Insects are a class of arthropods that have a hard exoskeleton, a three-part body (head, thorax, and abdomen), three pairs of jointed legs, compound eyes, and two antennae. They are the most diverse group of animals on the planet and include more than a million described species. Insects represent more than half of all known living organisms.[2][3] The number of extant species is estimated at between six and ten million,[2][4][5] and potentially represent over 90% of the differing life forms on Earth.[6] 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.
Although insects use several different birth strategies, most are born by hatching from eggs. Insects undergo one of two types of metamorphosis during their lives. Insects that use incomplete metamorphosis, like dragonflies, develop through a series of molts. Alternatively, some insects like butterflies only molt once in their lives in a process known as complete metamorphosis. The relationship of insects' evolutionary history to that of other animals is unclear, though evidence has emerged indicating that insects and crustaceans may have shared common ancestors. 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), much larger than any living insect. Many highly successful insect groups are shown to have coevolved with flowering plants.
Insects typically move about by walking, flying or occasionally swimming. 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 lives underwater, and some have developed the ability to swim. Some species, like water striders, are even capable of walking on the surface of water.
Insects are mostly solitary, but some insects, such as certain species of bees, ants, and termites are social and live together in large, well-organized colonies. Some insects, like earwigs, care for their young. Humans regard certain insects as pests and attempt to control them using insecticide. Some insects are parasitic, and some are damaging to agriculture. Many insects are capable of transmitting diseases. On the other hand, insects such as butterflies and bees are beneficial to the environment and to agriculture through pollination, and insects such as silkworms and bees have been domesticated by humans for the production of silk and honey. Insects can communicate in a variety of ways. Male moths can sense the pheromones of female moths over distances of many kilometres. Other species communicate with sounds: crickets stridulate, or rub their legs together, to attract a mate and repel other males.[7]
Morphology
Insect anatomy
A- Head
B- Thorax
C- Abdomen
Insects' body parts, any of them in fact, can be highly developed or adapted among different species, though most 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
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.[9]:57
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.[10] 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.[11] This was discovered in 2003 by studying the variation in reactions of Drosophila larvae 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.[12] In a report to the Norwegian Scientific Committee for Food Safety, Lauritz Sømme wrote that while insects "have the capacity to detect and respond to noxious or averse stimuli", they are unable to feel the conscious experience of pain.[13]
Digestive system
An insect uses its digestive system to extract nutrients and other substances from the food it consumes.[14] 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.[9]:70–77
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.[14][15] 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.[16]:31
Sections of the gut
The gut is where almost all of insects' digestion takes place. It can be divided into the foregut, midgut and hindgut.
Foregut
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.[9]:70
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.[9]:70 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.[16]:30-31
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.[16]:32
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). The uric acid 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. [9]:71–72, 78–80
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 insects 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.[9]:61–65[17] 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.[9]:65–68 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.[18] 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.[19][20]
Exoskeleton
Scanning electron micrograph of a
thrips (Thysanoptera), showing fine structure, the compound eyes, wing construction, and setae
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.[9]:22–24 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.[9]:186 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 mucles connections, crustaceans also use the same method, though all spiders use hydraulic pressure to extend them, a system inherited from their pre-arthropod ancestors. Unlike insects, though, most aquatic crustaceans are biomineralized with calcium carbonate extracted from the water.[21][22]
Reproduction and development
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 live.[9]:129, 131, 134–135 Some insects, like parasitic wasps, show polyembryony, where a single fertilized egg divides into many and in some cases thousands of separate embryos.[9]:136–137
The different form 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.[9]:143 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.[23] Polymorphism is the where a species may have different morphs or forms, as in the oblong winged katydid, which has three different varieties: green, pink, and yellow or tan. Some insects may retain phenotypes and genotypes 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. The moth Orgyia recens is an exemplar of sexual dimorphism in insects.
Some insects use parthenogenesis, where the female can reproduce and give birth without fertilization by males. Many aphids undergo a form of parthenogenesis, called cyclical parthenogenesis, in which they alternate between one or many generations of asexual and sexual reproduction.[24][25] More rarely, insects display hermaphroditism, in which a given individual has both male and female reproductive organs.
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.
Incomplete metamorphosis
Insects that show hemimetabolism, or incomplete metamorphosis, change gradually by undergoing a series of molts. An insect molts when it outgrow 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.[9]:142[26] 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 are called nymphs and are similar in form to the adult except for the presence of wings, which are not developed until adulthood. With each molting, nymphs grow larger and become more similar in appearance to adult insects.
Complete metamorphosis
Holometabolism, or complete metamorphosis, is where the insect changes all in four stages, an egg or embryo, a larva, a pupa, and the adult. 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.[9]:151 Insects undergo considerable change in form during the pupal stage, and emerge as adults, or imago. Butterflies are an example of an insect that undergoes complete metamorphosis. Some insects have even evolved hypermetamorphosis.
Some of the oldest and most successful insect groups, such Endopterygota, use a system of complete metamorphosis.[9]:143 Strangely though, complete metamorphosis is unique to certain insect orders, like Diptera, Lepidoptera, and Hymenoptera, and no other arthropods undergo it, but incomplete metamorphosis.
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 kilometres.[27] 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. Like mosquitoes have been found to hear up to 2 MHz., and yet some grasshoppers can hear up to 50 MHz.[28] 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.[9]:87–94 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,[29] 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.
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.[30] 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.[31] The colors of emitted light vary from dull blue (Orfelia fultoni, Mycetophilidae) to the familiar greens and the rare reds (Phrixothrix tiemanni, Phengodidae).[32]
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.[33]
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).[34] 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.[35] Some otherwise palatable moths have evolved to mimic these calls.[36]
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 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.[9]:87–94
Communication using surface-borne vibrational signals is more widespread among insects because of size constraints in producing air-borne sounds.[37] 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.[38] The mechanisms of production of vibrational signals are just as diverse as those for producing sound in insects.
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.[39] Vibrations can also be used to communicate between entirely different species, such as between ants and myrmecophilous lycaenid caterpillars.[40] The Madagascar hissing cockroach has the ability to press air through its spiracles to make a hissing noise, and the Death's-head Hawkmoth makes a squeaking noise by forcing air out of their pharynx.
Chemical communication
In addition to the use of sound for communication, a wide range of insects have evolved chemical means for communication. These chemicals, termed semiochemicals, are often derived from plant metabolites include those meant to attract, repel and provide other kinds of information. Pheromones, a type of semiochemical, are used for attracting mates of the opposite sex, for aggregating conspecific individuals of both sexes, for deterring other individuals from approaching, to mark a trail, and to trigger aggression in nearby individuals. Allomones benefit their producer by the effect they have upon the receiver. Kairomones benefit their receiver instead of their producer. Synomones benefit the producer and the receiver. While some chemicals are targeted at individuals of the same species, others are used for communication across species. The use of scents is especially well known to have developed in social insects.[9]:96–105
Social behavior
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.[41] 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.[9]:309–311
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 millimetres in diameter among thousands of apparently identical holes clustered together, after a trip of up to several kilometres' 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.[42] A few insects seasonally migrate large distances between different geographic regions (e.g., the overwintering areas of the Monarch butterfly).[43]
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.[44]
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; others have suggested they are modified epicoxal exits, or exits on the insect's legs or coxa, called the Epicoxal theory. 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 percentage of oxygen in the atmosphere found from ice core-samples was as high as 35% compared to the current 21%. The respiratory system of insects constrains their size, however the high oxygen in the atmosphere allowed larger sizes.[45] 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, insects are swept along by the prevailing winds.[46] This includes aphids, which are often transported long distances by low-level jet streams.[47] 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.[48]
Walking
Many adult insects use six legs for walking and have adopted a tripedal gait. The tripedal gait allows for rapid walking while always having a stable stance and has been studied extensively in cockroaches. The legs are used in alternate triangles touching the ground. For the first step, the middle right leg and the front and rear left legs are in contact with the ground and move the insect forward, while the front and rear right leg and the middle left leg are lifted and moved forward to a new position. When they touch the ground to form a new stable triangle the other legs can be lifted and brought forward in turn and so on.[49] The purest form of the tripedal gait is seen in insects moving at high speeds. However, this type of locomotion is not rigid and insects can adapt a variety of gaits. For example, when moving slowly, turning, or avoiding obstacles, four or more feet may be touching the ground. Insects can also adapt their gait to cope with the loss of one or more limbs.
Cockroaches are among the fastest insect runners and, at full speed, adopt a bipedal run to reach a high velocity in proportion to their body size. As cockroaches move very quickly, they need to be video recorded at several hundred frames per second to reveal their gait. More sedate locomotion is also studied by scientists in stick insects like Phasmatodea. A few insects have evolved to walk on the surface of the water, especially the bugs of the Gerridae family, commonly known as water striders. A few species of ocean-skaters in the genus Halobates even live on the surface of open oceans, a habitat that has few insect species.
Use in robotics
Insect walking is of particular interest as an alternative form of locomotion in robots. The study of insects and bipeds has a significant impact on possible robotic methods of transport. This may allow new robots to be designed that can traverse terrain that robots with wheels may be unable to handle.[49]
Swimming
The backswimmer
Notonecta glauca underwater, showing its paddle-like hindleg adaptation
A large number of insects live either parts or the whole of their lives underwater. In many of the more primitive orders of insect, the immature stages are spent in an aquatic environment. Some groups of insects, like certain water beetles, have aquatic adults as well.[19]
Many of these species have adaptations to help in under-water locomotion. Water beetles and water bugs have legs adapted into paddle-like structures. Dragonfly naiads use jet propulsion, forcibly expelling water out of their rectal chamber.[50] Some species like the water striders are capable of walking on the surface of water. They can do this because their claws are not at the tips of the legs as in most insects, but recessed in a special groove further up the leg; this prevents the claws from piercing the water's surface film.[19] Other insects such as the Rove beetle Stenus are known to emit salivary secretions that reduce surface tension making it possible for them to move on the surface of water by Marangoni propulsion (also known by the German term Entspannungsschwimmen).[51][52]
Evolution
Evolution has produced astonishing variety in insects. Pictured are some of the possible shapes of
antennae.
The evolutionary relationships of insects to other animal groups remain unclear. Although more traditionally grouped with millipedes and centipedes, evidence has emerged favoring closer evolutionary ties with crustaceans. In the Pancrustacea theory, insects, together with Remipedia and Malacostraca, make up a natural clade.[53] Other terrestrial arthropods, such as centipedes, millipedes, scorpions and spiders, are sometimes confused with insects since their body plans can appear similar, sharing (as do all arthropods) a jointed exoskeleton. However upon closer examination their features differ significantly; most noticeably they do not have the six legs characteristic of adult insects.[54]
The higher-level phylogeny of the arthropods continues to be a matter of debate and research. In 2008, researchers at Tufts University uncovered what they believe is the world's oldest known full-body impression of a primitive flying insect, a 300 million-year-old specimen from the Carboniferous Period.[56] The oldest definitive insect fossil is the Devonian Rhyniognatha hirsti, from the 396 million year old Rhynie chert. This species already possessed dicondylic mandibles (two articulations in the mandible), a feature associated with winged insects, suggesting that wings may already have evolved at this time. Thus, the first insects probably appeared earlier, in the Silurian period.[1][57]
The origins of insect flight remain obscure, since the earliest winged insects currently known appear to have been capable fliers. Some extinct insects had an additional pair of winglets attaching to the first segment of the thorax, for a total of three pairs. As of 2009, there is no evidence that suggests that the insects were a particularly successful group of animals before they evolved to have wings.[58]
Late Carboniferous and Early Permian insect orders include both extant groups and a number of Paleozoic species, now extinct. During this era, some giant dragonfly-like forms reached wingspans of 55 to 70 cm, (22–28 in) making them far larger than any living insect. This gigantism may have been due to higher atmospheric oxygen levels that allowed increased respiratory efficiency relative to today. The lack of flying vertebrates could have been another factor. Most extinct orders of insects developed during the Permian era that began around 270 million years ago. Many of the early groups became extinct during the Permian-Triassic extinction event, the largest mass extinction in the history of the Earth, around 252 million years ago.[59]
The remarkably successful Hymenopterans appeared as long as 146 million years ago in the Cretaceous era, but achieved their wide diversity more recently in the Cenozoic era, which began 66 million years ago. A number of highly-successful insect groups evolved in conjunction with flowering plants, a powerful illustration of coevolution.[60]
Many modern insect genera developed during the Cenozoic. Insects from this period on are often found preserved in amber, often in perfect condition. The body plan, or morphology, of such specimens is thus easily compared with modern species. The study of fossilized insects is called paleoentomology.
Coevolution
Insects were among the earliest terrestrial herbivores and acted as major selection agents on plants.[60] Plants evolved chemical defenses against this herbivory and the insects in turn evolved mechanisms to deal with plant toxins. Many insects make use of these toxins to protect themselves from their predators. Such insects often advertise their toxicity using warning colors.[60] This successful evolutionary pattern has also been utilized by mimics. Over time, this has led to complex groups of coevolved species. Conversely, some interactions between plants and insects, like pollination, are beneficial to both organisms. Coevolution has led to the development of very specific mutualisms in such systems.
Classification
|
| Classification |
|
|
|
| Insecta |
|
| Dicondylia |
|
| Pterygota |
|
| Neoptera |
| -Blattodea - 3,684–4,000 |
| -Coleoptera - 360,000–400,000 |
| -Dermaptera - 1,816 |
| -Diptera - 152,956 |
| -Embioptera - 200–300 |
| -Grylloblattaria - 24 |
| -Hymenoptera - 115,000 |
| -Lepidoptera - 174,250 |
| -Mantodea - 2,200 |
| -Mecoptera - 481 |
| -Megaloptera - 250–300 |
| -Neuroptera - ~5,000 |
| -Orthoptera - 24,380 |
| -Phasmatodea - 2,500–3,300 |
| -Phthiraptera - >3,000–~3,200 |
| -Plecoptera - 2,274 |
| -Siphonaptera - 2,525 |
| -Strepsiptera - 596 |
| -Trichoptera - 12,627 |
| -Zoraptera - 28 |
| -Zygentoma - 370 |
|
|
Traditional morphology-based or look-based systematics has included in Hexapoda, usually given the rank of superclass,[9]:180 four groups: insects (Ectognatha), springtails (Collembola), Protura and Diplura, the latter three being grouped together as Entognatha on the basis of internalized mouth parts. Supraordinal relationships have undergone numerous changes with the advent of methods based on evolutionary history and genetic data. A recent theory is that Hexapoda is polyphyletic, or where the last common ancestor was not a member of the group, with the entognath classes having separate evolutionary histories from Insecta.[62] As many of the traditional look-based taxa have been shown to be paraphyletic, so not using taxa like subclass, superorder and infraorder and rather on monophyletic groupings: groupings with one common ancestor for taxa have proven to be better. The following list represents the best supported monophyletic groupings for the Insecta.
Insects can be divided into two groups historically treated as subclasses: wingless insects, known as Apterygota, and winged insects, known as Pterygota. The Apterygota consist of two primitively wingless orders: bristletails (Archaeognatha) and silverfish (Thysanura). Archaeognatha make up the Monocondylia based on the shape of their mandibles, while Thysanura and Pterygota are grouped together as Dicondylia. It is possible that the Thysanura themselves are not monophyletic, with the family Lepidotrichidae a sister group to the Dicondylia (Pterygota and the remaining Thysanura).[63][64]
Paleoptera and Neoptera are the winged orders of insects separated by the presence of hardened body parts called sclerites; also, in Neoptera, muscles that allow their wings to fold flatly over the abdomen. Neoptera can further be divided into incomplete metamorphosis-based (Polyneoptera and Paraneoptera) and complete metamorphosis-based groups. It has been proven hard to make clear of the relationships between the orders in Polyneoptera because of the constant new findings, and changing of the taxa based on them. For example, Paraneoptera has turned out to be more closely related to Endopterygota than to the rest of the Exopterygota. The recent molecular finding that the traditional louse orders Mallophaga and Anoplura are derived from within Psocoptera has led to the new taxon Psocodea.[65] Phasmatodea and Embiidina have been suggested to form Eukinolabia.[66] Mantodea, Blattodea & Isoptera are thought to form a monophyletic group termed Dictyoptera.[67]
It is likely that Exopterygota is paraphyletic in regards to Endopterygota. Matters that have had a lot of controversy include Strepsiptera and Diptera grouped together as Halteria based on a reduction of one of the wing pairs – a position not well-supported in the entomological community.[68] The Neuropterida are often lumped or split on the whims of the taxonomist. Fleas are now thought to be closely related to boreid mecopterans.[69] Many questions remain to be answered when it comes to basal relationships amongst endopterygote orders, particularly Hymenoptera.
The study of the classification or taxonomy of any insect is called systemic entomology. Normally, if one chooses to work with a more specific order or even a family, the systemics would be added to the study of that order or family, an example would be systemic dipterology.
Relationship to humans
Main article:
Insect ecologyMany insects are considered pests by humans. Insects commonly regarded as pests include those that are parasitic (mosquitoes, lice, bed bugs), transmit diseases (mosquitoes, flies), damage structures (termites), or destroy agricultural goods (locusts, weevils). Many entomologists are involved in various forms of pest control, as in research for companies to produce insecticides, but increasingly relying on methods of biocontrol. Biocontrol is arguably better, as it uses more environmentally friendly options, unlike most insecticides.[70][71]
Despite the large amount of effort focused at controlling insects, human attempts to kill pests with insecticides can backfire. If used carelessly the poison can kill all kinds of organisms in the area, including insects' natural predators such as birds, mice, and other insectivores. The effects of DDT's use exemplifies how some insecticides can threaten wildlife beyond intended populations of pest insects.[72][73]
Because they help flowering plants to
cross-pollinate, some insects are critical to agriculture. This
European honey bee is gathering nectar while pollen collects on its body.
Although pest insects attract the most attention, many insects are beneficial to the environment and to humans. Some insects, like wasps, bees, butterflies, and ants, pollinate flowering plants. Pollination is a mutualistic relationship between plants and insects. As insects gather nectar from different plants of the same species, they also spread pollen from plants on which they have previously fed. This greatly increases plants' ability to cross-pollinate, which maintains and possibly even improves their evolutionary fitness. This is ultimately affects humans since ensuring healthy crops is critical to agriculture. A serious environmental problem is the decline of populations of pollinator insects, and a number of species of insects are now cultured primarily for pollination management in order to have sufficient pollinators in the field, orchard or greenhouse at bloom time.[74]:240-243 Insects also produce useful substances such as honey, wax, lacquer and silk. Honey bees have been cultured by humans for thousands of years for honey, although contracting for crop pollination is becoming more significant for beekeepers. The silkworm has greatly affected human history, as silk-driven trade established relationships between China and the rest of the world.
In some cultures, insects, especially deep-fried cicadas, are considered to be delicacies, and in fact have a high protein content for their mass. In most first-world countries, however, the consumption of insects is taboo.[75] Despite this disposition, peoples in these cultures tend to accidentally consume between 50 and 90 insects in a given year. Fly larvae (maggots) were formerly used to treat wounds to prevent or stop gangrene, as they would only consume dead flesh. This treatment is finding modern usage in some hospitals. Adult insects, such as crickets, and insect larvae of various kinds are also commonly used as fishing bait.[76] In some parts of the world, insects are used for human food, while being a taboo in other places. There are proponents of developing this use to provide a major source of protein in human nutrition.[9]:10–13 Since it is impossible to entirely eliminate pest insects from the human food chain, insects are present in many foods, especially grains. Food safety laws in many countries do not prohibit insect parts in food, but rather limit the quantity. According to cultural materialist anthropologist Marvin Harris, the eating of insects is taboo in cultures that have other protein sources such as fish or livestock.
Insectivorous insects, or insects which feed on other insects, are beneficial to humans because they eat insects that could cause damage to agriculture and human structures. For example, aphids feed on crops and cause problems for farmers, but ladybugs feed on aphids, and can be used as a means to get significantly reduce pest aphid populations. While birds are perhaps more visible predators of insects, insects themselves account for the vast majority of insect consumption. Without predators to keep them in check, insects can undergo almost unstoppable population explosions.[9]:328–348[9]:400[77][78]
Many insects, especially beetles, are scavengers that feed on dead animals and fallen trees and thereby recycle biological materials into forms found useful by other organisms. Insects are responsible for much of the process by which topsoil is created.[9]:3, 218–228 The ancient Egyptian religion considered dung beetles sacred, and represented them as beetle-shaped amulets, or scarabs. Dung beetles have been used in countries including Australia as an agent of biological pest control to reduce the populations of pestilent flies and parasitic worms. The Australian Dung Beetle Project successfully introduced 23 species of dung beetle, including Onthophagus gazella and Euoniticellus intermedius from South Africa and Europe. This resulting in a 90% reduction in bush flies as well as improved soil fertility and quality.[79]
In genetic and biological research, Drosophila melanogaster, the common fruit fly, is considered to be among the first and most widely used. Today, D. melanogaster is the best genetically understood of all eukaryotic organisms with its complete genome sequenced and first published in 2000, curated at the FlyBase database.[80] All organisms use the same system of cell reproduction; therefore, understanding processes such as transcription and replication in fruit flies helps in understanding these processes in other eukaryotes, including humans.[81]
See also
References
- ^ a b Engel, Michael S.; David A. Grimaldi (2004). "New light shed on the oldest insect". Nature 427: 627–630. doi:10.1038/nature02291. http://www.nature.com/nature/journal/v427/n6975/full/nature02291.html.
- ^ a b Chapman, A. D. (2006). Numbers of living species in Australia and the World. Canberra: Australian Biological Resources Study. pp. 60pp. ISBN 978-0-642-56850-2. http://www.deh.gov.au/biodiversity/abrs/publications/other/species-numbers/index.html.
- ^ Wilson, E.O.. "Threats to Global Diversity". http://www.globalchange.umich.edu/globalchange2/current/lectures/biodiversity/biodiversity.html. Retrieved 2009-05-17.
- ^ Vojtech Novotny, Yves Basset, Scott E. Miller, George D. Weiblen, Birgitta Bremer, Lukas Cizek & Pavel Drozd (2002). "Low host specificity of herbivorous insects in a tropical forest". Nature 416: 841–844. doi:10.1038/416841a.
- ^ a b Erwin, Terry L. (1997). Biodiversity at its utmost: Tropical Forest Beetles. pp. 27–40. In: Reaka-Kudla, M. L., D. E. Wilson & E. O. Wilson (eds.). Biodiversity II. Joseph Henry Press, Washington, D.C..
- ^ Erwin, Terry L. (1982). "Tropical forests: their richness in Coleoptera and other arthropod species". Coleopt. Bull. 36: 74–75.
- ^ Hack, Mace A. (November, 1998). "The Energetics of Male Mating Strategies in Field Crickets (Orthoptera: Gryllinae: Gryllidae)". Journal of Insect Behavior (Springer Netherlands) 11 (Volume 11, Number 6): 853-867. ISSN 0892-7553. http://www.springerlink.com/content/p71l3q7g52v18321/.
- ^ "O. Orkin Insect zoo". The University of Nebraska Department of Entomology. http://insectzoo.msstate.edu/Students/basic.structure.html. Retrieved 2009-05-03.
- ^ a b c d e f g h i j k l m n o p q r s t u v w x y Gullan, P.J.; P.S. Cranston (2005). The Insects: An Outline of Entomology (3 ed.). Oxford: Blackwell Publishing. ISBN 1-4051-1113-5.
- ^ Schneiderman, Howard A. (1960). "Discontinuous respiration in insects: role of the spiracles". Biol. Bull. (119): 494–528. http://www.biolbull.org/cgi/reprint/119/3/494?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=insect+thoracic+spiracle&andorexactfulltext=and&searchid=1&FIRSTINDEX=0&sortspec=relevance&resourcetype=HWCIT.
- ^ Eisemann, WK et al (1984). "Do insects feel pain? — A biological view". Cellular and Molecular Life Sciences 40: 1420–1423.
- ^ Tracey, J et al (18 April 2003). "painless, a Drosophila gene essential for nociception". Cell 113 (2): 261–273. doi:10.1016/S0092-8674(03)00272-1. PMID 12705873.
- ^ Sømme, LS (14 January 2005). "Sentience and pain in invertebrates". Norwegian Scientific Committee for Food Safety. http://74.125.155.132/scholar?q=cache:dbrbM20yEQ4J:scholar.google.com/&hl=en. Retrieved September 30, 2009.
- ^ a b "General Entomology - Digestive and Excritory system". NC state University. http://www.cals.ncsu.edu/course/ent425/library/tutorials/internal_anatomy/digestive.html. Retrieved 2009-05-03.
- ^ Duncan, Carl D. (1939). A Contribution to The Biology of North American Vespine Wasps (1 ed.). Stanford: Stanford University Press. pp. 24–29.
- ^ a b c Nation, James L. (November 2001). "15". Insect Physiology and Biochemistry (1 ed.). CRC Press. pp. 496pp. ISBN 0849311810. http://books.google.com/books?id=l3v2tOvz1uQC&pg=PA31&dq=insect+foregut#v=onepage&q=insect%20foregut&f=false.
- ^ Meyer, John R. (17 February 2006). "Circulatory System". NC State University: Department of Entomology, NC State University. pp. 1. http://www.cals.ncsu.edu/course/ent425/tutorial/circulatory.html. Retrieved 2009-10-11.
- ^ Chown, S.L.; S.W. Nicholson (2004). Insect Physiological Ecology. New York: Oxford University Press. ISBN 0198515499.
- ^ a b c Richard W. Merritt, Kenneth W. Cummins, and Martin B. Berg (editors) (2007). An Introduction to the Aquatic Insects of North America (4th ed.). Kendall Hunt Publishers. ISBN 9780757550492.
- ^ Merritt, RW, KW Cummins, and MB Berg (2007). An Introduction To The Aquatic Insects Of North America. Kendall Hunt Publishing Company. ISBN 0-7575-4128-3.
- ^ Barnes, R.S.K., Calow, P., Olive, P., Golding, D., and Spicer, J. (2001), "Invertebrates with Legs: the Arthropods and Similar Groups", The Invertebrates: A Synthesis, Blackwell Publishing, p. 168, ISBN 0632047615, http://books.google.co.uk/books?id=TBMsbe9efPgC&pg=PA168&dq=arthropod+hydraulic&sig=ACfU3U2CPJ_K9DDSTNMoj97Mutbl8DFLgg, retrieved 2008-09-25
- ^ Lowenstam, H.A., and Weiner, S. (1989), On biomineralization, Oxford University Press US, p. 111, ISBN 0195049772, http://books.google.co.uk/books?id=JbAgy0AAopsC&dq=arthropod+biomineralization&lr=&source=gbs_summary_s&cad=0, retrieved 2008-09-25
- ^ William O. H. Hughes, Benjamin P. Oldroyd, Madeleine Beekman, Francis L. W. Ratnieks (2008-05-30). "Ancestral Monogamy Shows Kin Selection Is Key to the Evolution of Eusociality" (html). Science (American Association for the Advancement of Science) 320 (5880): 1213–1216. doi:10.1126/science.1156108. http://www.sciencemag.org/cgi/content/abstract/320/5880/1213. Retrieved 2008-08-04.
- ^ Effect of nitrogen fertilization on Aphis gossypii (Homoptera: Aphididae): variation in size, color, and reproduction, E. Nevo and M. Coll, J. Econ. Entomol. 94: 27-32, 2001.
- ^ Effect of nitrogen fertilizer on the intrinsic rate of increase of the rusty plum aphid, Hysteroneura setariae (Thomas) (Homoptera: Aphididae) on rice (Oryza sativa L.), G. C. Jahn, L. P. Almazan, and J. Pacia, Environmental Entomology 34 (4): 938-943, 2005.
- ^ Ruppert, E.E., Fox, R.S., and Barnes, R.D. (2004), Invertebrate Zoology (7 ed.), Brooks / Cole, pp. 523–524, ISBN 0030259827
- ^ "Insects". Alien Life Forms. pp. 4. http://crazydaz.com/insects.pdf. Retrieved 2009-05-17.
- ^ Cator, L. J. et al (20 February 2009). "Harmonic Convergence in the Love Songs of the Dengue Vector Mosquito". Science 323 (5917): 1077-1079. doi:10.1126/science.1166541.
- ^ Möller, R. (2002) (in German). A Biorobotics Approach to the Study of Insect Visual Homing Strategies. pp. pg.11. http://www.ti.uni-bielefeld.de/downloads/publications/habil.pdf.
- ^ Pugsley, Chris W. (1983). "Literature review of the New Zealand glowworm Arachnocampa luminosa (Diptera: Keroplatidae) and related cave-dwelling Diptera". New Zealand Entomologist 7 (4): 419–424. http://www.ento.org.nz/nzentomologist/free_issues/NZEnto07_4_1983/Volume%207-4-419-424.pdf.
- ^ Lloyd, James E. (1984). "Occurrence of Aggressive Mimicry in Fireflies". The Florida Entomologist 67 (3): 368–376. doi:10.2307/3494715.
- ^ Lloyd, James E.; Erin C. Gentry (2003). The Encyclopedia of Insects. Academic Press. pp. 115–120. ISBN 0125869908.
- ^ Briscoe, AD & L Chittka (2001). "The evolution of color vision in insects". Annu. Rev. Entomol 46: 471–510. doi:10.1146/annurev.ento.46.1.471.
- ^ Walker, T.J., ed. 2001. University of Florida Book of Insect Records, 2001. [1]
- ^ Hristov, N.I.; Conner, W.E. (2005). "Sound strategy: acoustic aposematism in the bat–tiger moth arms race". Naturwissenschaften 92: 164–169. doi:10.1007/s00114-005-0611-7.
- ^ Barber, J. R.; W. E. Conner (2007). "Acoustic mimicry in a predator–prey interaction". Proc. Nat. Acad. Sci. 104 (22): 9331–9334. doi:10.1073/pnas.0703627104. PMID 17517637. http://www.pnas.org/cgi/content/figsonly/104/22/9331.
- ^ Virant-Doberlet, M.; Čokl A. (2004). "Vibrational communication in insects". Neotropical Entomology 33 (2): 121–134. doi:10.1590/S1519-566X2004000200001. http://www.scielo.br/pdf/ne/v33n2/a01v33n2.pdf.
- ^ Bennet-Clark, H.C. (1998). "Size and scale effects as constraints in insect sound communication". Phil. Trans. R. Soc. Lond. B 353: 407–419. doi:10.1098/rstb.1998.0219.
- ^ Miklas, Nadège; Nataša Stritih, Andrej Čokl, Meta Virant-Doberlet, Michel Renou (2001). "The Influence of Substrate on Male Responsiveness to the Female Calling Song in Nezara viridula". Journal of Insect Behavior 14 (3): 313–332. doi:10.1023/A:1011115111592.
- ^ DeVries, P. J. (1990). "Enhancement of symbiosis between butterfly caterpillars and ants by vibrational communication". Science 248: 1104–1106. doi:10.1126/science.248.4959.1104. PMID 17733373.
- ^ Brewer, Gary. "Social insects". North Dakota State University. http://www.ndsu.nodak.edu/entomology/topics/societies.htm. Retrieved 2009-05-06.
- ^ Salt, R.W. (January 1961). "Principles of Insect Cold-Hardiness". Annual Review of Entomology (Lethbirdge, Alberta, Canada: Canada Agriculture Research Station). http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.en.06.010161.000415.
- ^ Oberhauser, Karen S.; Solensky, Michelle (June 2004). "27". in Michelle Solensky. The Monarch Butterfly. 1 (1 ed.). Cornell University: Cornell University Press. pp. 248. ISBN 0801441889.
- ^ "Social Insects". North Dakota State University. http://www.ndsu.nodak.edu/entomology/topics/societies.htm. Retrieved 2009-10-12.
- ^ Dudley, R. (1998). "Atmospheric oxygen, giant Paleozoic insects and the evolution of aerial locomotor performance". Journal of Experimental Biology 201 (8): 1043–1050. http://jeb.biologists.org/cgi/reprint/201/8/1043.pdf.
- ^ Diana Yates (2008). Birds migrate together at night in dispersed flocks, new study indicates. University of Illinois at Urbana - Champaign. Retrieved on 2009-04-26.
- ^ Drake, V. A.; R. A. Farrow (1988). "The Influence of Atmospheric Structure and Motions on Insect Migration". Annual Review of Entomology 33: 183–210. doi:10.1146/annurev.en.33.010188.001151.
- ^ Bart Geerts and Dave Leon (2003). P5A.6 Fine-Scale Vertical Structure of a Cold Front As Revealed By Airborne 95 GHZ Radar. University of Wyoming. Retrieved on 2009-04-26.
- ^ a b Biewener, Andrew A (2003). Animal Locomotion. Oxford University Press. ISBN 0-19-850022-X.
- ^ Mill, P. J.; R. S. Pickard (1975). "Jet-propulsion in anisopteran dragonfly larvae". Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology 97 (4): 329–338. doi:10.1007/BF00631969.
- ^ Linsenmair, K.; Jander R. (1976). "Das "entspannungsschwimmen" von Velia and Stenus". Naturwissenschaften 50: 231. doi:10.1007/BF00639292.
- ^ Bush, J. W. M.; David L. Hu (2006). "Walking on Water: Biolocomotion at the Interface". Annu. Rev. Fluid Mech. 38: 339–369. doi:10.1146/annurev.fluid.38.050304.092157. http://www.cims.nyu.edu/~dhu/Pubweb/Bush_Hu_06.pdf.
- ^ "Palaeos invertebrates:Arthropoda". Palaeos Invertebrates. 2002-05-03. http://www.palaeos.com/Invertebrates/Arthropods/Pancrustacea.html. Retrieved 2009-05-06.
- ^ "Evolution of insect flight". Malcolm W. Browne. 1994-10-25. http://dml.cmnh.org/1994Oct/msg00116.html. Retrieved 2009-05-06.
- ^ "Tree of Life Web Project. Version 01 January 1995 (temporary) of Arthropoda". Tree of Life Web Project. 1995. http://www.tolweb.org/Arthropoda. Retrieved 2009-05-09.
- ^ "Researchers Discover Oldest Fossil Impression of a Flying Insect". Newswise. http://newswise.com/articles/view/545296/. Retrieved 2008-19-20.
- ^ Rice, C. M., Ashcroft, W. A., Batten, D. J., Boyce, A. J., Caulfield, J. B. D., Fallick, A. E., Hole, M. J., Jones, E., Pearson, M. J., Rogers, G., Saxton, J. M., Stuart, F. M., Trewin, N. H. & Turner, G. (1995). "A Devonian auriferous hot spring system, Rhynie, Scotland". Journal of the Geological Society, London 152: 229–250. doi:10.1144/gsjgs.152.2.0229.
- ^ Grimaldi, D. and Engel, M.S. (2005). Evolution of the Insects. Cambridge University Press. ISBN 0-521-82149-5.
- ^ Rasnitsyn, A.P. and Quicke, D.L.J. (2002). History of Insects. Kluwer Academic Publishers. ISBN 1-4020-0026-X.
- ^ a b c J. Stein Carter (2005-03-29). "Coevolution and Pollination". University of Cincinnati. http://biology.clc.uc.edu/courses/bio303/coevolution.htm. Retrieved 2009-05-09.
- ^ Tree of Life Web Project (2002). "Insecta". http://www.tolweb.org/Insecta/8205. Retrieved 2009-05-12.
- ^ David A. Kendall (2009). "Classification of Insect". http://www.kendall-bioresearch.co.uk/class.htm. Retrieved 2009-05-09.
- ^ Gilliott, Cedric (August 1995). Entomology (2 ed.). Springer-Verlag New York, LLC. pp. 820pp. ISBN 0306449676. http://books.google.com/books?id=DrTKxvZq_IcC&pg=PA96&dq=Insect+classification+based+on+winged+and+wingless#v=onepage&q=Insect%20classification%20based%20on%20winged%20and%20wingless&f=false.
- ^ Kapoor, V.C. C. (January 1998). Principles and Practices of Animal Taxonomy. 1 (1 ed.). Science Publishers. pp. 48. ISBN 157808024X.
- ^ Johnson, K. P., Yoshizawa, K. and V. S. Smith. 2004. Multiple origins of parasitism in lice. Proceedings of the Royal Society of London 271: 1771–1776.
- ^ Terry, M. D. and M. F. Whiting. 2005. Mantophasmatodea and phylogeny of the lower neopterous insects. Cladistics 21(3): 240–257
- ^ "Evidence from multiple gene sequences indicates that termites evolved from wood-feeding cockroaches.". E Current Biology 10(13): 801–804. 2000.
- ^ Bonneton, F., F. G. Brunet, J. Kathirithamby, V. Laudet. 2006. The rapid divergence of the ecdysone receptor is a synapomorphy for Mecopterida that clarifies the Strepsiptera problem. Insect Molecular Biology 15(3):351–362.
- ^ Whiting, M.F. 2002. Mecoptera is paraphyletic: multiple genes and phylogeny of Mecoptera and Siphonaptera. Zoologica Scripta 31(1): 93–104.
- ^ "Beneficial Insects, Mites and Organisms". Biocontrol Network. http://www.biconet.com/biocontrol.html. Retrieved 2009-05-06.
- ^ Davidson, E. (2006). Big Fleas Have Little Fleas: How Discoveries of Invertebrate Diseases Are Advancing Modern Science. ISBN 0-8165-2544-7.
- ^ Colborn, T; vom Saal, FS; Soto, AM (October 1993). "Developmental effects of endocrine-disrupting chemicals in wildlife and humans". Environmental Health Perspectives 101 (5): 378–384. PMID 8080506.
- ^ Nakamaru, M; Iwasab first2=Y; Nakanishic, J (October 2003). "Extinction risk to bird populations caused by DDT exposure". Chemosphere 53 (4): 377-387. doi:10.1016/S0045-6535(03)00010-9. PMID 12946395.
- ^ Smith, Deborah T (December 1991). Agriculture and the Environment: The 1991 Yearbook of Agriculture (1991 ed.). United States Government Printing. pp. 191 pp.. ISBN 0160341442. http://books.google.com/books?id=fDTbAAAAMAAJ&q=insects+pollinate&dq=insects+pollinate.
- ^ Michels, John (1880). John Michels. ed. Science. 1. American Association for the Advance of Science. 229 Broadway ave., N.Y.: American Association for the Advance of Science. pp. 2090pp. http://books.google.com/books?id=aDkLAAAAYAAJ&pg=PA69&dq=Insects+also+produce+useful+substances+honey+silk#v=onepage&q=Insects%20also%20produce%20useful%20substances%20honey%20silk&f=false.
- ^ Sherman, Ronald A.; Pechter, Edward A. (13 December 1987). "Maggot therapy: a review of the therapeutic applications of fly larvae in human medicine, especially for treating osteomyelitis". Medical and Veterinary Entomology (Journal compilation © 2009 The Royal Entomological Society) 2 (3): Pages 225 - 230. http://www3.interscience.wiley.com/journal/119457073/abstract.
- ^ "Biocontrol Network - Beneficial Insects". Biocontrol Network. http://www.biconet.com/biocontrol.html. Retrieved 2009-05-09.
- ^ Davidson, RH and William F. Lyon (1979). Insect Pests of Farm, Garden, and Orchard. Wiley, John & Sons, Incorporated. p. 38. ISBN 0-471-86314-9.
- ^ Bornemissza, G. F. (1976), The Australian dung beetle project 1965-1975, Australian Meat Research Committee Review 30:1–30
- ^ Adams MD, Celniker SE, Holt RA, et al. (2000). "The genome sequence of Drosophila melanogaster". Science 287 (5461): 2185–95. doi:10.1126/science.287.5461.2185. PMID 10731132. http://www.sciencemag.org/cgi/content/abstract/287/5461/2185. Retrieved 2007-05-25.
- ^ Pierce, Benjamin A. Genetics: A conceptual Approach. 2nd edition
External links
