Unit5 - Subjective Questions
ENT102 • Practice Questions with Detailed Answers
Discuss the Binomial Nomenclature system proposed by Carolus Linnaeus. What are the rules governing the scientific naming of insects?
Binomial Nomenclature is the system of naming organisms using a two-part scientific name, introduced by Carolus Linnaeus in the 10th edition of Systema Naturae (1758).
Key Rules (ICZN - International Code of Zoological Nomenclature):
- Two Parts: Every scientific name consists of two words: the Genus (generic name) and the Species (specific epithet).
- Language: Names must be in Latin or Latinized.
- Capitalization: The first letter of the Genus is always Capitalized, while the species name is always written in lowercase.
- Formatting: When typed, the name must be italicized (e.g., Musca domestica). When handwritten, it must be underlined separately (e.g., \underline{Musca} \underline{domestica}).
- Author Citation: The name of the author who first described the species is often written after the species name without italics (e.g., Musca domestica Linnaeus).
- Priority: The valid name of a taxon is the oldest available name applied to it (Law of Priority).
Define the following taxonomic categories: Species, Genus, Family, and Order.
- Species: The fundamental unit of taxonomy. It is a group of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups. They share common morphological and physiological characteristics.
- Genus: A taxonomic rank used in the biological classification of living and fossil organisms to group closely related species. For example, Apis is the genus for honey bees.
- Family: A taxonomic rank between Order and Genus. Family names in animals usually end in the suffix -idae (e.g., Acrididae). It groups related genera sharing specific common traits.
- Order: A higher taxonomic rank used to classify families that exhibit similar basic characteristics (e.g., wing structure, metamorphosis type). For example, insects with hard forewings are grouped in the Order Coleoptera.
Differentiate between Biotype and Sub-species with examples.
| Feature | Sub-species | Biotype |
|---|---|---|
| Definition | A population of a species that is geographically isolated and morphologically distinct from other populations of the same species. | A population within a species that is morphologically similar to other populations but differs in physiological traits (host preference, resistance to pesticides). |
| Basis | Based on Geography and Morphology. | Based on Physiology or Genetics (often host-specific). |
| Nomenclature | Given a trinominal name (e.g., Apis mellifera scutellata). | Usually designated by numbers or letters (e.g., Brown planthopper Biotype 1, 2). |
| Stability | Relatively stable evolutionary unit. | Can change rapidly due to selection pressure (e.g., introduction of resistant crop varieties). |
Explain the general classification of the Class Insecta based on the presence of wings and type of metamorphosis.
The Class Insecta is broadly classified into two Subclasses based on the presence of wings:
1. Subclass: Apterygota (Ametabola)
- Wings: Primarily wingless (primitive condition).
- Metamorphosis: Ametabolous (No metamorphosis; egg young adult).
- Examples: Thysanura (Silverfish), Collembola (Springtails).
2. Subclass: Pterygota (Metabola)
- Wings: Winged (or secondarily wingless).
- Metamorphosis: Present. Divided further into two divisions:
- Division Exopterygota (Hemimetabola): External wing development. Incomplete metamorphosis (Egg Nymph Adult). Examples: Orthoptera, Hemiptera.
- Division Endopterygota (Holometabola): Internal wing development. Complete metamorphosis (Egg Larva Pupa Adult). Examples: Coleoptera, Lepidoptera.
Describe the distinguishing characteristics of the Order Orthoptera and list the families of agricultural importance.
Characteristics of Order Orthoptera (Straight-winged insects):
- Wings: Forewings are leathery and thickened, called Tegmina. Hindwings are membranous and folded fan-like beneath the forewings.
- Mouthparts: Mandibulate (Chewing and biting type).
- Legs: Hind legs are usually modified for jumping (Saltatorial).
- Metamorphosis: Hemimetabolous (Gradual).
- Sound: Males often produce sound (stridulation).
Families of Agricultural Importance:
- Acrididae: Short-horned grasshoppers and locusts.
- Tettigoniidae: Long-horned grasshoppers/Katydids.
- Gryllidae: Crickets.
- Gryllotalpidae: Mole crickets.
Compare and contrast the families Acrididae and Tettigoniidae.
| Feature | Acrididae (Short-horned Grasshoppers) | Tettigoniidae (Long-horned Grasshoppers) |
|---|---|---|
| Antennae | Short, usually less than half the body length. | Very long, bristle-like, often exceeding body length. |
| Auditory Organs | Tympanum located on the first abdominal segment. | Tympanum located on the tibia of forelegs. |
| Ovipositor | Short and horny. | Long, sword-like, or sickle-shaped. |
| Stridulation | Rubbing hind femur against tegmina. | Rubbing the bases of the two tegmina together. |
| Habit | Diurnal (active during the day). | Nocturnal (active at night). |
| Diet | Herbivorous (major crop pests). | Herbivorous or Predatory. |
Write a short note on the family Gryllotalpidae emphasizing their morphological adaptations.
Family: Gryllotalpidae (Mole Crickets)
- Habitat: They are fossorial insects, living underground in burrows.
- Leg Modification: The forelegs are highly modified into Fossorial legs (digging type). The tibia and tarsus are flattened and toothed, acting like a shovel to cut through roots and soil.
- Body Shape: The body is stout, velvety, and cylindrical to move easily through tunnels.
- Head: Conical head to assist in pushing through soil.
- Wings: Tegmina are short; hind wings are long and extend beyond the abdomen.
- Importance: They are pests of root crops and turf grass, severing roots while digging.
Describe the key features of the Order Dictyoptera and distinguish between the families Mantidae and Blattidae.
Order Dictyoptera:
- Forewings are leathery tegmina; hindwings membranous.
- Eggs are laid in a protective case called an Ootheca.
Comparison:
1. Family Mantidae (Praying Mantids):
- Head: Triangular, highly mobile (can turn 180 degrees).
- Forelegs: Modified into Raptorial legs (grasping) for predation. Coxae are elongated.
- Prothorax: greatly elongated.
- Diet: Carnivorous (Predators of other insects).
2. Family Blattidae (Cockroaches):
- Head: Covered/concealed from above by a large shield-like Pronotum.
- Body: Dorso-ventrally flattened.
- Legs: Cursorial (running type) with spiny tibiae.
- Diet: Omnivorous/Scavengers.
Explain the social organization and caste system in the Order Isoptera (Termites), focusing on the family Termitidae.
Order Isoptera (Termites/White Ants):
Termites are eusocial insects living in colonies. The family Termitidae is the largest family of termites (higher termites).
Caste System:
- Reproductives (Royal Caste):
- King & Queen: Dealated adults responsible for reproduction. The Queen has a massive abdomen (physogastry) for laying thousands of eggs daily.
- Alates: Winged forms that swarm to start new colonies.
- Sterile Castes:
- Workers: Wingless, sterile, soft-bodied, blind. They forage, feed the queen/soldiers, and build the termitarium (nest). They cause the agricultural damage.
- Soldiers: Wingless, sterile, with large sclerotized heads and powerful mandibles (or nasus in some Termitidae). They defend the colony against enemies (e.g., ants).
Discuss the economic importance of the Order Odonata.
Order Odonata (Dragonflies and Damselflies)
- Predatory Nature: Adults are aerial predators, catching insects on the wing using a basket formed by their legs. Nymphs (called Naiads) are aquatic predators.
- Biological Control:
- Naiads: Feed voraciously on mosquito larvae in water bodies, helping control vectors of malaria and dengue.
- Adults: Feed on mosquitoes, flies, moths, and small hoppers in the field.
- Bio-indicators: Their presence often indicates good water quality.
- Pest Status: Generally beneficial, but naiads may occasionally prey on small fish fry in fisheries.
What are the unique morphological features of the Order Thysanoptera? Describe the family Thripidae.
Order Thysanoptera (Thrips/Fringe-wings):
- Wings: Long, narrow, with reduced venation and fringed with long marginal hairs (hence "fringe-winged").
- Mouthparts: Rasping and sucking type. Asymmetrical (right mandible is vestigial/absent; left mandible is functional).
- Tarsi: Have a bladder-like organ (arolium) at the tip, used for adhesion.
Family Thripidae:
- Includes the most economically important thrips (e.g., Thrips tabaci, Scirtothrips dorsalis).
- Ovipositor: Females have a saw-like ovipositor curved downwards.
- Damage: They lacerate plant tissues and suck oozing sap, causing "silvery streaks" or curling of leaves (Chilli leaf curl). They also vector viruses like Tospoviruses.
Distinguish between the two suborders of Hemiptera: Heteroptera and Homoptera.
| Feature | Heteroptera (True Bugs) | Homoptera (Hoppers, Aphids, Scales) |
|---|---|---|
| Forewings | Hemelytra: Basal half is hard/leathery, apical half is membranous. | Uniform texture throughout (either membranous or leathery). |
| Wing Position | Held flat over the abdomen at rest. | Held roof-like over the body at rest. |
| Beak Origin | Arises from the front of the head (gula is present). | Arises from the posterior of the head (gula is absent). |
| Head | Porrect (horizontal). | Opisthognathous (deflexed backward). |
| Examples | Pentatomidae, Coreidae, Cimicidae. | Cicadellidae, Aphididae, Aleurodidae. |
Write a descriptive note on the family Pentatomidae.
Family: Pentatomidae (Stink Bugs / Shield Bugs)
- Shape: Shield-shaped body.
- Antennae: 5-segmented (hence "Penta").
- Scutellum: The mesoscutellum is prominent and triangular, extending to the middle of the abdomen.
- Odor: Possess odoriferous glands opening laterally on the thorax, producing a foul smell for defense.
- Feeding:
- Most are phytophagous (plant feeders), e.g., Green Stink Bug (Nezara viridula).
- Some are predatory, feeding on caterpillars.
- Economic Importance: Major pests of rice, vegetables, and pulses.
Compare the families Coreidae and Pyrrhocoridae.
1. Family Coreidae (Squash Bugs / Leaf-footed Bugs):
- Wings: Membranous part of hemelytra has many veins.
- Head: Narrower than the pronotum.
- Odor: Have strong scent glands opening on the thorax.
- Legs: Hind tibiae are often expanded or leaf-like (leaf-footed).
- Example: Rice Earhead Bug (Leptocorisa acuta).
2. Family Pyrrhocoridae (Red Bugs / Stainers):
- Wings: Membranous part of hemelytra lacks closed cells at the base.
- Coloration: Usually brightly colored with red and black markings.
- Ocelli: Absent.
- Example: Red Cotton Bug (Dysdercus cingulatus), which stains cotton lint.
Describe the unique features of the family Aphididae and their significance in agriculture.
Family: Aphididae (Aphids / Plant Lice)
Morphological Features:
- Body: Small, soft-bodied, pear-shaped insects.
- Cornicles: A pair of tube-like structures on the dorsal side of the 5th or 6th abdominal segment. They secrete waxy fluids.
- Tail: A cauda is often present at the tip of the abdomen.
- Polymorphism: They exhibit various forms (winged/wingless, sexual/parthenogenetic) within the same species.
Agricultural Significance:
- Sap Sucking: Result in stunted growth and curling of leaves.
- Honeydew: They excrete sugary honeydew, which promotes the growth of Sooty Mould (fungus), hindering photosynthesis.
- Vectors: They are the most efficient vectors of plant viral diseases (e.g., Potato Virus Y).
Differentiate between Cicadellidae and Delphacidae.
| Feature | Cicadellidae (Leafhoppers / Jassids) | Delphacidae (Planthoppers) |
|---|---|---|
| Hind Tibia | Has a double row of spines extending the entire length. | Has a large, movable spur (calcar) at the distal end. |
| Antennae | Bristle-like, arising between the eyes. | Arise from notches beneath the eyes; thickened basal segments. |
| Movement | Move sideways or diagonally when disturbed. | Usually jump or move forward. |
| Examples | Cotton Jassid (Amrasca biguttula). | Brown Planthopper (Nilaparvata lugens). |
Explain the characteristics of the family Coccidae and Pseudococcidae.
1. Family Coccidae (Soft Scales):
- Covering: Body is covered by a hard, smooth, or waxy shell (exoskeleton itself hardens) which is inseparable from the insect body.
- Legs: Usually absent in sedentary adult females.
- Honeydew: Produce copious amounts of honeydew.
- Example: Green scale of coffee.
2. Family Pseudococcidae (Mealybugs):
- Covering: Body is soft, covered with powdery white waxy secretion (mealy appearance). Not a hard shell.
- Legs: Well-developed legs; mobile throughout life.
- Body: Distinctly segmented.
- Example: Papaya mealybug (Paracoccus marginatus).
Write a note on the family Aleurodidae.
Family: Aleurodidae (Whiteflies)
- Appearance: Minute insects; both sexes are winged. Wings and body are dusted with white waxy powder.
- Vasiform Orifice: A characteristic opening on the dorsal side of the last abdominal segment, covered by an operculum and containing a lingula. It is used to eject honeydew.
- Metamorphosis: Complex. The last nymphal instar is quiescent and is called a "Puparium" (though they are hemimetabolous).
- Damage: Direct sap sucking and vectoring viral diseases (e.g., Yellow Mosaic Virus).
- Example: Bemisia tabaci (Cotton whitefly).
Describe the family Neuroptera: Chrysopidae and its role in pest management.
Order Neuroptera (Nerve-winged insects), Family Chrysopidae (Green Lacewings):
Characteristics:
- Body: Delicate, pale green body.
- Wings: Large, transparent wings with net-like venation (reticulate). Held roof-like over the body.
- Eyes: Distinctive golden/copper-colored eyes (hence "Golden eyes").
- Eggs: Stalked eggs laid on leaves (to prevent cannibalism by larvae).
Role in Pest Management:
- The larvae are voracious predators known as "Aphid Lions."
- They have sickle-shaped, hollow mandibles to suck fluids from soft-bodied pests.
- They feed on aphids, mealybugs, whiteflies, and small caterpillars.
- They are widely used in Biological Control programs.
Briefly describe the family Cimicidae.
Family: Cimicidae (Bed Bugs)
- Habitat: Ectoparasites on mammals (including humans) and birds.
- Wings: Wingless (Apterous) or vestigial wing pads.
- Body: Dorso-ventrally flattened, reddish-brown, oval body (allows hiding in crevices).
- Feeding: Blood-sucking (Hematophagous). The beak fits into a groove on the prosternum.
- Behavior: Nocturnal. They possess stink glands.
- Example: Cimex lectularius (Common Bed Bug).