thoracic ganglia (sometimes fused) control locomotion by innervating the legs and wings. Thoracic muscles and sensory receptors are also associated with these ganglia. Similarly, abdominal ganglia control movements of abdominal muscles. Spiracles in both the thorax and abdomen are controlled by a pair of lateral nerves that arise from each segmental ganglion (or by a median ventral nerve that branches to each side). A pair of terminal abdominal ganglia (usually fused to form a large caudal ganglion) innervate the anus, internal and external genitalia, and sensory receptors (such as cerci) located on the insect's back end.

The Stomodaeal Nervous System
An insect's internal organs are largely innervated by a stomodaeal (or stomatogastric) nervous system. A pair of frontal nerves arising near the base of the tritocerebrum link the brain with a frontal ganglion (unpaired) on the anterior wall of the esophagus. This ganglion innervates the pharynx and muscles associated with swallowing. A recurrent nerve along the anterio-dorsal surface of the foregut connects the frontal ganglion with a hypocerebral ganglion that innervates the heart, corpora cardiaca, and portions of the foregut. Gastric nerves arising from the hypocerebral ganglion run posteriorly to ingluvial ganglia (paired) in the abdomen that innervate the hind gut.
In comparison to vertebrates, an insect's nervous system is far more de-centralized. Most overt behavior (e.g. feeding, locomotion, mating, etc.) is integrated and controlled by segmental ganglia instead of the brain. In some cases, the brain may stimulate or inhibit activity in segmental ganglia but these signals are not essential for survival. Indeed, a headless insect may survive for days or weeks (until it dies of starvation or dehydration) as long as the neck is sealed to prevent loss of blood!

Nervous system

The nervous system of an insect can be divided into a brain and a ventral nerve cord. The head capsule, made up of six fused segments, each with a pair of ganglia, or a cluster of nerve cells outside of the brain. The first three pairs of ganglia are fused into the brain, while the three following pairs are fused into a structure of three pairs of ganglia under the insect's esophagus, called the subesophageal ganglion.
The thoracic segments have one ganglion on each side, which are connected into a pair, one pair per segment. This arrangement is also seen in the abdomen but only in the first eight segments. Many species of insects have reduced numbers of ganglia due to fusion or reduction.Some cockroaches have just six ganglia in the abdomen, whereas the wasp Vespa crabro has only two in the thorax and three in the abdomen. Some insects, like the house fly Musca domestica, have all the body ganglia fused into a single large thoracic ganglion.
Insects have nociceptors, cells that detect and transmit sensations of pain.This was discovered in 2003 by studying the variation in reactions of larvae of the common fruitfly Drosophila to the touch of a heated probe and an unheated one. The larvae reacted to the touch of the heated probe with a stereotypical rolling behavior that was not exhibited when the larvae were touched by the unheated probe.Although nociception has been demonstrated in insects, there is not a consensus that insects feel pain consciously.

The insect nervous system consists primarily of a brain (5), located dorsally in the head, and a nerve cord (19) that runs ventrally through the thorax and abdomen. The insect brain is a fusion of three pairs of ganglia, each supplying nerves for specific functions. The first pair, called the protocerebrum, connects to the compound eyes (4) and the ocelli (2, 3) and controls vision. The deutocerebrum innervates the antennae (1). The third pair, the tritocerebrum, controls the labrum, and also connects the brain to the rest of the nervous system.
Below the brain, another set of fused ganglia forms the subesopagheal ganglion (31). Nerves from this ganglion control most of the mouthparts, the salivary glands, and the neck muscles.

The central nerve cord connects the brain and subesophageal ganglion with additional ganglion in the thorax and abdomen. Three pairs of thoracic ganglia (28) innervate the legs, wings, and muscles that control locomotion.

Abdominal ganglia innervate the muscles of the abdomen, the reproductive organs, the anus, and any sensory receptors at the posterior end of the insect.

A separate but connected nervous system called the stomodaeal nervous system innervates most of the body's vital organs. Ganglia in this system control functions of the digestive and circulatory systems. Nerves from the tritocerebrum connect to a ganglia on the esophagus; additional nerves from this ganglia attach to the gut and heart.

Exoskeleton

Their outer skeleton, the cuticle, is made up of two layers: the epicuticle, which is a thin and waxy water resistant outer layer and contains no chitin, and a lower layer called the procuticle. The procuticle is chitinous and much thicker than the epicuticle and has two layers: an outer layer known as the exocuticle and an inner layer known as the endocuticle. The tough and flexible endocuticle is built from numerous layers of fibrous chitin and proteins, criss-crossing each others in a sandwich pattern, while the exocuticle is rigid and hardened.The exocuticle is greatly reduced in many soft-bodied insects (e.g., caterpillars), especially during their larval stages.
Insects are the only invertebrates to have developed flight capability, and this has played an important role in their success.These muscles are able to contract multiple times for each single nerve impulse, allowing the wings to beat faster than would ordinarily be possible. Having their muscles attached to their exoskeletons is more efficient and allows more muscle connections; crustaceans also use the same method, though all spiders use hydraulic pressure to extend their legs, a system inherited from their pre-arthropod ancestors. Unlike insects, though, most aquatic crustaceans are biomineralized with calcium carbonate extracted from the water.

General body plan

Insects possess segmented bodies supported by an exoskeleton, a hard jointed outer covering made mostly of chitin. The segments of the body are organized into three distinctive but interconnected units, or tagmata; a head, a thorax, and an abdomen.The head supports a pair of sensory antennae, a pair of compound eyes, if present, one to three simple eyes or (ocelli) and three sets of variously modified appendages that form the mouthparts. The thorax has six segmented legs (one pair each for the prothorax, mesothorax and the metathorax segments making up the thorax) and two or four wings (if present in the species). The abdomen (made up of eleven segments some of which may be reduced or fused) has most of the digestive, respiratory, excretory and reproductive internal structures.There is considerable variation and many adaptations in the body parts of insects especially wings, legs, antenna, mouth-parts etc.Insects have segmented bodies supported by an exoskeleton, a hard outer covering made mostly of chitin. The segments of the body are organized into three distinctive but interconnected units, or tagmata: a head, a thorax, and an abdomen.[8] The head supports a pair of sensory antennae, a pair of compound eyes, and, if present, one to three simple eyes (or ocelli) and three sets of variously modified appendages that form the mouthparts. The thorax has six segmented legs—one pair each for the prothorax, mesothorax and the metathorax segments making up the thorax—and, if present in the species, two or four wings. The abdomen consists of eleven segments, though in a few species of insects these segments may be fused together or reduced in size. The abdomen also contains most of the digestive, respiratory, excretory and reproductive internal structures.[9]:22–48 There is considerable variation and many adaptations in the body parts of insects especially wings, legs, antenna, mouth-parts etc.


Insect anatomy
A- Head B- Thorax C- Abdomen
1. antenna
2. ocelli (lower)
3. ocelli (upper)
4. compound eye
5. brain (cerebral ganglia)
6. prothorax
7. dorsal blood vessel
8. tracheal tubes (trunk with spiracle)
9. mesothorax
10. metathorax
11. forewing
12. hindwing
13. mid-gut (stomach)
14. dorsal tube (Heart)
15. ovary
16. hind-gut (intestine, rectum & anus)
17. anus
18. oviduct
19. nerve chord (abdominal ganglia)
20. Malpighian tubes
21. tarsal pads
22. claws
23. tarsus
24. tibia
25. femur
26. trochanter
27. fore-gut (crop, gizzard)
28. thoracic ganglion
29. coxa
30. salivary gland
31. subesophageal ganglion
32. mouthparts

Specification

Insects typically move about by walking, flying or occasionally sinking and swimming at the same time. Because it allows for rapid yet stable movement, many insects adopt a tripedal gait in which they walk with their legs touching the ground in alternating triangles. Insects are the only invertebrates to have evolved flight. Many insects spend at least part of their life underwater, with larval adaptations that include gills and some adult insects are aquatic and have adaptations for swimming. Some species, like water striders, are capable of walking on the surface of water.
Insects are mostly solitary, but some insects, such as certain bees, ants, and termites are social and live in large, well-organized colonies. Some insects, like earwigs, show maternal care, guarding their eggs and young. Insects can communicate with each other in a variety of ways. Male moths can sense the pheromones of female moths over distances of many kilometers. Other species communicate with sounds: crickets stridulate, or rub their wings together, to attract a mate and repel other males. Lampyridae in the beetle order Coleoptera communicate with light.
Humans regard certain insects as pests and attempt to control them using insecticides and a host of other techniques. Some insects damage crops by feeding on sap, leaves or fruits, a few bite humans and livestock, alive and dead, to feed on blood and some are capable of transmitting diseases to humans, pets and livestock. Many other insects are considered ecologically beneficial and a few provide direct economic benefit. Silkworms and bees have been domesticated by humans for the production of silk and honey.

Life cycle

The life cycles of insects vary but most hatch from eggs. Insect growth is constrained by the inelastic exoskeleton and development involves a series of molts. The immature stages can differ from the adults in structure, habit and habitat and can include a passive pupal stage in those groups that undergo complete metamorphosis. Insects that undergo incomplete metamorphosis lack a pupal stage and adults develop through a series of nymphal stages.The higher level relationship of the hexapoda is unclear. Fossilized insects of enormous size have been found from the Paleozoic Era, including giant dragonflies with wingspans of 55 to 70 cm (22–28 in). The most diverse insect groups appear to have coevolved with flowering plants.

Define Insect

•small air-breathing arthropod.
•Insects (from insectum, translation of entomon - threaded) are a class within the arthropods that have a chitinous exoskeleton, a three-part body (head, thorax, and abdomen), three pairs of jointed legs, compound eyes, and two antennae. ...
•An arthropod in the class Insecta, characterized by six legs, up to four wings, and a chitinous exoskeleton; Any small arthropod similar to an insect including spiders, centipedes, millipedes, etc; A contemptible or powerless person
•Startled Insects was a British New Wave instrumental jazz group. Their music was a unique mix of experimental synthesizer textures and ethnic rhythms.
•Insects are an alien race in The History of the Galaxy series of novels by Russian science fiction writer Andrey Livadny.

•A type of arthropod in the biological family of insecta; all insects have six legs.
www.pestworldforkids.org/glossary.html
1. Of or pertaining to an insect or insects. [1913 Webster]

2. Like an insect; small; mean; ephemeral. [1913 Webster]

Insect \In"sect\ ([i^]n"s[e^]kt), n. [F. insecte, L. insectum, fr. insectus, p. p. of insecare to cut in. See Section. The name was originally given to certain small animals, whose bodies appear cut in, or almost divided. Cf. Entomology.]
•An arthropod with six legs and a three sectioned body, a head, thorax and abdomen.
a.Any of numerous usually small arthropod animals of the class Insecta, having an adult stage characterized by three pairs of legs and a body segmented into head, thorax, and abdomen and usually having two pairs of wings. Insects include the flies, crickets, mosquitoes, beetles, butterflies, and bees.
b.Any of various similar arthropod animals, such as spiders, centipedes, or ticks. See Regional Note at lightning bug.

what is an insect

Insects (from Latin insectum, a calque of Greek ἔντομον [éntomon], “cut into sections”) are a class within the arthropods that have a chitinous exoskeleton, a three-part body (head, thorax, and abdomen), three pairs of jointed legs, compound eyes, and two antennae. They are among the most diverse group of animals on the planet and include more than a million described species and represent more than half of all known living organisms.The number of extant species is estimated at between six and ten million,and potentially represent over 90% of the differing metazoan life forms on Earth.Insects may be found in nearly all environments, although only a small number of species occur in the oceans, a habitat dominated by another arthropod group, the crustaceans.