9 Insect Biodiversity

Dr R.K. Chaitanya

1.      Introduction

2.      Arthropod classification

3.      Major insect orders

4.      Insect mouthparts

5.      Insect metamorphosis

6.      Semiochemicals

7.      Social behaviour in insects

8.      Benefits from insects

a.      Ecosystem services: pollination

b.      Insect silks

c.       Bee products and their uses

d.      Scale insects 

e.       Maggot therapy

f.       Ant sutures

g.      Dermestids

h.      Recyclers

i.        Research models

j.        Aesthetics

k.      Biological control

l.        Protein source 

9.      Harmful insects

a.      Insects as pests

b.      Insects of medical and veterinary importance

1.  Introduction

 Insect, (class Insecta or Hexapoda), belong to largest class of the phylum Arthropoda, There are more than 750,000 described species of insects, with new ones being described on a continuing basis. It has been estimated that approximately a billion billion (1018) individual insects were alive at any one time. The adaptability of insects to changing environmental conditions over the millions of years since their appearance on earth is a major contributor to their success. Insects have evolved from a line of ancient annelid-like ancestors that probably also gave rise to the early onychophorans fossils of which are well preserved in Cambrianmarine deposits dating from more than 500 million years ago. Based on the fossil record, the first insects evolved as wingless forms during the Devonian period of the Paleozoic era, about 400 million years ago. The early fossil insects looked much like some thysanurans do today. Great radiation in the evolution of insects occurred in the Carboniferous period (360 million years ago, in the Paleozoic era) when Earth was dominated by large primitive vascular plants and later in this period by ferns and gymnosperms. A second great expansion of insects occurred during the Cretaceous period about 140 million years ago in the Mesozoic period when flowering plants were expanding and gymnosperms were declining. Co-evolving and adapting with flowering plants led to the success and expansion of several groups of insects, including beetles, bees, and plant-feeding Hemiptera. The major reasons of their success are their evolution and adaptation with changing environment. Insects live in many diverse microhabitats, and a small body requires relatively less food to grow and to sustain life. Insects have developed an extraordinary array of sensory receptors that enable them to gather information about their internal and external environments. An exoskeleton provides protection from the external environment, controls water loss from a body that has a very high surface-to-volume ratio, and provides for skeletal muscle attachments. The tracheal system, a system of air-filled tubes, arborizes like the human capillary system to virtually every cell in the body and allows air to move through an air path to within a few micrometers of mitochondria. Consequently, insects nearly always respire aerobically, even during periods of prolonged flight. Thus, they get the maximum energy release from the breakdown of carbohydrates, and some groups can metabolize fatty acids for even greater amounts of energy during flight. Their food habits and alimentary canal structure evolved together, so that diversity in food is reflected in the great diversity in gut structure. The excretory system, based on the principle that most small molecules enter the Malpighian tubules and are passed to the hindgut for selective re-absorption of physiologically useful molecules while those not reabsorbed are excreted with the feces is important in adapting to evolving food plants. Small size has in itself been a major factor in success. They have a very complex endocrine system involving steroid hormones, neuro-secretions, neuro-modulators, biogenic amines, second messengers, and possibly a unique hormone, the juvenile hormone. The use of semiochemicals in communication and location of mates, food plants, and prey is well developed and seems to have reached an apex in moths, which fly at night and depend on olfaction to find food and mates. Sex pheromones play an important role in sexual isolation today and probably have done so for millions of years.

2. Arthropod classification

The phylum Arthropoda can be subdivided into 4 subphylums and further into classes and subclasses based on modification, specialization, number, and appearance of body segments and appendages including mouthparts as described below.

3.  Major insect orders

Order	Typical examples	Key characteristics	Approximate no. of named species
Coleoptera	Beetles	Most diverse animal order; two pairs of wings; front pair of wings is a hard cover that partially protect the transparent rear pair of flying wings; biting and chewing mouthparts; Complete metamorphosis; heavily armored exoskeleton	3,50,000
Diptera	Flies	Front flying wings transparent; hind wings reduced to knobby balancing organs called halteres;. Sucking, piercing, or lapping mouthparts; Complete metamorphosis.	1,20,000
Lepidoptera	Butterflies,Moths	Two pairs of broad, scaly, flying wings, often brightly colored; Hairy body; tubelike, sucking mouthparts; Complete metamorphosis	1,20,000
Hymenoptera	Bees, wasps, Ants	Two pairs of transparent flying wings; mobile head and welldeveloped compound eyes; often possess stingers; chewing and sucking mouthparts. Many social. Complete metamorphosis.	1,00,000
Hemiptera and Homoptera	True bugs, bed bugs, Leaf hoppers, aphids, cicadas	Wingless or with two pairs of wings; piercing, sucking mouthparts, with which some draw blood, some feed on plants. Simple metamorphosis.	60,000
Orthoptera	Grasshoppers, Crickets	Wingless or with two pairs of wings; among the largest insects; biting and chewing mouthparts in adults. Third pair of legs modified for jumping. Simple metamorphosis	20,000
Odonata	Dragonflies	Two pairs of transparent flying wings that cannot fold back; large, long, and slender body; chewing mouthparts. Simple metamorphosis	5000
Isoptera	Termites	Two pairs of wings, but some stages wingless; chewing mouthparts; simple metamorphosis. Social organization: labor divided among several body types. Some are among the few types of animals able to digest wood. Complete metamorphosis.	2000
Siphonaptera	Fleas	Wingless; flattened body with jumping legs; piercing and sucking mouthparts. Small; known for irritating bites. Complete metamorphosis.	1200

4.  Insect mouth parts

Mouth parts typically consist of a labrum, a pair each of mandibles and maxillae, a labium, and a tongue-like hypopharynx. Labrum is loosely referred to as the upper lip. Mandibles are hard, powerful cutting jaws. Maxillae are ‘pincers’ used to steady and manipulate the food. They have a five segmented palp which is sensory and often concerned with taste. Labium is the lower cover, often referred to as the lower lip. It actually represents the fused pair of ancestral second maxillae. They have a three segmented palp which is also sensory. Hypopharynx is a tongue-like structure in the floor of the mouth. The salivary glands discharge saliva through it. The type of mouthparts an insect possesses determines how it feeds.

Fig.1. Insect mouth parts

Fig.2. Insect mouthpart modifications: A. chewing mouthparts of a grasshopper B. the lapping type of a bee C. the siphoning type of a butterfly D. the sucking type of a female mosquito

5. Insect metamorphosis

Many orders of insects (described as Holometabola) undergo complete metamorphosis, with egg, larva, pupa, and adult forms. Others have a gradual metamorphosis (the Hemimetabola and Paurometabola) in which the immature insect, sometimescalled a naiad or nymph, respectively, looks much like the adult without wings (orwith the beginning growth of wings in the later instars).One advantage of the pupal stage in insects exhibiting complete metamorphosis is that it allows the larval and adult forms to have very different food habits and to occupy different habitats, thus reducing intraspecific competition.

Types of metamorphosis

Hormones control and regulate metamorphosis in insects. Three major endocrine organs are involved in development through juvenile instars and eventually emergence of adults. These organs and the hormones they produce are the brain (ecdysiotropin), ecdysial (prothoracic) glands (ecdysone), and corpora allata (juvenile hormone).

6. Semiochemicals

Semiochemicals are chemicals produced and released for communication functions. Semiochemicals produced and released for intraspecific communication are called pheromones. Semiochemicals also functions inter specifically, between species, and these are called allelochemicals. Interspecific semiochemical classification is usually based on the nature of who benefits from the chemical message. Interspecific semiochemicals include allomones benefiting the sender, kairomones benefiting the receiver, and synomones benefiting both sender and receiver.

A pheromone that has an effect upon the physiology or biochemistry of an animal, such as suppression of ovary development in honeybees or stimulation of maturation in the desert locust, is called a primer pheromone because it “primes the pump” by requiring a finite period of time for its action to be effective. In contrast, a sex pheromone that attracts a potential mate is called a releaser pheromone because the pheromone almost instantly releases some behavior, such as upwind searching behavior or attempted mating.

The active species the physical space in which the concentration of a pheromone is high enough to cause a behavioral effect in the receiving individual, and it has been mathematically modelled. Pheromones have been identified from more than 1600 species of insects in 90+ families from 9orders. Pheromones are often described or classified by the behavior elicited from the receiver. There are sex pheromones, aggregation pheromones, alarm pheromones, egg-laying pheromones, brood-tending pheromones, recruitment pheromones, trail-following pheromones, and territory marking pheromones, to name a few.

Pheromone parsimony refers to the fact that the same pheromonal compound, sometimes synergized by additional compounds, can serve multiple functions depending on ecological and behavioural contexts. The phenomenon is prevalent in social insects.

To have sufficient volatility, airborne pheromones have to be relatively small molecules. In general, the molecular weight must not be much over 200, to get the volatility needed. Not all pheromones are airborne; some insect pheromones are contact pheromones and some crustaceans have water borne pheromones. No particular chemical structure is used exclusively by insects as a pheromone, and low molecular weight acids, esters, alcohols, aldehydes, ketones, epoxides, lactones, hydrocarbons, terpenes, and sesquiterpenes are common components in pheromones. A few large molecules serve as pheromones, but they are predominately contact pheromones. For example, (Z)-9-tricosene (a hydrocarbon composed of 23 carbons) is the sex pheromone of the housefly, Muscadomestica

7. Social behaviour in insects

Insects rank very high in the animal kingdom in their organization of social groups, and cooperation within more complex groups depends heavily on chemical and tactile communication. In Hymenoptera (honey bees and ants) and Isoptera (termites), a complex social life is necessary for perpetuation of the species. The society usually demonstrates polymorphism,or caste differentiation. Almost 60,000-70,000 honey bees may live in a single hive. Of these, there are three castes—a single sexually mature female, or queen, a few hundred drones, which are sexually mature males, and thousands of workers, which are sexually inactive genetic females. Workers take care of young, secrete wax with which they build the six-sided cells of the honeycomb, gather nectar from flowers, manufacture honey,collect pollen, and ventilate and guard the hive. One drone, sometimes more, fertilizes the queen during the mating flight, at which time enough spermare stored in her seminal receptacle to last her lifetime.

Castes are determined partly by fertilization and partly by what is fed to the larvae. Drones develop partheno-genetically from unfertilized eggs and queens and workers develop from fertilized eggs. Female larvae that will become queens are fed royal jelly, a secretion from the salivary glands of nurse workers. Royal jelly differs from the “worker jelly” fed to ordinary larvae, but components in it that are essential for queen determination have not yet been identified. Honey and pollen are added to worker diet about the third day of larval life. Pheromones in “queen substance,” which is produced by the queen’s mandibular glands, prevent female workers from maturing sexually. Workers produce royal jelly only when the level of “queen substance” pheromone in the colony drops. This change occurs when the queen becomes too old, dies, or is removed. Then workers start enlarging a larval cell and feeding a larva royal jelly tha tproduces a new queen.

8.  Benefits from insects

a.  Insect pollination

Pollinators provide an essential ecosystem service, namely pollination. Indeed, approximately 80% of all the flowering plant species are pollinated by animals, including vertebrates and mammals (e.g. birds & bats) – but the chief pollinators are insects. Familiar insect pollinators include bees, butterflies, moths, beetles, flies, wasps& ants. Fruit, vegetable or seed production from 87 of the world’s leading food crops depend upon animal pollination, which represents 35 percent of global food production. The total economic value of crop pollination worldwide has been estimated at 153 billion Euros annually. Honey bees, bumble bees, stingless bees, and solitary bees are most widely studied and abundant pollinators. Solitary bees include carpenter bees, leaf-cutter bees, long-horned bees, mason bees, squash bees, cuckoo bees etc. Moths are the most important nocturnal pollinators. Beetles belong to the order Coleoptera, and are the largest set of pollinating animals due to their sheer numbers. They are responsible for pollinating 88% of the 240,000 flowering plants globally. Plants attract flies by producing putrid smells. Typically, no nectar is produced in fly-pollinated flowers.71families of Diptera are regular visitors to at least 555 plant species, which include over 100 cultivated plant species comprising important crops, such as mango, oil seed rape, onion and cocoa. Many fruit-bearing rosaceous flowers in the northern hemisphere are visited and at least partly pollinated by flower flies (Syrphidae). For e.g. apple and pear trees, strawberries, cherries, plums, apricot and peach etc. Figs are keystone species in many tropical ecosystems. Fig wasps are responsible for pollinating almost 1,000 species of figs.

b. Insect Silks

Mulberry silkis produced by the silkworm, Bombyxmori L which solely feeds on the leaves of mulberry plant. These silkworms are completely domesticated and reared indoors. Mulberry silk contributes to around 90% of the world silk production.

Tasar silk is obtained from the Tasar silkworms belonging to the genus Antheraea. There are many varieties such as the Chinese tasar silkworm, Antheraepernyi; the Indian tasar silkworm, Antheraeamylitta and the Japanese tasar silkworm, Antheraeayamamai.

Eri Silk. Eri silk is produced by two species namely Samiaricini and Philosamiaricini. Muga silk. The muga silkworm, Antheraeaassamensis also belong to the same genus as tasar worms, but produce an unusual golden-yellow silk thread which is attractive and strong. This is found only in the state of Assam, India and feed on Perseabombycina and Litsaeamonopetala leaves.

c.  Bee products and their uses

Honey:1 table spoon honey (21gm approx) consists of 64 calories,17.3 gm carbohydrates,0 gm fat and 0gm protein. Honey is made up of glucose, fructose, and minerals such as iron, Calcium, Phosphate, Sodium, Potassiumm & Magnesium. Apitherapy is the medical use of honeybee and bee products such as honey, pollen, propolis, royal jelly and bee venom against disease and disorders. Honey prevents gastroesophageal reflux, shortens the duration of bacterial diarrhoea in infants and young children, help heal burns, minimizes seasonal allergies and cough, prevents high cholesterol, prevents inflammation of ovaries and fallopian tubes and some reports indicate prevention of HIV.

Beeswax: Britain alone imports 1 million pounds of beeswax, which can be used as a base for ointments, polishes, and candle making. Forty percent of all beeswax is used in cosmetic manufacture for lotions, creams, and lipsticks.

Pollen: Pollen is rich in Vitamins (A, B1, B2, B6, C, E), amino acids, and Ca, Fe, K, P, and Na.

Royal jelly: Royal jelly is used to treat anemia, gastrointestinal ulcers, arteriosclerosis, hypo-and hypertension, and inhibition of sexual limitations. Studies indicate its role in cell regeneration & bone marrow production and balance the endocrine system.

Propolis: Bee combines the sap with their own discharges and beeswax to create a sticky, greenish-brown product that is used as a coating or sealing their hives calledpropolis. Propolis is an ingredient in many beauty and skin care products. Topical forms include creams, ointments, and lotions. It can also be taken orally and comes in tablet, liquid extract, and capsule form. Propolis is used in boosting the immune system, healing genital herpes and cold sores, helping the mouth heal after dental surgery, treatment for allergies, as an antioxidant, cancer treatment and prevention, prevent hair fall and stimulate new growth, and in treatment of arthritis, measles and gastric ulcers.

Apipuncture is the therapy by means of bee sting. One of the major peptides in bee venom is Mellitin. Mellitin is used to treat inflammation of rheumatoid arthritis and multiple sclerosis. It blocks the expression of inflammatory genes, thus reducing swelling and pain. It is administered by direct insect sting or intramuscular injections.

d. Scale insects

The scale insects are small insects of the order Hemiptera. There are about 8,000 described species of scale insects. Scale insects are economically valuable for the substances they can yield under proper husbandry.

Lac/Shellac: This is a product from Lac Scale insect, Lacciferlacca, and most of it is produced in India, from where the world receives some 40 million pounds annually. Lac is an important ingredient of many items, including floor polishes, shoe polishes, insulators, various sealants, printing inks, and varnish.

Dyes: Many species of scale insects provide dyes that are used in many products, including cosmetics and for coloring cakes, medicines and beverages. Cochineal is a bright red pigment that is gained from the bodies of a scale insect, Coccus cacti, which lives on cactus plants. Dye obtained from Porphyrophora sp. is used in cosmetic products like eye shadow and lipstick.

e. Maggot therapy

In this therapy live, disinfected fly larvae introduced into non- healing or soft tissue wounds of a human or other animal for the purpose of selectively cleaning out only the necrotic tissue within a wound in order to promote wound healing. The U.S. FDA allowed the production of Phaeniciasericata larvae marketed under the brand name Medical Maggots. In February, 2006, the British National Health Service (NHS) permitted doctors to prescribe maggot therapy.

f. Ant sutures

Species used for sutures are Dorylusgrobodoi and Ecitonburchelli. The larger breeds of ants have soldiers with very large pincers. The ants are held over edges of the wounds. When the pincers are clumped tight, the thorax and abdomen would be pinched off leaving behind the head with the wounds closed at that point. These ants secrete cantharidan, a powerful protein blocker in human body preventing viral infection and reproduction.

g. Dermestids for cleaning skeletons

Carpet beetles are small insects that will feed on almost anything organic, including cereals, carpets, and dried insects in collections. Museum technicians take advantage of this fact, and utilize established colonies of dermestids to clean skeletons of mammals.

h.  Recyclers

There are many, soil- and wood-inhabiting species that shred leaves or tunnel in dead wood. This helps plant materials to decay quickly. Over time, decay creates humus, a type of soil rich in organic matter. There are many insects that are attracted to and feed on carrion including beetles, flies, wasps, and ants. Economic losses avoided every year by the burial of livestock waste by dung beetles only are estimated to be over $3.8 billion.

Blow flies are usually the first to arrive on a dead animal, and they are the first to complete development and depart. Other species follow over time in a relatively predictable sequence as the body decomposes. This change in the species composition of saprophages is called faunal succession. This succession can help forensic entomologists pinpoint the time of death when a body is found.

i.  Research models

Drosphila: 60% of human disease genes have homologues in the fruit fly and hence a good model to study human health, longevity and disease.

Grasshopper: The central nervous system of grasshopper closely resembles to that of humans. So they are used for trials before human for many psyco-active drugs tests. Apismellifera: Model to study longevity; caste distinction and differentiation; social behaviour

Triboleumcastaneum: Model to study embryogenesis and stress responses

Galleria mellonella: Model to study metamorphosis and pathogen infection

Locustamigratoria,  Helicoverpa  and Spodopteraspecies:  Insect  pest  models;  pesticide resistance

Female Anopheles and Aedes mosquito: To study the transmission of disease by insect vectors and to investigate insecticide function and development.

Silkworm: It has conserved immune response and similar pharmacokinetics compared to mammals

Manducasexta: Insect metamorphosis and hormonal regulation

j.Aesthetics

Insects are well known in various areas of arts. Butterflies are certainly one of the most appealing creatures in nature, with colors and patterns that are enjoyed by humans. Colorful butterflies, beetles and spiders are collected by many societies. Native Americans in the United States used parts of insects in a manner similar to feathers in their crafts. Brightly colored wing covers of certain beetles are used for earrings by Jivaro Indians of Ecuador. The Egyptians chose a scarab beetle as a symbol of their sun God. Bees were depicted on ancient Greek coins. Most branches of art have exhibited insects in some form, including a great selection of worldwide postage stamps.

k. Biological control

Some insects are predators of pests such as dragonflies, beetles, bugs, lacewings & wasps. Some are parasites of pests (Hymenoptera and Diptera)

1. Protein source

Being rich source of protein, grasshoppers have been eaten in nearly all regions of the world. They are a common food in parts of Asia and Africa. There are 1,462 recorded species of edible insects. 100 grams of cricket contains: 121 calories, 12.9 grams of protein, 5.5 g of fat, 5.1 g of carbohydrates, 75.8 mg calcium, 185.3 mg of phosphorous, 9.5 mg of iron, 0.36 mg of thiamin, 1.09 mg of riboflavin, and 3.10 mg of niacin.

9.Harmful insects

Insects as pests

Pests of agriculture and forestry: This includes locusts, caterpillars, bugs, hoppers, aphids etc. Locusts are among the most destructive of all insect pests.

Pests   of   stored   grains:    This   includes   Rice   Weevil (Sitophilusoryzae); Lesser  Grain Borer (Rhyzoperthadominica);Rust  Red  Flour  Beetle: (Tribolium spp.);  Sawtooth  Grain

Beetle: (Oryzaephilussurinamensis); Flat  Grain  Beetle: (Cryptolestes spp.);  Indian  Meal

Moth (Plodiainterpunctella); Angoumois Grain Moth (Sitotrogacerealella); Khapra beetle (Trogodermagranarium); Rice moth (Corcyra cephalonica).

Household pests: Common household pests include ants, termites, bed bugs, carpet beetles, furniture beetles, book lice, house flies, fleas, cockroaches, silver fish, clothes moths and spiders.

b. Insects of medical and veterinary importance 

Mosquitoes can spread diseases such as malaria, yellow fever, dengue fever. Tsetse flies spread sleeping sickness. Lice suck human blood and can cause sores. Screw worm flies lay their eggs in the wounds of farm animals and pets. Horseflies and black flies suck blood and have painful bites, which can be infected.