Here is an essay on ‘Insects’ for class 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Insects’ especially written for school and college students.
Essay on Insects
Essay # 1. Origin and Importance of Insects:
Insects are generally considered the most successful group of living organisms on Earth. Success may be attributed to mobility, high reproductive rates, short life cycles, the ability to change body form during their life (metamorphosis), and their adaptive nature. Many insects have the ability to fly during part of their life cycle, making it possible to disperse to new habitats.
Because of their small size, even insects that do not fly may effectively move to new habitat by being windblown, attached to animals, or transported by human commerce. They produce from hundreds to thousands of offspring, per female.
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Some species have the ability to-reproduce without sex (called asexual or parthenogenic reproduction); in some species males are not known to exist. The life span of insects varies from days to years. Often hatching of young is timed to the availability of food. The ability to change body form during the life span of many groups of insects has allowed for specialization of young and adults.
Often, the young are highly adaptive to exploiting food sources that may be limited, and the adults are adaptive to disperse to new resources that can be exploited by the next generation. A resting stage (pupa) occurs in many insects; this is a period of low activity.
This allows the insect to undergo extreme physiological and morphological changes that result in emergence of the adult stage. The pupal stage may also allow the insect to pass through adverse conditions in protected areas such as leaf litter and soil without exhausting energy.
As a group, feeding habits of insects are highly variable. Their adaptive nature may best be realized by noting that insects are found in all of Earth’s ecosystems except the oceans (although some species are found in the fur of ocean-faring mammals). Insects include those that feed on living and decaying plant and animal matter.
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Leaf, stem, and root tissue may be eaten by the many kinds of plant feeders. Processed plant material, such as stored products and wooden structures, are a food source for many plant feeding species.
Plant-feeding insects may be considered beneficial if they specialize in eating weedy species or if feeding, actually benefits the plant (e.g., pollen “feeding” by insects, which results in pollination, is a major reason why flowering plants are so successful). Other species are beneficial because they feed on dead plant material (decomposers).
The feeding habits of animal feeders are as varied as those of plant feeders. Animal feeders may specialize on the internal organs of living animals (endoparasites) or the skin, hair, and feathers (ectoparasites). Humans are also attacked by selected species.
Animal feeders include beneficial insects that are predators or parasites of insects and other arthropods. Other beneficial animal feeding insects feed on dead animal tissue (decomposers) and animal waste (dung feeders).
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There are more species of insects than all other animals and plants combined; approximately 750,000 species have been described, over 87,000 of which are in North America. Current estimates put the total number of insect species at 2 million, although some authorities believe that up to 30 million species may exist.
Among these, there are about 600 species in North America that are of primary economic importance to plant and animal production systems, stored products and structures, and human health. These species include selected beneficial organisms such as honey bees and predators and parasites of damaging insects.
The rest of the species are generally harmless and properly may be considered beneficial because they are an important component of natural and agricultural ecosystems, functioning as decomposers of plant and animal matter, generalist pollinators, predators, and parasites.
It is estimated that less than 0.04 percent of the known insects are in any way detrimental to humans, but it is this very small number that can disrupt production agriculture in the United States and has led to efforts to document insect plant and insect-animal interaction and to search for insect management strategies.
Sustainable pest management strategies (host plant resistance, biological control, cultural control, and mechanical/physical control) are of particular relevance today because of the interest in avoiding the risk of environmental contamination by unnecessary use of insecticides. Use of multiple and compatible insect management strategies, with particular emphasis on sustainable strategies, is desirable.
Essay # 2. Insect Life Cycles:
All insects begin their development as eggs produced by the adult female. A few species, such as aphids, give birth to live young, but the young are actually hatched from eggs carried inside the mother. After egg hatch, insects grow in a series of distinct stages. Periodically, the insect sheds its exoskeleton (molt) and expands the soft new exoskeleton by inhaling air.
In a few hours the new exoskeleton hardens and there is no further change in body size until the following molt. Through this process the insect is able to expand in size despite being encapsulated in an external skeleton. In some cases, such as many soft bodied larvae, the exoskeleton is soft, allowing limited expansion between molts, but the insect must still molt to complete development.
In many insect species, there are also specialized molting events in which the insect not only sheds its old exoskeleton, but forms a new exoskeleton with new features. All growth ceases following the final molt to the adult stage of the insect. An adult insect will not increase in size as it ages.
The specialized molting process in which the insect undergoes a major change in form is called metamorphosis. The kinds of change vary among different insect groups. Two general types of development predominate- simple metamorphosis (hemimetabolous insects), and complete metamorphosis (holometabolous insects).
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Several of the more primitive orders of insects undergo no distinct metamorphosis (ametabolous insects). The Collembola and Thysanura are examples; developing Insects undergoing simple metamorphosis have three basic life stages- egg, nymph, and adult. The nymphs typically pass through three to five instars, molting between each to attain the larger size of the next instar.
Nymphs and adults often live in the same habitat. The principal changes occurring during metamorphosis are changes in body proportions, sexual maturity, and the development of wings. Examples of insects that undergo simple metamorphosis include grasshoppers and crickets (Orthoptera), earwigs (Dermaptera), cockroaches (Blatteria), “true” bugs (Hemiptera), and aphids and their relatives (Homoptera).
Insects that undergo complete metamorphosis pass through four basic life stages- egg, larva, pupa, and adult. Caterpillars, maggots, and grubs are common examples of larvae. During the larval stage there may be three to seven instars, all of which usually are active and often ferocious feeders. The pupal stage (e.g., cocoon, puparia, chrysalid) is a non-feeding stage that follows the specialized molt from the larval stage.
During the pupal stage, many physiological and morphological changes occur. Internally, the insect is going through the process of changing to the adult form. During the final molt, the adult emerges from the hardened exoskeleton of the pupal case.
Adults are usually winged and may differ from the larvae in a number of ways including type of legs, mouthparts and feeding habits. Adults of insects undergoing complete metamorphosis are very different in form from the larvae. They may be found in habitats similar to the larvae, such as some beetles, or in very different habitats than the larvae, such as bees and butterflies.
Insects with complete metamorphosis include butterflies and moths (Lepidoptera), beetles (Coleoptera), “true” flies (Diptera), and lacewings (Neuroptera). The larval stage tends to specialize in feeding. The adult stage specializes in dispersal and reproduction, but may feed and cause economic damage as well.
Essay # 3. Insect-Plant/Insect-Animal Interactions:
The impact of insect feeding varies from being extremely detrimental to valuable. Plant response can vary from loss of plant tissue or fluids, decay (such as yellowing of leaves), plant structure deformation (such as galling), or no adverse plant response. Inject feeding may also result in increasing the plant’s susceptibility to disease organisms, or in directly transmitting a disease into the plant.
In many cases, insect feeding results in little adverse plant response either because of low plant susceptibility to insect feeding or a low number of insects causing damage.
In some cases insect feeding is actually beneficial to the plant. In the process of gathering nectar and pollen, honey bees and other wild pollinators fertilize flowering plants.
Plant feeders that feed on dead and dying plant tissue are an important part of the carbon cycle, replenishing the soil profile with nutrients. When insects feed on live animals, animal response can vary from loss of animal tissue, blood, skin, hair, or feathers. Allergic and toxic responses can result in further health problems.
Insect feeding may increase the animal’s susceptibility to disease organisms, or transmit an animal disease. As with plants, insect feeding may result in little adverse animal response either because of low animal susceptibility or a low number of insects causing damage. Insects that specialize in feeding on dead animal matter and dung are important recyclers in the environment.
Essay # 4. Insect Collection and Preservation
A properly prepared insect collection is a repository of information that can be consulted and admired well into the future. Properly prepared insect specimens can last for centuries. The value of a preserved insect lies in its beauty and label information, which provides an indication of the biological importance of the specimen.
The equipment used to assemble an insect collection need not be elaborate or expensive. A collecting net and killing bottle is needed to collect insects. To preserve insects, insect pins and storage boxes with soft bottoms to secure hard-bodied insects are needed. Vials and preservation fluid are needed to preserve soft-bodied insects. Insect labels are needed to document where the insect was collected, when it was collected, and who collected it.
When collecting insects, determine if you want your collection to represent the wide diversity of insects or a selected group (such as butterflies, insects found in an alfalfa field, or the Orthoptera of Goshen Country). You should also determine whether you wish to collect adult insects, immature insects, or both.
The tools needed for collecting and preserving insects will be determined by your collection preferences. In addition to a collection net and kill jar, forceps or fine brush for picking up small insects, a knife for opening plants or digging into soil, traps to catch insects, small envelopes, boxes or vials for temporarily storing insects. Bags for storing plant material, a hand lens, and a notebook for taking notes and label data are also useful.
Three types of collecting nets are available. Aerial nets are designed to collect butterflies and other flying insects. Sweep nets are designed to sweep through vegetation. Aquatic nets are designed to screen insects out, of water. Traps can be used to collect insects that are difficult to catch with nets because they are not highly mobile, fly at night, or are found near the ground. Light traps are advantageous because many flying insects are attracted to light. A 15-watt ultraviolet fluorescent light source is often the best attractant for insects.
Flying insects are attracted to the light, hit baffles surrounding the light source, and fall into a collection jar filled with alcohol or a collection bag with plant material placed in the bag (for the insects to rest on until the bag is inspected). Light traps are available through biological supply houses. Pitfall traps collect ground-dwelling insects.
A simple pitfall trap may be made by simply placing bait in a wide- mouthed jar and placing the jar overnight in a location where ground dwelling insects are suspected to occur. Different baits collect different insects; apple cider absorbed onto tissue or a piece of meat placed at the bottom of the jar or suspended in the jar are two commonly used baits.
The trap can be placed among lush vegetation or dug into the ground with the mouth of the jar level with the ground. Vaseline should be spread along the inside rim to make sure that the insects do not escape.
The killing and preservation of insects should be done carefully to ensure preservation of a good specimen. Insects should not be haphazardly killed if they are not to be used in a collection and they are not harmful (the vast majority of insects either do not harm human endeavors or are beneficial).
Killing of soft bodied insects in alcohol or other liquid media should be done with care. Ethanol mixed with water (70 to 80 percent alcohol) is usually a satisfactory killing and preserving agent. Isopropyl alcohol (rubbing alcohol) is an acceptable and commonly available substitute.
Larvae of most insects should be first killed in boiling water to “fix” their proteins, which prevents them from turning black. The “fixed” larvae then can be placed in alcohol for long-term storage and display. Hard-bodied insects can be killed in a kill bottle. This is a preferable killing method for many hard-bodied insects because placement in alcohol may distort the shape of the soft inter segmental regions of the body.
A kill bottle can be made of a wide-mouthed glass jar containing a liquid killing agent. Plaster of Paris can be poured into the jar (about 2.5 cm) and dried. Ethyl acetate (finger nail polish remover) is then poured onto the plaster. The absorbed ethyl acetate will be sufficient to kill most insects (be sure that excess liquid has been poured out of the jar). The time needed to kill an insect will depend upon its size and type and may vary from minutes to hours.
Prior to preservation or pinning, specimens can be temporarily stored. Larval specimens should be prepared for long-term storage in alcohol (usually 70 to 80 percent) as soon as possible. Larvae can temporarily be placed in alcohol before “fixing” the larvae in boiling water.
Do not temporarily store larvae in cool water before they are “fixed”. Hard-bodied insects and most all adult insects can be temporarily stored in the refrigerator or in dry storage prior to pinning. Insects placed in the refrigerator should be in a well-sealed container with moistened tissue paper.
This is a good method of temporary storage because the specimens should not become brittle. Insects placed in dry storage, such as in a plastic or cardboard box sitting at room temperature without moisture, must be rehydrated prior to pinning. To rehydrate, the dried insects should be placed in a well- sealed clean container with moistened tissue paper for one to three days depending upon their size and type.
Soft-bodied insects are commonly preserved in alcohol and stored in glass vials with rubber corks or screw caps. Different-sized vials are available from biological supply houses. As previously mentioned, larvae of most insects should be first killed in slow boiling water for a few minutes to “fix” their proteins, which prevents them from turning black.
The “fixed” larvae then can be placed in 70 to 80 percent alcohol for long-term storage and display. Immatures of orders with simple metamorphosis usually are preserved well when placed directly in 70 to 80 percent alcohol. Parasitic Hymenoptera are best killed and preserved in 95 percent alcohol.
Hard-bodied insects are commonly preserved as pinned specimens. Insects should be pinned directly on the pin or placed on card mounts that are then pinned. Direct pinning can be used if the insect is large enough that the pinning will not break apart the insect.
Standard insect pins are 38 mm long, rust-proof, and a rounded-head end for easy handling. Entomologists commonly use pins of size 2 (0.46 mm. in diameter). No. 3 and 4 size pins are useful for very large insects. Biological supply houses carry insect pins that meet these specifications.
Insects should be pinned vertically through the body. Most insects are pinned to the right of the midline so that all characteristics of one side of the body will definitely be retained. The pinned insect should be level (the long-axis of the body at a 90 degree angle from the length of the pin. The insect should be placed two-thirds or, three- fourths of the way up from the base of the pin to allow placing the locality and determiner labels underneath the insect.
Pinning blocks, which allow adjusting specimens and labels to uniform heights on the pin, are available from biological supply houses or can be home-made. Where the pin is placed along the length of the body depends on the type of insect. Orthoptera should be pinned through the back of the thorax.
Large Hemiptera and large hard-bodied Homoptera should be pinned through the triangular scutellum. Large Hymenoptera and Diptera should be pinned through the thorax between the bases of the forewings. Large Coleoptera should be pinned through the rightwing cover near the base. Large Lepidoptera and Odonata should be pinned through the thorax at its thickest point; the wings should be spread apart uniformly.
Small insects that would break apart if directly pinned should be mounted on card points that can be pinned. Card points are small triangular pieces of stiff paper (stiff paper of 50 percent rag or more), no more than 12 mm long and 3 mm wide. Cutting out the card points with scissors is satisfactory.
For those who collect many small insects that need to be pointed, a special punch to make card points is available from biological supply houses. The card point is pinned through the broad end and the insect is then glued to the point. Clear finger nail polish or white glue is acceptable adhesives to use.
For most insects, the card point is attached to the right side of the insect, with the left and middle sections clear of the card. For better adhesion with some insects, the tip of the card point may be bent down, where the insect will be placed, at a slight angle.
Insects to be preserved with the wings spread uniformly away from the body are dried in this position on spreading boards. A spreading board is a smooth surface on which the wings are spread and positioned horizontally. The body of the insect is placed in a longitudinal groove in the board with the pin secured into a layer of soft material.
Spreading boards can be purchased from biological supply houses or homemade. Wings of Lepidoptera and Odonata should be spread. The pin is inserted in the central groove of the spreading board and pushed down until the base of the wings is flush with the top edge of the spreading board.
The forewing is spread outward by gently pulling it with an insect pin placed behind a large vein at the front edge of the wing. The hind edge of the forewing should be at a 90 degree angle from the length of the body. The hind wing should be spread so that the front edge of the hind wing overlaps the hind edge of the front wing (the front edge of the hind wing should naturally spread underneath the hind edge of the front wing). The positioning of the wings should be secured with strips of paper placed across the wings and pinned to the spreading board.
Drying time will depend upon the size of the insect and humidity; drying time may vary from one to two weeks.
Once the insect is pinned or placed in vials with storage fluid, label(s) should be added to the specimen. Although a preserved insect itself is of value for its beauty, a specimen is of the most value when labeling information is included indicating where and when the specimen was collected; who collected it, and on what host it was found.
Two labels are commonly used for pinned insects (locality and determiner labels). One label with all necessary information is commonly used for insects stored in liquid. The locality label contains the location of collection, date of collection, the name of the collector, and if available the host plant or host animal with which the insect was associated.
The first line should include the state or country where collected followed by more specific township and site information (an additional line can be used if necessary). The state should be capitalized and printed on the upper left hand comer of the label followed by the other information.
The date of collection should be recorded on the next line in day- month-year order. Host plant or host animal affiliation should next be noted if available. The collector’s name should be printed on the next line after or before the letters COL, which signify that this is the collector’s name.
Any other unusual collection circumstances can also be placed on the label (such as burned forest area). The scientific identity of the specimen should be placed on a separate label, called a determiner label (for specimens to be placed in liquid storage, this information should be printed on the locality label).
The first line should indicate the order and family of the specimen (Lepidoptera: Noctuidae). The second and/or third lines should indicate the common and/or scientific names. The last line should indicate the person making the species determination printed after DET: (DET: A. Peters).
A name should not be placed on the last line if a species determination has not been made. Label data for pinned insects should be printed in India ink on paper of at least 50 percent cotton fiber content, using a rapidograph or ultra-fine-pointed crow quill dip pen (pencil can be used, but ballpoint pen should never be used because this ink fades rapidly). Label data for specimens placed in alcohol or other fluid should be printed in soft lead pencil or India ink (the ink should be well dried prior to being placed in alcohol).
Specimens should be stored in containers with tight joints and closely fitting lids to prevent entry of unwanted insects. To prevent fading, pinned insect specimens should not be stored in brightly lit places. The type of box or case depends upon your personal needs and the expected use of the collection. If pinned insects are to be put on display, a glass or clear plastic covered case measuring approximately 16 ½ (depth) by 19 (width) by 3 (height) inches is preferable.