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Origin of Insects

Insects are highly specialized group of invertebrates belonging to the largest animal Phyla, the ARTHROPODA, which also includes in it, the prawns, crabs, lobsters, centipedes, millipedes, scorpions, ticks, mites and spiders. Practically three fourth of the animal species come under this phylum.

The Arthropods evolved during Cambrian period from primitive annelidan ancestor. The main evolutionary stem of Arthropod is represented by the Crustacia- Insecta- Myriapoda.

The insects originated in the Devonian period of Palaeozoic era. Diplura and Thysanura are the most primitive wingless insects while mayflies, damselflies, dragonflies and stoneflies represent the primitive winged insects.

Evolution

Evolution is a process whereby population are altered over a period of time and may split into separate branches, hybridize together or terminate by extinction.

Nomenclature should not be confused with terminology which deals with terms, like antenna, abdomen, radius etc. Names of animal and plants may be either vernacular or scientific.

Vernacular names or local names of plants and animals are different from region to region, from language to language.

Scientific names or Latin or International names are used universally all over the world. Without them we would not be able to communicate and to use the knowledge accumulated about animals and plants in literature. These international names are under certain rules or nomenclature.

Nomenclature

No-men-cla-ture means a system of names. It is derived from Latin Nomen means name and calor means to call, which means to call by names. Nomenclature is the “language of Zoology” and the rules of nomenclature are its grammar. Since all zoologists work with animals and used their names, it is essential that the general principles of zoological nomenclature be familiar to all zoologists.

Classification

Classification is ordering of organisms into groups (or sets) on the basis of their relationships that are of associations by contiguity, similarity or both.

Classification of living things is an attempt to interpret nature. It attempts to bring together the kinds that are alike and closely related and to separate those that are unlike and unrelated.

Animals might be classified in various ways but the classification is based primarily on structural characters. Those animals with certain structures in common are classified into one group, and those with other structures into other group. Thus the animal kingdom is divided into a dozen or so major groups called phyla (singular, phylum); each phylum has a name, and its members have certain structural characters in common. The characters used to distinguish phyla include the number of cells, symmetry, body form and segmentation, the nature of the appendages, and the arrangement of the internal organs.

On the basis of degree of complexity, and probably evolutionary sequence, the animal phyla are usually arranged in a series from the lower phyla to the higher ones.

The foundation of modern insect classification was laid by Brauer in 1885. According to Brauer insects were classified as Subclass: Apterygogenea (pterous) and Pterygogenea (winged) based on:

• Presence or absence of wings.

• Mouthparts.

• Metamorphosis.

• Number of Malpighian tubules.

• The nature of wings.

• Thoracic segments etc.

The earliest classification of insects was based on habits and habitats and on certain gross anatomical features that define the general aspects of different kinds. In classifying insects, not only anatomical characters but also facts pertaining to physiology, biology, distribution, ecology and sometime cytology of the species is taken into consideration.

Origin of systematics is as old as Vedas (1500 BC), Ramayana (1900 BC), Mahabharat (1400 BC) and Upanisad (350 BC) in which mention had been made about various animals.

History of Insect Classification

Linnaeus (1758-1766) in the 12th edition of Systema Naturae, divided insects into 9 orders

1. Coleoptera (earwigs – Dermeptera).

2. Orthoptera.

3. Hemiptera.

4. Lepidoptera.

5. Neuroptera (ant lion, Sialis, termites and dragon flies).

6. Hymenoptera

7. Diptera.

8. Thysanoptera.

9. Aptera (wingless insects, spiders, scorpions, terrestrial crustacians and Myriapods).

The science of taxonomy started with Linnaeus, who used two Latin names for an organism by a universally agreed name and identity, and further provided means for their realistic classification. These identifications and classifications got strengthened further with accumulated biological knowledge. In the recent times taxonomy has become more demanding subject for areas in entomology, which are dependent on access to accumulated experience and knowledge for their survival and development. By providing name and classifying an insect, taxonomy provides information on the nature of population, life cycle, habitat and behaviour and thereby developing hypotheses, concepts and theories, which are basic to biological control. In addition, it enables comparison and synthesis, all of which lead to refinement and fine tuning of the concepts and theories for identification.

Man has tendency to classify everything in a hierarchical manner for example, ships may be classified on size, weight, what they carry or naval versus merchant or passenger. Any of these classification is as valid as any other.

But classification of biological species is unusual in that a predefined system exists i.e. the evolutionary relationships among organisms. But evolutionary relationships can only be estimated; and contrary to popular belief, even a good fossil record does not conclusively show the phylogeny or evolutionary tree of a group species.

Numerical taxonomy can be defined as “Numerical evaluation of the affinity or similarity between taxonomic units and ordering of these units into taxa on the basis of their affinities”. The term includes drawing of phylogenetic inferences from the data by statistical or other mathematical methods to the extent to which this should prove possible. The practice involves a number of fundamental assumptions and philosophical attitudes toward taxonomic work.

The Species Concept in Systematics

The modern biological or, more strictly, genetical concept of a species is a group of interbreeding organisms, genetically isolated from other such groups. The definition of the category species has long been one of the major problems of taxonomy. It is because of two reasons:

1. Because of the congruity of lingering typological concepts with the nature of evolving species.

2. Because evolutionary species may have changing characters and are only gradually differentiated in phylogeny.

For evolutionary study and descriptive purposes, many kinds of variation within species come in to consideration, but the only regular intra specific taxon is the subspecies. Subspecies are widely but not universally useful and their definitions yield to the same sort of criteria as for dividing other phylogentic continuance.

Super Species

According to Mayr (1931, 1942) Linsleg and Usinger (1953),“A super Species is a monophyletic group of very closely related and largely or entirely allopatric Species”.

Super species are, in other words, groups of populations that seem on other grounds (morphology, ecology etc.) to have passed beyond the point of potential interbreeding and to have acquired separate evolutionary roles. They are so by the more conclusive evidence of remaining separate when sympatric. It is to be assumed that they are still near the critical point of specification, near a definitive isolation. They are nascent species that will, if they survive, collectively form a subgenus or eventually a genus but have hardly get reached that degree of divergence.

They are not given special names; the Rules of Nomenclature make no provision for that usual designation and they are mostly known by the name of an included species and are in fact super species.

Identification of the insects is the integral part of systematics. It utilises all taxonomic procedures. The collections in the world are the accumulation of past taxonomists and are stored for the future identifications. Every species name is based on a published description or figure and usually on the type specimen. Identification is the association of other specimens with the appropriate description or with type specimen.

The steps in identification are as follows:

1. Preliminary key to orders and families

2. Key to genera and species if recent monographs or faunal works are available

3. Reference to the most recent catalogues

4. Reference to current bibliographies for literature published subsequent to the most recent catalogues

5. Reference to original descriptions

6. Comparison with the authentic described specimens or with types.

Taxonomic keys are devices that make identification of taxa easy and enjoyable. A key is presentation of appropriate diagnostic characters in a series of attractive choices to facilitate identification of a specimen.

Key characters are the characters that are easily perceived of very low variability, usually present in preserved material. They are useful as convenient labels for distinguishing taxa by the process of classification. Many taxonomic characters such as chemical, chromosomal, physiological and behavioural may have high value of identification because they are inaccessible in preserved material. Ideal key characters apply equally to all individuals of the population. They are absolute, relatively constant and external so that they can be observed directly without special equipment.

Code of Ethics was observed by International Commission on Zoological Nomenclature for renaming of homonyms. The commission had issues declarations or opinions from time to time, which together constitute the start of a code of ethics in the field of nomenclature. The first Declaration of the international Commission was as follows:

• When it is noticed by any zoologist that the generic name or specific name published by any living author as new is in reality a homonym, and therefore unavailable under articles 34 and 36 of the Rules of Nomenclature, the action is for said person to notify the said author of the facts, and give said author an opportunity to propose a substitute name.

• When the author of a newly discovered generic or specific homonym is dead, the discoverer is free to rename the genus or species as he likes. It is common practice to rename the category after the author of the homonym. However, this practice was never universal and it is not a matter of ethics.

Classification involves grouping organisms into a series of hierarchical categories. Actual method of establishing a classification consists in defining groups or categories on a hierarchical scale. The animals can be classified in a taxonomic hierarchy consisting of a series of categories of ascending ranks from species to kingdom. Each of these categories includes one or more groups from the next lower level. Therefore, all animals can be classified in a taxonomic hierarchy consisting a series of categories in ascending order from species to kingdom such as species, genus, family, order, class, phylum and kingdom.

According to the history of biological classification, Aristotle, a Greek philosopher classified different animals based on the habitat, characteristics etc. Later Swedish botanist Carolus Linnaeus introduced taxonomic hierarchy categories during 18th century and this system is followed globally.

Taxonomic hierarchy refers to the sequence of categories in increasing or decreasing order. Kingdom is the highest rank and species is the lowest rank in hierarchy. Taxonomic hierarchy is the process of arranging various organisms into successive levels of biological classification. Each of the level of the hierarchy is called taxonomic category or rank.

Palaeontology is the science that deals with the life past geological periods. It is just the opposite of neontology which deals with the systematics of recent organisms. Fossils are the remains or parts of animal or plants that lived thousands of years ago which have turned into rock. They are preserved traces of living organisms in the earth crust.

Fossil History of Insects

Occurrence of insects in fossilised state provides a clear idea of the main order of insects. The oldest known insects’ fossil appears to be of Apterygota and blattids seem to be the oldest living insects, which have almost lived without undergoing large scale evolutionary changes from the Carboniferous to the present day.

Some of the earliest apterygotes might have developed from the Permian or lower Carboniferous. The richest collection of fossil insects is from the vegetable deposits like coal, lignite peats and in amber entangled in the raisin. Most of the insects are known only through their wings, resulting in the study of venation. However, the amber fossil of Miocene presents a clearer picture. The best known epoch is undoubtedly the Permian while Triassic provides richest discoveries of the insect fossils.

The study of science is incomplete, if it is not made available to others. The most popular way to make the work wide circulated is through publication. It is most important for taxonomists that what is most needed in the world about their work, is to be published in time. In taxonomy, the publications may be in the form of book, pamphlets, journals, articles, scientific papers, symposium chapters, catalogues and check-lists etc. A taxonomist should publish his work in appropriate journals like population studies or biological studies etc. It should be mentioned in the title if the new research is published. Sometimes, new taxa of one country are included in the faunal work of another country without mention in the title about the country. This is bound to remain out of knowledge for future works. The major types of taxonomic publications are as follows:

Publication of New Taxa

These are ordinary descriptive papers of new taxa such as subspecies and genera. Such descriptions do not involve careful comparison of all related species. The published descriptions may be justified only when the names of the taxa are required for biological or economic works. These are also helpful in revision of any work where the new species can be easily fitted in the classification. In addition to this, short communications concerning with new records of various taxa are also quite useful.

Hybridisation

Hybridisation occurs when two species cross to form a new species. If they are named before their hybrid nature has become apparent, the names would become invalid as soon as the hybridity of the specimen has been established.

Hybridism can be of three types:

1. Sympatric Hybridisation

When individuals in two regions overlap in an otherwise well-defined species, they are called sympatric hybridisation. This is common in bird of paradise and humming birds. This hybridisation is listed as cross of two parental species.

Insects are present everywhere. In the world where life is possible, insects can be found. To begin with, it is not necessary to go to distant places. Insects can be collected from garden, cultivated fields or even in our house. For the collection of insects, we must have some idea of the following:

1. How they live.

2. What they require at different stages of life.

A. Complete Metamorphosis

There are four stages

A database is a collection of data, typically describing the activities of one or more related organisations. Biological database is meant for storing and organising biological data, collecting information from life sciences, scientific experiments, computational analysis and contents from published literatures.

Biological databases play a vital role in bioinformatics, since it helps varieties of researchers to access and analyse data from different parts of the world. The knowledge obtained helps to solve disease oriented and environment related issues and to make vital policy decisions. Biological databases remain as tool to identify insect species as well as in comparing their relationships with related species. The biological knowledge distributed among different general and specialised databases, can be retrieved with efficient queries.

Various information like genomics, proteomics, metabolomics, microarray, genes expression, phylogenetics etc. are also stored and maintained as biological databases in terms of genome databases, protein structure databases, taxonomic database etc. These computerised web databases facilitate effective data management and analysis help in knowledge transmission, make coherent information exchange between the studies and public audience.

Pests

The English name ‘Pest’ is derived from the Latin word ‘Pestis’, which means causing destruction. Pests are defined as ‘those organisms, which compete with man in his food supply, damage his possessions and attack himself’. They are of vital concern to mankind in their everyday life, as they cause considerable damage directly as well as indirectly to crops, domestic animals, birds and to man himself. They are also responsible for causing or transmitting many serious diseases. Pests include thousands of invertebrates such as, insects, nematodes, mites, ticks, snails and slugs, crabs etc. and vertebrates such as, rats, squirrels, jackals, pigs and boars, porcupines, rabbits, deers, bats, some species of birds etc., which are destructive to plants and livestock. Several microorganisms such as, fungi, bacteria, viruses, mycoplasma, phytoplasma etc. are also pests in nature. Weeds and phanerogamic parasites are also pests in the true sense.

‘Insect pest control’ includes all measures adopted to make the life of insects hard and ultimately to destroy them or to prevent their multiplication and spread. Such measures can be taken up before the appearance of the pests or after occurrence of the pests. To achieve this purpose , it is quite necessary to know the factors, which favor the occurrence of the pests and acquire enough knowledge about the nature and life cycle of the pests, the vulnerable growth stage at which they can be effectively destroyed and appropriate measures of control to destroy them Control measures may be either preventive or direct.

Need for pest control

Control measures for the control of pests have to be taken up as soon as the infestation reaches the economic threshold level. Failure to control the pests at this stage will result in further increase in the pest population and consequent loss in yield and economic loss.

The need for pest control is of two kinds :

i) For yield maximization. The only objective of pest control in this method is to maximize the yield. The cost incurred for pest control is most often more than the income accrued as a result of pest control. The method is adopted only with the object of increasing the yield as much as possible so that the country and the people may be benefited. In this method, pest control operations are taken up before the actual occurrence of the pest or before the pest infestation reaches the economic threshold level. Such treatments taken up to control the pests before their occurrence are known as ‘prophylactic treatments’