Hemimetabolism or hemimetaboly called incomplete metamorphosis and paurometabolism, is the mode of development of certain insects that includes three distinct stages: the egg and the adult stage, or imago. These groups go through gradual changes; the nymph somewhat resembles the adult stage but lacks wings and functional reproductive organs. The Orders that contain hemimetabolous insects are: Hemiptera Orthoptera Mantodea Blattodea Dermaptera Odonata. Phasmatodea Phthiraptera Ephemeroptera Plecoptera Grylloblattodea Thysanoptera In aquatic entomology, different terminology is used when categorizing insects with incomplete metamorphosis. Paurometabolism refers to insects whose nymphs occupy the same environment as the adults, as in the family Gerridae of Hemiptera; the hemimetabolous insects are those whose nymphs, called naiads, occupy aquatic habitats while the adults are terrestrial. This includes all members of the orders Plecoptera and Odonata. Aquatic entomologists use this categorization because it specifies whether the adult will occupy an aquatic or semi aquatic habitat, or will be terrestrial.
This classification system is similar to used nomenclature in terrestrial entomology. Holometabolism Subimago Metamorphosis
Biology is the natural science that studies life and living organisms, including their physical structure, chemical processes, molecular interactions, physiological mechanisms and evolution. Despite the complexity of the science, there are certain unifying concepts that consolidate it into a single, coherent field. Biology recognizes the cell as the basic unit of life, genes as the basic unit of heredity, evolution as the engine that propels the creation and extinction of species. Living organisms are open systems that survive by transforming energy and decreasing their local entropy to maintain a stable and vital condition defined as homeostasis. Sub-disciplines of biology are defined by the research methods employed and the kind of system studied: theoretical biology uses mathematical methods to formulate quantitative models while experimental biology performs empirical experiments to test the validity of proposed theories and understand the mechanisms underlying life and how it appeared and evolved from non-living matter about 4 billion years ago through a gradual increase in the complexity of the system.
See branches of biology. The term biology is derived from the Greek word βίος, bios, "life" and the suffix -λογία, -logia, "study of." The Latin-language form of the term first appeared in 1736 when Swedish scientist Carl Linnaeus used biologi in his Bibliotheca botanica. It was used again in 1766 in a work entitled Philosophiae naturalis sive physicae: tomus III, continens geologian, phytologian generalis, by Michael Christoph Hanov, a disciple of Christian Wolff; the first German use, was in a 1771 translation of Linnaeus' work. In 1797, Theodor Georg August Roose used the term in the preface of a book, Grundzüge der Lehre van der Lebenskraft. Karl Friedrich Burdach used the term in 1800 in a more restricted sense of the study of human beings from a morphological and psychological perspective; the term came into its modern usage with the six-volume treatise Biologie, oder Philosophie der lebenden Natur by Gottfried Reinhold Treviranus, who announced: The objects of our research will be the different forms and manifestations of life, the conditions and laws under which these phenomena occur, the causes through which they have been effected.
The science that concerns itself with these objects we will indicate by the name biology or the doctrine of life. Although modern biology is a recent development, sciences related to and included within it have been studied since ancient times. Natural philosophy was studied as early as the ancient civilizations of Mesopotamia, the Indian subcontinent, China. However, the origins of modern biology and its approach to the study of nature are most traced back to ancient Greece. While the formal study of medicine dates back to Hippocrates, it was Aristotle who contributed most extensively to the development of biology. Important are his History of Animals and other works where he showed naturalist leanings, more empirical works that focused on biological causation and the diversity of life. Aristotle's successor at the Lyceum, wrote a series of books on botany that survived as the most important contribution of antiquity to the plant sciences into the Middle Ages. Scholars of the medieval Islamic world who wrote on biology included al-Jahiz, Al-Dīnawarī, who wrote on botany, Rhazes who wrote on anatomy and physiology.
Medicine was well studied by Islamic scholars working in Greek philosopher traditions, while natural history drew on Aristotelian thought in upholding a fixed hierarchy of life. Biology began to develop and grow with Anton van Leeuwenhoek's dramatic improvement of the microscope, it was that scholars discovered spermatozoa, bacteria and the diversity of microscopic life. Investigations by Jan Swammerdam led to new interest in entomology and helped to develop the basic techniques of microscopic dissection and staining. Advances in microscopy had a profound impact on biological thinking. In the early 19th century, a number of biologists pointed to the central importance of the cell. In 1838, Schleiden and Schwann began promoting the now universal ideas that the basic unit of organisms is the cell and that individual cells have all the characteristics of life, although they opposed the idea that all cells come from the division of other cells. Thanks to the work of Robert Remak and Rudolf Virchow, however, by the 1860s most biologists accepted all three tenets of what came to be known as cell theory.
Meanwhile and classification became the focus of natural historians. Carl Linnaeus published a basic taxonomy for the natural world in 1735, in the 1750s introduced scientific names for all his species. Georges-Louis Leclerc, Comte de Buffon, treated species as artificial categories and living forms as malleable—even suggesting the possibility of common descent. Although he was opposed to evolution, Buffon is a key figure in the history of evolutionary thought. Serious evolutionary thinking originated with the works of Jean-Baptiste Lamarck, the first to present a coherent theory of evolution, he posited that evolution was the result of environmental stress on properties of animals, meaning that the more and rigorously an organ was used, the more complex and efficient it would become, thus adapting the animal to its environment. Lamarck believed that these acquired traits could be passed on to the animal's offspring, who would
Insects or Insecta are hexapod invertebrates and the largest group within the arthropod phylum. Definitions and circumscriptions vary; as used here, the term Insecta is synonymous with Ectognatha. Insects have a chitinous exoskeleton, a three-part body, three pairs of jointed legs, compound eyes and one pair of antennae. Insects are the most diverse group of animals; the total number of extant species is estimated at between ten million. Insects may be found in nearly all environments, although only a small number of species reside in the oceans, which are dominated by another arthropod group, crustaceans. Nearly all insects hatch from eggs. Insect growth is constrained by the inelastic exoskeleton and development involves a series of molts; the immature stages differ from the adults in structure and habitat, can include a passive pupal stage in those groups that undergo four-stage metamorphosis. Insects that undergo three-stage metamorphosis lack a pupal stage and adults develop through a series of nymphal stages.
The higher level relationship of the insects is unclear. Fossilized insects of enormous size have been found from the Paleozoic Era, including giant dragonflies with wingspans of 55 to 70 cm; the most diverse insect groups appear to have coevolved with flowering plants. Adult insects move about by walking, flying, or sometimes swimming; as 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, composed of the front & rear on one side with the middle on the other side. Insects are the only invertebrates to have evolved flight, all flying insects derive from one common ancestor. Many insects spend at least part of their lives under water, with larval adaptations that include gills, some adult insects are aquatic and have adaptations for swimming; some species, such as water striders, are capable of walking on the surface of water. Insects are solitary, but some, such as certain bees and termites, are social and live in large, well-organized colonies.
Some insects, such as 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 great distances. Other species communicate with sounds: crickets stridulate, or rub their wings together, to attract a mate and repel other males. Lampyrid beetles communicate with light. Humans regard certain insects as pests, attempt to control them using insecticides, a host of other techniques; some insects damage crops by feeding on sap, fruits, or wood. Some species are parasitic, may vector diseases; some insects perform complex ecological roles. Insect pollinators are essential to the life cycle of many flowering plant species on which most organisms, including humans, are at least dependent. Many insects are considered ecologically beneficial as predators and a few provide direct economic benefit. Silkworms produce silk and honey bees produce honey and both have been domesticated by humans.
Insects are consumed as food in 80% of the world's nations, by people in 3000 ethnic groups. Human activities have effects on insect biodiversity; the word "insect" comes from the Latin word insectum, meaning "with a notched or divided body", or "cut into", from the neuter singular perfect passive participle of insectare, "to cut into, to cut up", from in- "into" and secare "to cut". A calque of Greek ἔντομον, "cut into sections", Pliny the Elder introduced the Latin designation as a loan-translation of the Greek word ἔντομος or "insect", Aristotle's term for this class of life in reference to their "notched" bodies. "Insect" first appears documented in English in 1601 in Holland's translation of Pliny. Translations of Aristotle's term form the usual word for "insect" in Welsh, Serbo-Croatian, etc; the precise definition of the taxon Insecta and the equivalent English name "insect" varies. In the broadest circumscription, Insecta sensu lato consists of all hexapods. Traditionally, insects defined in this way were divided into "Apterygota" —the wingless insects—and Pterygota—the winged insects.
However, modern phylogenetic studies have shown that "Apterygota" is not monophyletic, so does not form a good taxon. A narrower circumscription restricts insects to those hexapods with external mouthparts, comprises only the last three groups in the table. In this sense, Insecta sensu stricto is equivalent to Ectognatha. In the narrowest circumscription, insects are restricted to hexapods that are either winged or descended from winged ancestors. Insecta sensu strictissimo is equivalent to Pterygota. For the purposes of this article, the middle definition is used; the evolutionary relationship of insects to other animal groups remains unclear. Although traditionally grouped with millipedes and centiped
Ecdysis is the moulting of the cuticle in many invertebrates of the clade Ecdysozoa. Since the cuticle of these animals forms a inelastic exoskeleton, it is shed during growth and a new, larger covering is formed; the remnants of the old, empty exoskeleton are called exuviae. After moulting, an arthropod is described as a callow. Within one or two hours, the cuticle hardens and darkens following a tanning process analogous to the production of leather. During this short phase the animal expands, since growth is otherwise constrained by the rigidity of the exoskeleton. Growth of the limbs and other parts covered by hard exoskeleton is achieved by transfer of body fluids from soft parts before the new skin hardens. A spider with a small abdomen may be undernourished but more has undergone ecdysis; some arthropods large insects with tracheal respiration, expand their new exoskeleton by swallowing or otherwise taking in air. The maturation of the structure and colouration of the new exoskeleton might take days or weeks in a long-lived insect.
Ecdysis allows damaged tissue and missing limbs to be regenerated or re-formed. Complete regeneration may require a series of moults, the stump becoming a little larger with each moult until it is a normal, or near normal, size; the term ecdysis comes from Ancient Greek: ἐκδύω, "to take off, strip off". In preparation for ecdysis, the arthropod becomes inactive for a period of time, undergoing apolysis or separation of the old exoskeleton from the underlying epidermal cells. For most organisms, the resting period is a stage of preparation during which the secretion of fluid from the moulting glands of the epidermal layer and the loosening of the underpart of the cuticle occur. Once the old cuticle has separated from the epidermis, a digesting fluid is secreted into the space between them. However, this fluid remains inactive. By crawling movements, the organism pushes forward in the old integumentary shell, which splits down the back allowing the animal to emerge; this initial crack is caused by a combination of movement and increase in blood pressure within the body, forcing an expansion across its exoskeleton, leading to an eventual crack that allows for certain organisms such as spiders to extricate themselves.
While the old cuticle is being digested, the new layer is secreted. All cuticular structures are shed at ecdysis, including the inner parts of the exoskeleton, which includes terminal linings of the alimentary tract and of the tracheae if they are present; each stage of development between moults for insects in the taxon endopterygota is called an instar, or stadium, each stage between moults of insects in the Exopterygota is called a nymph: there may be up to 15 nymphal stages. Endopterygota tend to have only five instars. Endopterygotes have more alternatives to moulting, such as expansion of the cuticle and collapse of air sacs to allow growth of internal organs; the process of moulting in insects begins with the separation of the cuticle from the underlying epidermal cells and ends with the shedding of the old cuticle. In many species it is initiated by an increase in the hormone ecdysone; this hormone causes: apolysis – the separation of the cuticle from the epidermis secretion of new cuticle materials beneath the old degradation of the old cuticleAfter apolysis the insect is known as a pharate.
Moulting fluid is secreted into the exuvial space between the old cuticle and the epidermis, this contains inactive enzymes which are activated only after the new epicuticle is secreted. This prevents the new procuticle from getting digested; the lower regions of the old cuticle, the endocuticle and mesocuticle, are digested by the enzymes and subsequently absorbed. The exocuticle and epicuticle are hence shed at ecdysis. Spiders change their skin for the first time while still inside the egg sac, the spiderling that emerges broadly resembles the adult; the number of moults varies, both between species and genders, but will be between five times and nine times before the spider reaches maturity. Not since males are smaller than females, the males of many species mature faster and do not undergo ecdysis as many times as the females before maturing. Members of the Mygalomorphae are long-lived, sometimes 20 years or more. Spiders stop feeding at some time before moulting for several days; the physiological processes of releasing the old exoskeleton from the tissues beneath cause various colour changes, such as darkening.
If the old exoskeleton is not too thick it may be possible to see new structures, such as setae, from outside. However, contact between the nerves and the old exoskeleton is maintained until a late stage in the process; the new, teneral exoskeleton has to accommodate a larger frame than the previous instar, while the spider has had to fit into the previous exoskeleton until it has been shed. This means the spider does not fill out the new exoskeleton so it appears somewhat wrinkled. Most species of spiders hang from silk during the entire process, either dangling from a drop line, or fastening their claws into webbed fibres attached to a suitable base; the discarded, dried exoskeleton remains hanging where it was abandoned once the spider has left. To open the old exoskeleton, the spider contracts its abdomen to supply enough fluid to pump into the prosoma with sufficient pressure to crack it open alo
An instar is a developmental stage of arthropods, such as insects, between each moult, until sexual maturity is reached. Arthropods must shed the exoskeleton in order to assume a new form. Differences between instars can be seen in altered body proportions, patterns, changes in the number of body segments or head width. After moulting, i.e. shedding their exoskeleton, the juvenile arthropods continue in their life cycle until they either pupate or moult again. The instar period of growth is fixed; some arthropods can continue to moult after sexual maturity, but the stages between these subsequent moults are not called instars. For most insect species, an instar is the developmental stage of the larval forms of holometabolous or nymphal forms of hemimetabolous insects, but an instar can be any developmental stage including pupa or imago; the number of instars an insect undergoes depends on the species and the environmental conditions, as described for a number of species of Lepidoptera. However it is believed that the number of instars can be physiologically constant per species in some insect orders, as for example Diptera and Hymenoptera.
It should be minded that the number of larval instars is not directly related to speed of development. For instance, environmental conditions may affect the developmental rates of species and still have no impact on the number of larval instars; as examples, lower temperatures and lower humidity slow the rate of development- an example is seen in the lepidopteran tobacco budworm and that may have an effect on how many molts will caterpillars undergo. On the other hand, temperature is demonstrated to affect the development rates of a number of hymenopterans without affecting numbers of instars or larval morphology, as observed in the ensign wasp and in the red imported fire ant. In fact the number of larval instars in ants has been the subject of a number of recent investigations, no instances of temperature-related variation in numbers of instars have yet been recorded; the dictionary definition of instar at Wiktionary
A pupa is the life stage of some insects undergoing transformation between immature and mature stages. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, with four life stages: egg, larva and imago; the processes of entering and completing the pupal stage are controlled by the insect's hormones juvenile hormone, prothoracicotropic hormone, ecdysone. The pupae of different groups of insects have different names such as chrysalis for the pupae of butterflies and tumbler for those of the mosquito family. Pupae may further be enclosed in other structures such as nests, or shells; the pupal stage follows the larval stage and precedes adulthood in insects with complete metamorphosis. The pupa is a non-feeding sessile stage, or active as in mosquitoes, it is during pupation that the adult structures of the insect are formed while the larval structures are broken down. The adult structures grow from imaginal discs. Pupation may last weeks, months, or years, depending on temperature and the species of insect.
For example, pupation lasts eight to fifteen days in monarch butterflies. The pupa may diapause until the appropriate season to emerge as an adult insect. In temperate climates pupae stay dormant during winter, while in the tropics pupae do so during the dry season. Insects emerge from pupae by splitting the pupal case. Most butterflies emerge in the morning. In mosquitoes the emergence is in the night. In fleas the process is triggered by vibrations that indicate the possible presence of a suitable host. Prior to emergence, the adult inside the pupal exoskeleton is termed pharate. Once the pharate adult has eclosed from the pupa, the empty pupal exoskeleton is called an exuvia. In a few taxa of the Lepidoptera Heliconius, pupal mating is an extreme form of reproductive strategy in which the adult male mates with a female pupa about to emerge, or with the newly moulted female. Pupae are immobile and are defenseless. To overcome this, a common strategy is concealed placement. There are some species of Lycaenid butterflies.
Another means of defense by pupae of other species is the capability of making sounds or vibrations to scare potential predators. A few species use chemical defenses including toxic secretions; the pupae of social hymenopterans are protected by adult members of the hive. Based on the presence or absence of articulated mandibles that are employed in emerging from a cocoon or pupal case, the pupae can be classified in to two types: Decticous pupa – pupae with articulated mandibles. Examples are pupae of the orders Neuroptera, Mecoptera and few Lepidoptera families. Adecticous pupa – pupae without articulated mandibles. Examples include orders Strepsiptera, Hymenoptera and Siphonaptera. Based on whether the pupal appendages are free or attached to the body, the pupae can be classified in three types: Exarate pupa – appendages are free and are not encapsulated within a cocoon. All decticous pupa and some adecticous pupa are always exarate.. Obtect pupa – appendages are attached to the body and are encapsulated within a cocoon.
Some adecticous pupa are obtect forms. Coarctate pupa – enclosed in a hardened cuticle of the penultimate larval instar called puparium. However, the pupa itself is of exarate adecticous pupa forms.. A chrysalis or nympha is the pupal stage of butterflies; the term is derived from the metallic gold-coloration found in the pupae of many butterflies, referred to by the Greek term χρυσός for gold. When the caterpillar is grown, it makes a button of silk which it uses to fasten its body to a leaf or a twig; the caterpillar's skin comes off for the final time. Under this old skin is a hard skin called a chrysalis; because chrysalises are showy and are formed in the open, they are the most familiar examples of pupae. Most chrysalides are attached to a surface by a Velcro-like arrangement of a silken pad spun by the caterpillar cemented to the underside of a perch, the cremastral hook or hooks protruding from the rear of the chrysalis or cremaster at the tip of the pupal abdomen by which the caterpillar fixes itself to the pad of silk.
Like other types of pupae, the chrysalis stage in most butterflies is one in which there is little movement. However, some butterfly pupae are capable of moving the abdominal segments to produce sounds or to scare away potential predators. Within the chrysalis and differentiation occur; the adult butterfly emerges from this and expands its wings by pumping haemolymph into the wing veins. Although this sudden and rapid change from pupa to imago is called metamorphosis, metamorphosis is the whole series of changes that an insect undergoes from egg to adult; when emerging, the butterfly uses a liquid, sometimes called cocoonase, which softens the shell of the chrysalis. Additionally, it uses two sharp claws located on the th
Entomology is the scientific study of insects, a branch of zoology. In the past the term "insect" was more vague, the definition of entomology included the study of terrestrial animals in other arthropod groups or other phyla, such as arachnids, earthworms, land snails, slugs; this wider meaning may still be encountered in informal use. Like several of the other fields that are categorized within zoology, entomology is a taxon-based category. Entomology therefore overlaps with a cross-section of topics as diverse as molecular genetics, biomechanics, systematics, developmental biology, ecology and paleontology. At some 1.3 million described species, insects account for more than two-thirds of all known organisms, date back some 400 million years, have many kinds of interactions with humans and other forms of life on earth. Entomology is rooted in nearly all human cultures from prehistoric times in the context of agriculture, but scientific study began only as as the 16th century. William Kirby is considered as the father of Entomology.
In collaboration with William Spence, he published a definitive entomological encyclopedia, Introduction to Entomology, regarded as the subject's foundational text. He helped to found the Royal Entomological Society in London in 1833, one of the earliest such societies in the world. Entomology developed in the 19th and 20th centuries, was studied by large numbers of people, including such notable figures as Charles Darwin, Jean-Henri Fabre, Vladimir Nabokov, Karl von Frisch, two-time Pulitzer Prize winner E. O. Wilson. There has been a history of people becoming entomologists through museum curation and research assistance, such as Sophie Lutterlough at the Smithsonian National Museum of Natural History. Insect identification is an common hobby, with butterflies and dragonflies being the most popular. Most insects can be recognized to order such as Hymenoptera or Coleoptera. However, insects other than Lepidoptera are identifiable to genus or species only through the use of Identification keys and Monographs.
Because the class Insecta contains a large number of species and the characteristics separating them are unfamiliar, subtle, this is very difficult for a specialist. This has led to the development of automated species identification systems targeted on insects, for example, Daisy, ABIS, SPIDA and Draw-wing. In 1994, the Entomological Society of America launched a new professional certification program for the pest control industry called the Associate Certified Entomologist. To qualify as a "true entomologist" an individual would require an advanced degree, with most entomologists pursuing a PhD. While not true entomologists in the traditional sense, individuals who attain the ACE certification may be referred to as ACEs or Associate Certified Entomologists. Many entomologists specialize in a single order or a family of insects, a number of these subspecialties are given their own informal names derived from the scientific name of the group: Coleopterology – beetles Dipterology – flies Odonatology – dragonflies and damselflies Hemipterology – true bugs Isopterology – termites Lepidopterology – moths and butterflies Melittology – bees Myrmecology – ants Orthopterology – grasshoppers, etc.
Trichopterology – caddis flies Vespology – Social wasps Like other scientific specialties, entomologists have a number of local and international organizations. There are many organizations specializing in specific subareas. Amateur Entomologists' Society Deutsches Entomologisches Institut Entomological Society of America Entomological Society of Canada Entomological Society of Japan Entomologischer Verein Krefeld Entomological Society of India International Union for the Study of Social Insects Netherlands Entomological Society Royal Belgian Entomological Society Royal Entomological Society of London Société entomologique de France Here is a list of selected museums which contain large insect collections. Zoological survey of India National Pusa Collection, Division of Entomology, Indian Agricultural Research Institute, New Delhi, India Pakistan Museum of Natural History Garden Avenue, Islamabad, Pakistan Natal Museum, South Africa Muséum national d'histoire naturelle, France Museum für Naturkunde, Germany Kelvingrove Art Gallery, Scotland Natural History Museum, Budapest Hungarian Natural History Museum Natural History Museum, Geneva Natural History Museum, the Netherlands Natural History Museum, United Kingdom Natural History Museum, Oslo Norway Natural History Museum, St. Petersburg Zoological Collection of the Russian Academy of Science Naturhistorisches Museum, Austria Oxford University Museum of Natural History, Oxford Royal Museum for Central Africa, Belgium Swedish Museum of Natural History, Sweden The Bavarian State Collection of Zoology Zoologische Staatssammlung München World Museum Liverpool, the Bug House Academy of Natural Sciences of Philadelphia American Museum of Natural History, New York City Auburn University Museum of Natural History, Ala