List of twenty-two important insects species found in India:- 1. Silver Fish 2. Springtail 3. Locust 4. Rice Bug 5. Cricket 6. Stick and Leaf Insects 7. Earwig 8. Mayfly 9. Dragon Fly 10. Bed Bug 11. Louse 12. Lac Insect 13. Butterfly 14. Common Windmill (Parities Philoxenus) 15. Krishna Peacock (Papilio Krishna) 16. Kaiser-I-Hind (Teinopalpus Imperialis) and Others.
1. Silver Fish:
These insects, Lepisma saccharina (Fig. 18.94A) are commonly seen in cupboards and book-racks, where they devour starchy products. The body is small, flat and silver- coloured. The mouth parts are adapted for chewing. The compound eyes are insignificant. In the exoskeletal covering, the ventral sternites are not covered by dorsal tergites. The thorax is distinct and the prothorax forms the largest segment of the body.
The abdomen has ten segments. The eighth and ninth segments bear small appendages. The last abdominal segment carries at the posterior end a pair of long, many-jointed cerci and a long tail in between.
The entire body is covered by shining scales. The excrement products are in the form of dry pellets. The heart hangs from the dorsal body wall by means of threads. The adults can moult and possess regenerating power.
These are small, soft and wingless insects (Fig. 18.94B), which live under fallen leaves, decaying vegetation and beneath the piles of logs and woods. The well-known genera are Bourletiella, Isotonia and Nearura. Each antenna is made up of 4-6 segments and the antennae are responsible for perceiving warmth.
These insects prefer moist places and such moist conditions are sought by determining the humidity of both ground and air. The compound eyes are absent but eight identical simple eyes are present on each side. The mouth parts are mostly of chewing type.
The abdomen has six segments and is provided at the terminal end with anal fork or furcula. This furcula remains engaged in the ventral side of the fourth abdominal segment, called hemmule.
When the furcula attempts to extend, it slips out from the catch of the abdominal segment and throws the insect into the air. Luminiscent organs are seen in many and fat body serves as the source of light.
Malpighian tubules are absent and its excretory function is carried by special glands which open above the base of the labium through a common duct. The fat body contains a special kind of cells, called urate cells, which collect uric acid crystals.
The males release hundreds of spermatophores. Each spermatophore remains attached on the surface by a thin hyaline stalk. When these spermatophores get in touch with the moist vulva of the female they burst open to release the sperms.
Some sperms enter within the body through the female genital opening and fertilize the eggs. A pit in the anterior dorsal region of the embryo contains a peculiar filamentous dorsal organ which always absorbs water.
The term locust includes gregarious and migratory grasshopper-like forms. Large head with prominent eyes is curved downwards and incompletely concealed by prothorax. Each lateral side of the first abdominal segment carries a tympanum. In females, the ovipositor is made up of small plates. Some common species of locusts are: Locusta migratoria, Schistocerca gregaria, Pachytylus cinerascens.
The locusts have two phases in their life—solitary and migratory (Fig. 18.94C & D). The migratory phase appears due to some unknown reason and just before migration the population increases rapidly. The swarms move like a cloud and the direction is guided by the flow of wind.
The swarms of locusts damage plant population severely in course of their journey. The swarming does not occur each year. The wingless young locusts also migrate by hopping. Usually they moult five times. At the end of fourth moult the instar is sexually active but the fertility is reached only after the fifth moult.
4. Rice Bug:
The rice bug (Leptocorisa varicornis), commonly known as Gundhi bug, is a Hemipteran insect causing serious damage to paddy crop. It has a typical hemipteran body plan with sucking type of mouth parts.
This insect emits an unpleasant odour from the abdominal scent gland, so the name Gandhi bug for the insect. The milk stage of the paddy grain is its main target. The rice bug sucks out the milky juice and leaves only the white chaffy husks. In case of severe infection all the paddy grains become chaffy.
The pests breed amidst wild grasses in uncultivated areas near paddy fields. When the rice is advancing in milk-grain stage, the adult insects invest the cultivated areas. An adult insect has a slender body with a length of about 15 mm.
The anterior pair of the wings is tough and thick while the posterior pair is membranous in nature. The insect is greenish in young stage which turns into a mixture of green and brown in adult which finally turns into brown in old stage.
Females lay small blackish-brown beadlike eggs. The rounded eggs remain arranged in linear fashion on the ventral surface near the midrib of leaf blades of the host plants. The eggs require about a week’s time to hatch. The resultant nymphs, immediately after emergence, start sucking the plant juice and develop into adults within two to three weeks’ time.
Routine-wise schedule as preventive measures:
(i) Selection of paddy-growing areas free from wild grasses which are the host plants on which the rice bug inhabits.
(ii) To clear off paddy stubbles by ploughing or by burning and scrapping of bunds as a regular routine.
(iii) Step up of light traps can be used in field with contact insecticide near paddy field to attract adult pest during milky stage of paddy grain.
(iv) Regular check-up of egg masses on paddy field and immediate step is advisable if egg masses are noticed.
(i) Contact insecticide—5% BHC spray or dust on crops and bunds.
(ii) Paddy field is to be flooded with water and then insecticide along with oil emulsion is to be applied. Nicotine sulphate, lubricating oil emulsion, kerosine emulsion or lime sulphur solution are generally used.
These solitary insects (Acheta, Gryllus) live in warm places. The paired antennae are long (Fig. 18.94E). The elongated ovipositor is spear-shaped. The sound producing stridulating apparatus consists of a scraper in the base of one wing and a file on the base of other wing.
As the wings vibrate rapidly the file rubs over the scraper to produce the characteristic chirping sound. A kind of cricket, called the mole cricket, Gryllotalpa (Fig. 18.91F) has stout and clawed prothoracic legs for the purpose of digging.
6. Stick and Leaf Insects:
These insects have perfectly copied the structures of branches and leaves of the trees (Fig. 18.94G & H). Such mimicry protects them from enemies. The females exhibit more accurate mimicry than males. In general these large-sized herbivorous insects are provided with distinct eyes and multi-jointed antennae. The stick insects (Diapheromera, Carusius) may be 30 cm in length.
The mesothorax is the largest segment. The legs and other parts of the body assume branch-like appearance. Similarly in leaf insect (Phyllium), the wings and other parts of the body extend to be leaf-like. The eggs resemble the appearance of seeds and newly hatched young’s also exhibit mimicing features. It gradually increases in size with each moulting.
These insects (Forficula auricularia) (Fig. 18.94 I & J) are usually nocturnal and carnivorous. The terminal part of the abdominal appendages is forceps-like. The mouth parts are built for chewing. The fore-wings are small and the hind-wings are large. The females brood over the eggs.
The mayflies, Ephemera (Fig. 18.95A), are noted for two unique features:
(i) Winged adult stage has a life span of one day and
(ii) Moulting occurs in a winged form.
The adult aerial form has two pairs of unequal membranous and triangular wings. The abdomen ends in long cerci which may or may not have median terminal filaments. The adult dances in air and lay eggs in water.
The development continues almost for a year and involves twenty-three moultings before the emergence of adult state. The aquatic larvae are free-swimming and possess rows of tracheal gills on each side of the abdomen for respiration. Finally, they break the nymph wall and come on land to rest in some places like trees or walls. Another moulting of this winged form liberates the full-grown adult.
9. Dragon Fly:
These are usually large-sized insects. The common genera are Macromia, Aeschea, etc. It is provided with chewing mouth parts and membranous wings. Sometimes the hind- wings are larger than the fore-wings. At the time of rest, the wings are held horizontally (Fig. 18.95B). The compound eyes are quite prominent but the antennae are short. The abdomen is elongated, slender and threadlike.
The dragon flies are predators and hunt other insects like a kite. The mating takes place during flight and the eggs are released in water. The larvae, called nymphs, are aquatic and respire through a special kind of aquatic gills. The elongated labium is provided with hooks and remains folded during rest. It is extended rapidly during food capture.
10. Bed Bug:
These sanguivorous ectoparasites live in close association with man and are cosmopolitan in distribution. Number of diseases, i.e., anthrax, leprosy paratyphoid, oriental sore is believed to be caused by bed bug (Cimex lectularius, Cirotundatus).
The beddings, furniture and crevices of the room are the favourite abode of these insects. The warmth as well as the smell of the host attracts them and the bed bugs are active specially during night.
The adults (Fig. 18.95C) are 4-5 man in length and 3 mm in breadth and are reddish brown in colour. Flat and oval body is profusely covered with bristles and hairs, short head distinct paired compound eyes and a pair of four-jointed antennae. The mouth parts are adapted for piercing and sucking. For that purpose, the mouth parts have formed a proboscis which encloses needle-like maxillae and mandibles.
When not in use the proboscis is kept folded on the ventral side of the body. The prothorax is semilunar and the mesothorax is triangular. The pointed end of the mesothorax is directed backwards and it bears atrophied first pair of wings. There is no trace of second pair of wings. The abdomen is flat and contains eight distinct segments.
In males, the abdomen is more pointed. A curved penis is lodged in a deep groove in the left side of the eighth abdominal segment. The stomach serves as a crop and stores blood during meal. This blood may be retained for several weeks. The saliva, which mixes with the blood meal, contains anti-coagulating enzymes which keep the blood liquid.
The digestion takes place in the intestine. The first part of the midgut is formed by vacuolated cells and is concerned with the absorption of fluid from the meal. Only a little haematin material passes within the hindgut. The blood cells or haemocytes of bed bug do not enter within the cavity of the heart.
The haemocytes remove debris from haemolymph at the time of moulting. It can live for weeks without food and water. Lack of water leads to the formation of dry yellow urine. The inner surface of sternum in mesothorax carries paired stink glands, which produce characteristic smell of the bed bug. The secretions of these glands are transparent, oily, volatile and strongly acidic.
The secretions are released through a pair of median apertures. The stink glands of nymph stage are abdominal in position and three in number. In the adult stage, these glands atrophy and new thoracic glands appear. The genital segment of male, at the posterior end of the abdomen, is provided with a pointed clasper (Fig. 18.95D).
During copulation, the sperm cells are deposited in a pouch on the lower surface of the female abdomen. These cells reach the genital tract after travelling through the general body cavity. Most of the eggs are fertilized, when still in the ovary. The eggs when laid are glued to the substratum by a mucilagenous coating.
The young hatches out by lifting a lid on the egg, called operculum. The metamorphosis is incomplete and the young is called nymph. Such nymphs are yellowish white and 1.5 mm in length. The growth and conversion to adult structure involve five moults. Nymphs are also able to suck blood and it is believed that the distension of the abdomen of nymph due to blood meal causes moulting.
Three kinds of lice are seen—Book-lice (Fig. 18.96A), Biting lice (Fig. 18.96D) and Sucking lice (Figs. 18.96B & C).
The book-lice include numerous kinds of species. These are minute, insignificant and soft-bodied insects having peculiarly modified biting mouth parts. Though they are called book-lice, majority of them live on trees and only a few live within old papers. Two pairs of wings are membranous and have characteristic pattern of venation. At the time of rest the wings are held roof-like over the abdomen.
The biting lice include more than 2500 species, all of which live as ectoparasites on birds and mammals. The body is flat and covered with bristles. The wings and compound eyes are absent.
The mouth parts are adapted for biting but much reduced. Food usually includes the feathers or hairs of the hosts but some are blood-suckers. Eggs are glued with the feathers or hairs of the host and the larvae are also ectoparasites. Development involves three moultings.
The sucking lice are exclusively ectoparasitic. All are blood-suckers and for that purpose the mouth parts include thin stylets within a cephalic sac. The wings and eyes are absent. All the thoracic legs have well-developed claws. The human head and body louse is known as Pediculus humanus.
12. Lac Insect:
The lac insects are scientifically known as Tachardia lacca. Previously, the genus Tachardia was known as Kerria. Two species under the genus are very common—K. lacca and K. chinenses. Of the species, Kerria (Tachardia) lacca is the common Indian variety. India is the highest lac-producing country.
Thailand comes next to India regarding lac production. These insects live on certain specific trees like kusum, khair and ber (kul). It liberates a resinous product as exudate which forms a crust around the insect. From this exudate a product, called lac, is obtained.
Thus, lac is regarded as resinous secretions produced by the female members of the lac insect. In order to obtain lac, these insects are cultured and the technique of lac production is called lac culture. It involves proper care of host plants, regular p running of the host plants, propagation of insects and collection and processing of lac.
For the purpose of propagation the older branches (approximately 23-30 cm) containing crusts are tied with new branches and this method is called inoculation. When new crusts are formed, most are collected and this collection is known as harvesting.
According to its harvesting season, the lacs are classified into two types:
(1) Kusmi lac:
It grows on kusum trees and is inoculated in January-February and harvested in June and July of the following year.
(2) Ranjeeni lac:
It grows on other trees excepting kusum. The inoculation time is October-November and harvesting time is May-June. The kusum trees being much larger in size, provides more surface area and thus the yield of Kusmi lac is higher than the Ranjeeni lac.
After inoculation, lac insects come out of the old crusts. At this stage they are known as nymphs, which have hatched out from the eggs, laid by the females in the old crusts.
When nymphs vacate the old crust, the crust is called Phunki. The phunki must be removed within three weeks from the date of inoculation; otherwise it will be susceptible to parasitic infection. The coming out of nymphs from older crust is called swarming.
These nymphs are boat-shaped and reddish in colour. Each nymph possesses three pairs of thoracic legs, one pair of antennae and a pair of caudal setae. Some of the nymphs become winged or wingless male and others become female (Fig. 18.97). These nymphs explore new branches. It sucks cell sap by piercing the branches with the help of specialised maxillae and mandibles.
The nymph settles in a suitable spot and liberates a kind of exudate. The nymphs gradually lose most of its body structures and undergo repeated moulting. The thrown-out skin together with the exudate forms a crust around it. Each crust contains a pair of branchial pores for respiration and a big anal tubercular opening. In male, the tubercular opening is provided with an operculum.
After three moultings the males come out by removing the operculum and copulate with the female. The males are devoid of mouth parts, for this reason they die soon after copulation.
Most of these crusts are removed at the time of harvesting and are used for extracting lac. As the males are short-lived, they produce lesser lac than the female. The production of lac is good, if the ratio of male and female remains 30: 70. If number of male increase in a particular year, the crop is said to be poor.
Extraction of lac:
The mature incrusted twig is cut. Then the incrustations are washed thoroughly and scraped to remove the secreted materials. These materials constitute the granular lac which is dried and bleached in the sun. The granules are taken in suitable pot and heated by open charcoal fire.
During heating the lac is forced out as it melts. Pigments can be used as dyes at this stage. In molten condition, these materials are stretched into sheets. After drying, these sheets are broken into flakes.
Uses of lac:
Lac has great commercial value. It is extensively used in the manufacture of:
(i) Lithographic ink,
(ii) Varnishes and polishes,
(iii) Sealing wax,
(iv) Electrical insulating material,
(v) Shoe polishes toys ornaments, etc.
For their colourful texture and elegant movement, these daytime flying insects are regarded as the symbol of grace, beauty and austerity. The head bears two large compound eyes, each with numerous ommatidia.
A pair of club-shaped antennae characterise the butterfly. The butterflies have two pairs of large wings which at the time of rest are held high over the body, like sails of a boat. The equal-sized wings are provided with hairs and scales.
The sucking type mouth parts are formed by a long-coiled proboscis. It is formed by the union of two halves of a tube; each half represents the outer part of maxilla. The proboscis remains coiled; when not in use, under the head and extends during use. The mandibles are insignificant. Labium is absent but the labial palp is well extended. Each type of butterfly has preference for a particular plant to lay eggs.
The larva after hatching out of egg often eats voraciously. The larvae, which are called the caterpillars (Fig. 18.98), have powerful mandibles, three pairs of jointed thoracic legs and four to five pairs of un-jointed abdominal legs. The growth of caterpillar involves the shedding of old cuticle. Within a fortnight the caterpillar sheds its skin repeatedly and becomes full-grown.
After certain period of growth the caterpillar produces around its body a covering and becomes sedentaric pupa. The secretion is produced by special silk glands which are present in the body of caterpillar. The pupa is also known as chrysalis and it possesses a slender stalk. Rapid transformation of body parts occur within pupa.
Various caterpillar structures are then replaced by the appearance of adult parts. On completion of the development, the butterfly emerges by breaking the pupal case. Immediately after coming out, the body remains soft. Following butterflies are well-known in our country.
14. Common Windmill (Parities Philoxenus):
These beautiful velvety black coloured butterflies (Fig. 18.99A) are found in the Himalayan region specially in Assam. The size is 11 to 15 cm across. The anterior wings are smooth in outline but posterior wings are peculiarly notched. The posterior wings are also marked by beautiful red spots.
15. Krishna Peacock (Papilio Krishna):
These large butterflies (Fig. 18.99B) with wingspan of 10 cm have beautiful green texture with red, yellow and blue markings. They are quite common in the Himalayan region, specially in Sikim and Bhutan. The posterior wings are peculiarly lobed.
16. Kaiser-I-Hind (Teinopalpus Imperialis):
These rare butterflies (Fig. 18.99C) of Assam, Nepal and Sikim exhibit sexual dimorphism. Males have a single tail but females have three. They generally live on the top of the tree and on rare occasions come to the ground.
17. Rice Butterfly (Melanitis Ismene):
These deep brown coloured, shade-loving butterflies (Fig. 18.99D) are quite common in India. They lay eggs on paddy plants and have characteristic coloured eye spots at the centre of the wings. The caterpillars are green.
18. Cabbage Butterfly (Pieris Brassicae):
These white, yellow or organge-coloured butterflies (Fig. 18.99E) are often seen in agricultural fields. They lay eggs on cabbage and other plants under Cruciferae, and pupa remains in upright position. These are migratory in nature.
These are insects with hard integument and chewing mouth parts. The prothorax is large and movable. The stiff and hard anterior wings, known as elytra, cover the posterior wings completely. Some are wingless. It exhibits complete metamorphosis and larvae are provided with well-developed head, biting mouth parts and three pairs of legs.
Following beetles are very interesting:
These oval bodied beetles (Fig. 18.100A) are provided with short antennae and small legs. It lives upon leaves of various plants like potato, cucumber, etc.
Eleven segmented antennae of these beetles (Fig. 18.100B) are longer than the body. Larvae are wood-borers.
These small, more or less round beetles (Fig. 18.100C) are noted for their habit of feigning death. These beetles are commonly seen in the fur of museum specimens, carpets, woolen dresses and in different other domestic goods. Its abdomen remains fully enclosed by the elytra. The well-known examples are Anthrenus, Dermestes.
Lady Bird Beetles:
These beneficial insects (Fig. 18.100D) destroy aphids and other plant pests. They have beautiful red-coloured bodies with black spots on it. They are distributed throughout the world.
These large aquatic beetles are seen throughout the world in fresh-water ponds, lakes and pools. Their food includes small fishes, aquatic insects and other small aquatic organisms. The adults have thread-like antennae, oar-shaped hind legs, and they can fly well.
While diving inside water they carry a film of air beneath their wings. The large-sized whirligig beetle (Fig. 18.100E) at the time of diving carries a bubble of air at the posterior end of the body. The larvae possess strong mandibles and long abdomen.
These beetles (see Fig. 8.10B) are well known for their ability to emit light. For this purpose, they possess phosphorescent organs which are present in the posterio-ventral aspect of the abdominal segments and are in connection -With traches. A substance luciferin is present in this organ, which is oxidised in the presence of an enzyme luciferase to produce light in them which is without heat.
These beetles have peculiar elongated head which is drawn to form a rostrum. These are highly injurious to plants, fruits, seeds and stored grains. The well-known examples are—rice weevil (Calandra oryzae), mango weevil (Apion sp.).
They are also known as scrab beetle and were considered sacred in ancient Egypt. They are well-known for their parental care. They prepare small spheres by rolling dung, and eggs are laid on them by the females. These balls are deposited in a hole. When the grub comes out it uses the dung as food.
Two kinds of wasps are well- known—Spider wasps and Hornets. The spider wasps are large, active, long-legged and hunt spiders. These wasps build underground burrows and place a paralysed spider within it. One egg is laid on each spider. When the larva hatches out, it eats the spider.
The hornets live on nectar, ripe fruit, sugary fluid and also eat larvae and small insects. Some are solitary but many exhibit highly organised social life. A family includes queen, males and workers.
After copulation, the queen hibernates for a year and then starts to lay eggs. First lot of eggs develops into workers, and then queens and males emerge. Its nest is papery and has several tiers and the entire nest is enclosed within an outer envelope.
Ants are well-known example of the insects which exhibit polymorphism. Like termites and bees, they also lead a social life.
There exist innumerable types of ants (nearly 3,500 species) which abode various places from burrows to specially formed nests. In ants the abdomen is distinctly separated from thorax, and antenna is divided into an un-jointed basal part and a many-jointed upper part.
Colony of ants includes following forms:
1. Queens or cynes
2. Kings or Anes
3. Workers or Ergates and
4. Soldiers or Dinergates.
Only the males and the females possess transparent wings and enter into nuptial flight. At the end, they lose their wings and the female lays eggs. From each egg an elongated legless grub is developed which transforms into pupa. These pupae develop into workers (Ergates) which start to take care of the nest. As in bee the unfertilized eggs produce males, and fertilized eggs give rise to workers and females.
The workers are wingless and possess female gonads in arrested state of development. Some workers undergo special modification in their structures to act as soldiers. The workers do all sorts of work and the males and the females are dependent on them.
The job of the workers includes collection of food, protection of the nest, rearing of grubs and pupa, cleaning of the nest. It has now been determined that a substance, called pheromone, guides the foraging workers to identify the way to its own nest.
Some ants are known to rear insects like beetles, aphids in their nests. Specially these aphids when touched by the antennae of ant secrete a juice and for this reason they are known as ant-cow. The soldiers are modified workers which are devoid of wings but possess large heads and powerful mandibles. Their role is to protect the colony from the enemies.
The well-known ants (Figs. 18.101B & C) are common red ant (Oecophyla smaragdyna), black ant (Componotus compressus), European wood ant (Formica rufa), etc. Ants often destroy vegetations but at the same time they are effective pollinating agents. Several ants kill caterpillars, bugs and beetles and thus serve as important agent for biological control.
These insects in their adult stage live as ectoparasites on birds and mammals. Nearly 1500 species are known. The body is laterally compressed, brown and strongly sclerotised (Fig. 18.101D). The head is small and the mouth parts are adapted for piercing and sucking. All are sanguinivorous. The wings are absent, but the legs are well developed and specially the hind legs are adapted for leaping.
A female flea lays nearly 300-500 eggs. The larvae are white, small and wormlike. The head of the larva carries a spine, which breaks open the egg shell at the time of hatching. The larva is free-living. The next stage pupa covers itself with a silken cocoon, impregnated with sand grains and debrises.
The most notable flea is rat flea (Xenopsylla cheopis) which carries a bacterium (Pastaurella pestis) from infected rats and causes Bubonic plague in man. The same flea also infects another disease, called endemic typhus. The other important fleas are Pulex irritans (human flea), Ctenocephalides felis (cat flea) and Ctenocephalides canis (dog flea).