Total Lectures: 45.
1.1 Definition & scope.
1.2 Types of diversities among insects.
2. Insect & it’s environment: (4)
2.1 Insect diversity & adaptations with reference to terrestrial habitats: forest, agriculture, subterranean, cave, glacier, mountain & desert.
2.2 Insect diversity & adaptations with reference to aquatic habitats : river, stream, lake, pond, torrents, marine, estuarine & ephemeral water bodies.
3. Population dynamics of Insects: (3)
3.1 Concept of population dynamics.
3.2 Factors affecting population dynamics in insects.
3.3 Seasonal variations in insect populations.
4. Insect taxonomy: (9)
4.1 Outline of scheme of classification of insects as given by Richards & Davis.
4.2 Distinguishing features of Apterygotan insects.
4.3 Distinguishing features of Pterygotan insects : Exopterygota & Endopterygota.
4.4 Distinguishing taxonomic features & significance of following major insect orders:
Orthoptera, Diptera, Hemiptera, Lepidoptera & Coleoptera.
4.5 Useful contribution in molecular phylogenetic studies.
5. Insects in social groups: (5)
5.1 Definition, intraspecific & interspecific relationships among insects.
5.2 Social organizations in ants, wasps & termites.
5.3 Significance of social organizations.
6. Food & feeding behavior in insects: (4)
6.1 Selection of food by insects.
6.2 Food diversity among insects.
6.3 Significance of diversity in food & feeding habits.
7. Breeding behavior in insects: (6)
7.1 Diversity in courtship & oviposition behavior in insects.
7.2 Diversity in oviposition sites among insects.
7.3 Parental care & nest building diversity in insects.
7.4 Diapause behavior in insects.
8. Diversity in insect relationships: (5)
8.1 Diversity in mutualistic associations: ant-aphids, ant-coccids, ant-bug, ant-butterfly &
8.2 Insects as predators, parasites & parasitoids.
8.3 Insect plant interaction: Role of insects as plant bodygaurds.
9. Survival strategies in insects: (3)
Escape, flight, sting, poison, mimicry, hide, camouflage & migration.
10. Effect of changing climate & human interference on insect diversity: (4)
10.1 Impact of global changes on diversity of insects at various levels such as local, regional, national & global.
10.2 Important steps essential for conversation & management of insect diversity.
1.Imm’s General Text book of Entomology Vol. I & 11(1993), Richards O.W. &Davis R.F.., B.I. Pul (Indian edition) New Delhi.
2. Principals of insect morphology, Snodgrass R.E. (1994) Indian Reprint, SBS Pub. New Delhi.
3. Structure & functions of Insects. Chapman R.F. (1983), edition, ELBS, London.
4. Entomology, Gillott Cedric (1980), Plenum Press, New York.
5.The Science of Entomology, Romoser W.S. (1981) 2’’ edition, Mac millon Co., New York.
6. General Entomology, Mani M.S. (1998) Reprint Oxford- IBH, India.
7 An Introduction to Entomology, Srivastav R.D. & Singh R.P. (1997), Concept Pub. New Delhi.
8.General & Applied Entomology, Nayar K.K., T.N. anantkrishanan & B.V. David, (1983), tata McGrow Hill, Pub. New Delhi.
9. Insects, Mani M.S. (2006) Reprint NBT Pub. New Delhi.
A specialized segment of the population of social insects, castes have different functions within the society and sometimes different morphologies. Castes have distinct divisions of labor
Social systems characterized by parental care of young, overlap of generations, and reproductive division of labor. True sociality.
The maintenance of a functional steady state in an organism or superorganism
Behavioral differences among castes
Caste members are radically different in appearance, us. results from environmental (food) differences
Insects that live cooperatively in colonies and exhibit a division of labor among distinct castes. ex. termites, ants, bees, some wasps.
A social insect colony described as a multicellular animal, individual members of the colony are similar to individual cells in an animal
Traits of Eusocial Insects
- Reproductive Castes - queen and drone
- Queen - produces eggs to maintain the colony.
- Drones - mate with new queens.
- Worker Caste - sisters, all daughters of the queen
- Care for the eggs, larvae, queen and drones.
- Maintain and defend the hive, and forage for food.
SocialityMost insects are not social, some aggregate or contact other members of their species for short periods to mate or for other functions. Some even dispense with mating and reproduce asexually.
Only a few groups are truly social.
All termites (Isoptera), some Hymenoptera (all ants, honey bees, stingless bees, bumble bees, and some members of other bee groups, and at least one wasp sp.).
True social insects, esp. the ants and termites, are dominant ecological groups.
ADVANTAGES & DISADVANTAGES OF SOCIALITY
Hide from predators
Colony productivity increased
No competition with others of your species
Group defense and alarm
Live in small spaces
Exploit small food resources
Care of young
Lack of social benefits
Intense predation, parasitism, disease
- Reproductives - queen and drones
- May be distinct morphological types, esp. in ants.
- Lacking in wasps and bees.
Three Castes of Termites
A Winged Adult Reproductive Termite
A Wingless Termite Worker
A Wingless Termite Soldier
Comparison of Isoptera and Hymenoptera Caste Systems
Workers and Soldiers
Male Reproductives (Drones, Kings)
Immature or adult
Permanent attendant of the queen
Die after mating
Unlike bees, in termites the male is not a drone. Workers may be males and the king has functions other than mating. The queen may live for more than 10 years. But if she is killed or her egg production declines, secondary queens replace her.
Caste members may be radically different in appearance from one another or polymorphic and castes may have subcastes that differ in appearance and function. This usually results from environmental (food) differences not genetic differences. Behavioral differences among castes are called polyethism.
WHO RULES THE HIVE?The Queen Bee
- Lays all the eggs and regulates sex of offspring (parthenogenesis).
- Unfertilized eggs -> males
- Fertilized eggs -> females
- All members of the hive are the queen's progeny.
- The queen's pheromones identify hive members.
- Workers determine type of egg laid by queen.
- Large cells receive unfertilized eggs that develop into males -- males haploid.
- Smaller cells receive fertilized eggs that develop into females -- females diploid.
- Workers determine whether a female egg develops into a reproductive or worker.
- Workers receive royal jelly only their first three days.
- Queens receive royal jelly throughout the larval stage.
DOES TRUE SOCIALITY EXIST IN MAMMALS?
- Wolves, killer whales, lions, man
- SW African naked mole rats
SUPERORGANISMSSteps in evolution of animal size and complexity
- Single celled animals
- Colonial animals
- Clusters of cells capable of independent life
- Multicellular animals
- Groups of interdependent cells
- Cellular division of labor
- Cells not capable of independent life
- Cellular communication and coordination essential
- Most cells no longer reproducing new individuals
- Groups of interdependent, individual insects
- Individual division of labor - castes
- Individuals not capable of independent life
- Colony individual to individual communication essential
- Most individuals are not reproductive.
Peculiarities of Insect Societies
SLAVERYA biological, not a cultural trait, that is wide-spread among ants. Most ant battles you see are actually slave raids. Ant slavery is unique because ant slavery is usually between species, unlike human slavery.
Slave making ants
- Capture larvae and pupae of another species.
- Carry them back to there own nest where:
- They acquire the nest odor.
- Develop into adults and act as workers for their new colony.
WARFAREEmbodies restless aggression, territorial conquest, and genocidal annihilation of neighboring colonies. Ants war with their own and other species and use a variety of tactics.
Imported Fire Ant, Solenopsis invicta vs. the Woodland Ant, Pheidole dentata
The fire ants have colonies hundred times larger than the woodland ant and whenever they discover a woodland ant colony they completely destroy it. Yet woodland ant colonies are abundant around fire ants. Whenever, a woodland worker discovers a fire ant scout soldiers are so rapidly deployed that the scout rarely makes it back to its colony. The soldiers do not sting or spray poisons like many ants but rely on large mandibles to cut their opponents into pieces. If despite this the woodland nest is discovered the soldiers fall back to form a short perimeter around the nest which keeps the invading fire ants at bay temporarily. The colony evacuates the nest and after the battle and the fire ants have departed, they will return and reclaim their nest.
FARMINGMany ants keep insect livestock in the order Homoptera. Commonly seen in our area are ants tending aphids. The ants herd the aphids and protect them from predators and parasites, in turn, the aphids reward the ants by providing with droplets of sweet and nourishing honeydew. Besides aphids, scale insects, other Homoptera, are farmed and some insects in other orders.
Other ants and some termites are gardeners. They collect plant material, bring it into their nests, compost it, and use it to grow fungus which they feed on. Leaf cutter and parasol ants are examples.
AIR CONDITIONINGSome social insects are able to maintain steady state conditions in their colonies or nests, e.g. in temperature and humidity. This is called homeostasis and is essential for colony health.
Examples: Honey bees
- Ventilate their hives - if too hot, wax melts.
- Cluster to stay warm in the winter - if too cold, individuals die.
- Soft bodied, very susceptible to desiccation.
- "Air conditioned" termite mounds - vent heat and retain humidity.
~ Disappearing Act
Habitat: deserts Size: 2.5cm long Adaptation: can dig a hole in the sand using its stout, spiny legs & disappear into it within a few seconds; drink moisture that condenses on plants early in the morning Diet: aphids Predator(s):
Habitat: deserts Size: less than 6mm Adaptation: lay its eggs in the stalk, seed or fruit of plants & the young grubs eat their way out Diet: Predator(s):
Habitat: deserts Size: 2-35mm Adaptation: stands with some of its feet lifted off the hot ground; can emit a foul-smelling black fluid, driving away its adversaries Diet: dry, decomposing plant or animal tissue Predator(s): birds, reptiles & amphibians
~ Spiky Jaws
Habitat: deserts Size: ≈ 1cm long Adaptation: digs funnel-shaped pits near cacti to trap ants & insects Diet: ants & insects Predator(s): Extra: Adult ant lions look like dragonflies
Habitat: deserts Size: 0.8-4cm from tip to tip of its spread wings Adaptation: breed quickly Diet: nectar of flowers & other plant liquids Predator(s): birds; flies & wasps lay their eggs on or in the bodies of the butterfly caterpillars
~ Paralyzing Sting
Habitat: deserts Size: Adaptation: has a sting to paralyse other insects Diet: larva feeds on flesh of paralysed insects; adult feeds on nectar Predator(s):
Desert grasshoppers such as the sand grasshopper can only feed and reproduce following rains that lead to the germination of green plants.
The rest of the time, and during the heat of the day, the sand grasshopper must shelter. Some desert grasshoppers shelter on trees and shrubs, but the sand grasshopper covers itself with sand. The sand grasshopper has special long middle legs to scoop out sand and eyes located at the very top of its head so it can sit buried with just its eyes and antennae exposed.
Desert grasshoppers do not breed regularly. Whenever it rains they feed, reproduce and lay eggs in the soil. Eggs can remain dormant for years if necessary, until the next heavy rain.
Ants and Aphids associationAnts and aphids share a well-documented relationship of mutualism. Ants feed on the sugary honeydew left behind by aphids. In exchange, the ants protect the aphids from predators and parasites. In fact, honey ants will go to unusual lengths to ensure the health of the aphids in their care.
Aphids suck the sugar-rich fluids from their host plants. Because these liquids are low in nitrogen, the aphids must consume large quantities of them to gain adequate nutrition. The aphids then excrete equally large quantities of waste, called honeydew, which is high in sugar content.
Where there's sugar, there's bound to be ants. Some ants are so hungry for the honeydew, they'll actually "milk" the aphids to make them excrete it. The ants use their antennae to stroke the aphids, stimulating them to release the honeydew. Some aphid species have lost the ability to poop on their own, and now depend on their caretaker ants to milk them.
Aphid-herding ants make sure their "cattle" stay well-fed and safe. When the host plant is depleted of nutrients, the ants carry their aphids to a new food source. If predatory insects or parasites attempt to harm their wards, the ants will defend them aggressively. Some honey ants even go so far as to destroy the eggs of known aphid predators like lady beetles.
Some species of honey ants continue to care for their aphids during winter. The ants carry the aphid eggs home, and tuck them away in their nests for the winter months. They store the precious aphids where temperatures and humidity are optimal, and move them as needed when conditions in the nest change. In spring, when the aphids hatch, the ants carry them to a host plant to feed.
While it appears the ants are generous caretakers of their aphid charges, they've really got their own interests in mind. Aphids are almost always wingless, but certain environmental conditions will trigger them to develop wings. If the aphid population becomes too dense, or food sources decline, the winged aphids can fly to a new location. Not wanting to lose their food source, honey ants may prevent aphids from dispersing.
Ants have been observed tearing the wings from aphids before they can become airborne. A recent study has also shown that ants can use semiochemicals to stop the aphids from developing wings, and to impede their ability to walk away.
Study of soil, aquatic, scavenging, arborial & cave dwelling insects with respect to their body part adaptations & ecological significance.Ecological significance.
Terrestrial Insects. The vast majority of insect species are adapted to a terrestrial life style. A rigid exoskeleton is often accompanied by a body surface that is resistant to water loss. The evolution of wings and the elaborate development of legs has afforded numerous options for locomotion on land.
Aquatic Insects. Although only about 5% of the insect species are aquatic, those that are represent an array of taxonomic groups. Aquatic insects may be predators, herbivores, or scavengers. Adaptations of aquatic insects are also varied, enhancing the likelihood of survival in various aquatic habitats. Various structures, such as suckers, claws and hooks, have been modified from legs and body parts to allow insects to cling to an underwater substrate in moving streams. Insects that inhabit still water are often physiologically adapted to an environment with reduced oxygen. Some insects have their legs adapted to swimming organs.
2) Soil Insects. There are numerous species of insects that have become specialized to inhabit soil. Springtails, beetles, termites, ants, and fly larvae are notable groups with soil-inhabiting members. Insects may ingest organic material near the soil surface and defecate organic remains deeper into the soil, thereby contributing to the process by which litter is transformed. Excavation by soil insects also alters the soil, mixing layers and creating pores where oxygen can be present.
Structural features of soil insects include reduction of wings and presence of a body that is round in cross section. Sometimes the forelegs are modified for digging. Mating often occurs above the ground during brief periods. Eyes and antennae may be reduced or absent.
Insects inhabit almost every imaginable habitat, including plants, wood, stored food products, and living animal tissue (parasitic insects).
Examine the material on display to become familiar with examples of adaptation and radiation of insects into different habitats.
Insect Adaptations to Low Temperatures
In addition to the problems posed by ice formation, there are also significant problems that must be solved for normal metabolism to occur at low temperatures. The maintenance of neural function, fluidity of cell membranes, pH control, activity of enzymes, adaptation to hypoxia, dehydration of body fluids, etc. all present obstacles to low temperature survival. Although these difficulties are formidable, they will not be discussed further here, as the adaptations to freezing temperatures are the focus of this chapter.
Very few insect species are actually exposed to the full rigors of winter temperatures as most choose an overwintering microhabitat that provides a buffered temperature. The habitats provided inside vegetation (logs, stumps, etc.) or under the soil provide thermal buffering, especially when covered with snow. In many climates, however, the organisms are still exposed to potentially lethal conditions throughout the winter. The particular adaptations associated with freeze tolerance and freeze avoidance allow these organisms to survive in such harsh environments.