Insect Diversity & Orders – Comprehensive Exam Notes

Ecological Significance of Insects

• Jonas Salk quote:

  • “If all the insects were to disappear … within 50 years all life on earth would end.”

  • “If all human beings disappeared … within 50 years all forms of life would flourish.”

• Insects constitute > 1 million described species (over 50 % of all animal species).

• Provide essential ecosystem services: pollination, decomposition, soil aeration, biological control, nutrient cycling.

Basic Morphology & Definition

• Phylum Arthropoda ➔ Sub-phylum Hexapoda ➔ Class Insecta.

• Name “Insectum” = “cut up” ➔ body divided into three tagmata:

  • Head (antennae, compound eyes, mouthparts)

  • Thorax (three pairs of legs = Hexapoda + usually 2 pairs of wings)

  • Abdomen (usually 11 segments, spiracles, genitalia)

• Exoskeleton made of chitin (polysaccharide) – structural support analogous to vertebrate skeleton.

Distinguishing Insects From Look-Alikes

• Key diagnostic trait = exactly 3 pairs of jointed legs.

• Non-insect arthropods & leg counts:

  • Centipedes & millipedes – numerous legs.

  • Sowbugs (Isopoda) – 7 pairs.

  • Spiders & mites (Arachnida) – ⁵

  • 4 pairs.

High-Level Classification Snapshot

• Domain: Eukaryota; Kingdom: Animalia; Phylum: Arthropoda; Clade: Allotriocarida; Sub-phylum: Hexapoda; Class: Insecta.

• Sister “Class Entognatha” (Protura, Diplura, Collembola): apterous hexapods with entognathous (internal) mouthparts.

• 29 currently recognised insect orders (morphology + molecular phylogenetics).

Selected Primitive Orders (Apterygota & Palaeoptera)

• Archaeognatha (bristletails): hump-backed, wingless jumpers.

• Zygentoma (silverfish): flat, fast, long cerci.

• Ephemeroptera (mayflies): short-lived adults, subimago stage, long caudal filaments.

• Odonata (dragonflies & damselflies): aquatic nymphs, predatory adults, large eyes.

Polyneoptera & Paraneoptera Sampling

• Orthoptera, Dermaptera, Blattodea, Mantodea, Phasmatodea, Grylloblattodea, Mantophasmatodea, Plecoptera, Embioptera, Zoraptera.

• Hemiptera, Thysanoptera, Psocoptera, Phthiraptera (ectoparasitic lice).

ENDOPTERYGOTA (Holometabola) — Representative Major Orders

• Coleoptera, Lepidoptera, Diptera, Hymenoptera, Neuroptera, Megaloptera, Raphidioptera, Siphonaptera, Trichoptera, Strepsiptera, Mecoptera.

ORDER : COLEOPTERA (Beetles & Weevils)

• Largest order: ≈ 40 % of all insects; fore-wings hardened into elytra meeting in mid-line; hind-wings folded beneath.

• Occupy terrestrial + aquatic habitats; diets = predatory, herbivorous, fungivorous, detritivorous.

Ecological Guilds & Family Examples

• Predators:

  • Coccinellidae (ladybirds)

  • Carabidae (ground, tiger beetles)

  • Dytiscidae (diving beetles)

  • Gyrinidae (whirligigs – 4 eyes: split cornea for above/below water vision)

• Herbivores / Pests:

  • Chrysomelidae (leaf beetles)

  • Scarabaeidae (chafers, scarabs) – lamellate antennae, dung recycling

  • Cerambycidae (long-horns) – wood-boring larvae

  • Elateridae (click beetles – wireworm larvae)

  • Buprestidae (metallic wood borers)

Iconic Species & Phenomena

• Diabolical ironclad beetle (Phloeodes diabolicus): elytra withstand $39{,}000$ × body mass ➔ biomimetic inspiration.

• Bombardier beetles (Carabidae): exothermic quinone–peroxide spray “pulsed chemical rocket”.

• Stag beetles (Lucanidae): males’ super-mandibles; high collector prices (US$5k–70k$).

• Boll weevil monument (Enterprise, Alabama) — pest forced crop diversification (groundnut) → prosperity.

• Size extremes:

  • Smallest Nanosella fungi (0.25 mm)

  • Largest Goliathus giganteus (10 cm).

• Bioluminescence: Lampyridae (fireflies) & Phengodidae (glow-worms).

• Cultural notes: Egyptian sacred scarab (Scarabaeus sacer); Spanish fly (Lytta vesicatoria) source of cantharidin.

ORDER : LEPIDOPTERA (Butterflies & Moths)

• Name from Greek “lepido” (scale) + “ptera” (wings) – scales cover wings/body.

• Complete metamorphosis: egg → larva (caterpillar, eruciform) → pupa (chrysalis/cocoon) → adult.

• Mouthparts: elongated proboscis (straw-like); larvae with chewing mandibles + up to 5 pairs of prolegs bearing crochets.

• Wing-coupling: frenate, jugate, or amplexiform mechanisms.

• Defensive larval organs:

  • Osmeterium (Papilionidae) – eversible, malodorous.

  • Repugnatorial glands; urticating setae.

Butterfly Families & Traits

• Nymphalidae (brush-footed): fore-legs reduced; monarch migrations; cardiac-glycoside sequestration.

• Papilionidae (swallowtails): tail extensions; bird-dropping mimicry in early instars.

• Pieridae (whites/sulfurs): migratory; cabbage butterfly pest.

• Lycaenidae (blues/coppers): ant symbiosis, minute species (Grass jewel).

• Hesperiidae (skippers): hooked antennal club, rapid flight.

Moth Families of Economic Note

• Tineidae (clothes), Gelechiidae (grain, pink bollworm), Sesiidae (clearwings), Tortricidae (codling), Pyralidae (snout moths – Indian-meal), Geometridae (inchworms), Lasiocampidae (tent caterpillars), Saturniidae (silk moths), Sphingidae (hornworms), Erebidae, Noctuidae (armyworms, cutworms).

Behavioural & Evolutionary Highlights

• Bat–moth arms race: tympanal hearing (Noctuidae, Arctiidae); sonar jamming by tiger moth Bertholdia trigona; sound-absorbing Luna moth tails.

• Alkaloid pharmacophagy (male Nymphalids) ➔ defence + pheromone precursors.

• Mud-puddling for Na⁺, amino acids (esp. males).

• Record sizes: Queen Alexandra’s birdwing (largest butterfly); Atlas moth (largest moth); Himalayan golden birdwing (largest Indian butterfly); Kaiser-i-Hind prized collectible.

ORDER : NEUROPTERA (Lacewings, Antlions, Owlflies, Mantisflies)

• Holometabolous; two suborders: Hemerobiiformia & Myrmeleontiformia.

• General traits: net-veined wings, predatory larvae with sickle mandible-maxillae.

• Antlion larvae (doodlebugs) construct conical sand pits; lacewing larvae (aphidlions) prey on aphids.

• Notable biology:

  • Eggs on stalks (once misidentified as fungal Ascophora ovalis).

  • Larval “trash-carriers” camouflaged with prey remains or debris.

  • Hearing organs in Chrysopinae wing veins (bat detection).

  • Meconium (stored larval waste) expelled at adult eclosion.

  • Silk from Malpighian tubules, spun via anus.

• Families & Uses: Chrysopidae (green lacewings) mass-reared biocontrol; Mantispidae (mantidflies) parasitoids; Myrmeleontidae (antlions); Ascalaphidae (owlflies).

ORDER : HEMIPTERA (True Bugs & Homopterans)

Heteroptera (True Bugs)

• Hemelytra = basal leathery + apical membranous; wings cross in X-pattern; beak arises front of head.

• Aquatic, semi-aquatic, terrestrial; predators, herbivores, ectoparasites.

• Families & Notes:

  • Miridae (plant/predator bugs)

  • Pentatomidae (stink bugs) – spined soldier bug beneficial, “man-faced” species.

  • Reduviidae (assassin bugs) – Triatoma vectors Chagas; ambush bugs.

  • Cimicidae (bed/bat bugs) – ectoparasites.

  • Aquatics: Gerridae (water striders, incl. marine Halobates), Notonectidae (backswimmers), Belostomatidae (giant water bugs), Nepidae (water scorpions).

Homoptera (Auchenorrhyncha + Sternorrhyncha)

• Uniform wing texture; beak arises posteriorly; wings tent-like.

• Digestive filter chamber; honeydew excretion.

• Diverse life cycles:

  • Cicadas (up to 17-yr), leafhoppers, treehoppers, spittlebugs, planthoppers.

  • Psyllids, whiteflies (Aleyrodidae), aphids (Aphididae – parthenogenesis, wing polyphenism), scale insects (Coccidae) incl. lac (Kerria lacca) & cochineal (Dactylopius coccus).

• Trivia: honeydew of Trabutina mannipara posited as Biblical “manna”; ground-pearls (Margarodidae) form golden wax cysts.

ORDER : DIPTERA (True Flies, Mosquitoes, Gnats)

• One pair of membranous wings; hind-wings ➔ halteres (gyroscopic organs).

• Mouthparts haustellate: piercing–sucking (mosquito), sponging (housefly).

• Larvae legless maggots.

• Suborders: Nematocera (multi-segmented antennae), Brachycera (stylate), Cyclorrhapha (aristate).

Functional Guilds / Families

• Decomposers: Calliphoridae, Sarcophagidae, Muscidae.

• Dung feeders: Scathophagidae.

• Fungivores: Mycetophilidae.

• Phytophages: Agromyzidae (leaf-miners), Tephritidae (fruit flies), Cecidomyiidae.

• Predators: Syrphidae larvae, Asilidae adults.

• Parasitoids: Tachinidae, Conopidae.

• Blood feeders: Culicidae, Tabanidae, Simuliidae, Phlebotomidae.

• Aquatic larvae: Culicidae, Simuliidae, Chironomidae.

Notable Facts

• Extreme habitats:

  • Ephydra brucei in 112 °F hot springs.

  • Helaeomyia petrolei in crude oil.

  • Brine flies (Ephydra) dive in hypersaline waters with air bubble.

• Phorid Megaselia scalaris breeds in formalin, lung tissue.

• Antennal arista functions as air-speed indicator.

ORDER : ORTHOPTERA (Grasshoppers, Crickets, Katydids)

• Hind femora enlarged for jumping; tegmina thick, parallel-sided; hemimetabolous.

• Suborders:

  • Caelifera (short-horned grasshoppers & locusts) — families Acrididae, Tetrigidae, Pyrgomorphidae.

  • Ensifera (crickets & katydids) — families Gryllidae, Gryllotalpidae, Tettigoniidae, Rhaphidophoridae, Mogoplistidae.

Sound & Hearing

• Stridulation: file–scraper system; species-specific songs; some ultrasonic.

• Tympanal organs on fore-tibia (crickets/katydids) or first abdominal segment (grasshoppers).

• Snowy tree cricket “thermometer”: $T(°F)= ext{chirps in 15 s}+40$.

Economic/Medical Notes

• Locust plagues devastate crops.

• Mole crickets damage turf.

• Red-legged grasshopper (Melanoplus femurrubrum) intermediate host of poultry tapeworm Choanotaenia infundibulum.

ORDER : HYMENOPTERA (Bees, Wasps, Ants, Sawflies)

• Holometabolous; hind-wings linked to forewings via hamuli; chewing-lapping mouthparts; in Apocrita a distinct wasp-waist.

• Sex determination: haplodiploidy – females diploid (fertilised), males haploid (unfertilised); females can control sex ratio.

Symphyta (Sawflies & Horntails)

• Broad waist; phytophagous larvae; families Tenthredinidae, Cimbicidae, Siricidae (wood-borers).

Apocrita

Superfamily Formicoidea – Ants (Formicidae)

• Eusocial castes (queen, workers, males); elbowed antennae, petiole node(s).

• Interesting behaviours: slave-making ants; fungal gardeners (Attini); honey-pot ants store nectar.

Superfamily Apoidea – Bees & Some Wasps

• Pollinators par excellence.

• Families: Apidae (honey, bumble, carpenter), Megachilidae (leaf-cutter, mason – scopa on metasoma), Andrenidae (mining), Halictidae (sweat bees — salt-seeking behaviour).

• “Vulture bees” (Trigona hypogea, T. necrophaga, T. crassipes) feed on carrion, unique gut microbiome.

• Bee hotels: artificial nesting tunnels for solitary bees/wasps; promote urban pollinators.

Superfamily Vespoidea – Wasps & Ants

• Vespidae (paper wasps, hornets – social), Mutillidae (velvet ants – wingless females, painful sting), Pompilidae (spider wasps), Scoliidae, Tiphiidae (parasitoids of beetle larvae).

Parasitic Tiny Wasps (Biocontrol)

• Ichneumonidae, Braconidae, Chalcididae, Encyrtidae, Trichogrammatidae, Mymaridae (fairyflies – smallest insects; Kikiki huna in India; Dicopomorpha echmepterygis < 0.2 mm).

• Cuckoo wasps (Chrysididae) kleptoparasitize nests.

• Fig wasps (Agaoninae) exclusive pollinators of figs.

ORDER : ODONATA (Dragonflies & Damselflies)

• Large, predatory; aquatic naiads with extensible labial “mask”; hemimetabolous.

• Dragonflies (Anisoptera): robust body, broader hind-wings, wings held open at rest; damselflies (Zygoptera): slender, equal wings, held closed.

• Eyes: dragonflies often contiguous; damselflies separated.

• Families snapshot:

  • Zygoptera: Coenagrionidae, Lestidae, Calopterygidae, Platycnemididae.

  • Anisoptera: Libellulidae (skimmers), Aeshnidae (darners), Gomphidae (clubtails), Corduliidae (emeralds), Macromiidae (cruisers), Petaluridae (primitive petaltails).

• Special notes:

  • Male secondary genitalia on segment 2; “wheel” mating.

  • Jet propulsion via rectal chamber in naiads.

  • Massive migrations – Pantala flavescens longest (> 7,000 km trans-oceanic).

  • Vector of poultry trematode Prosthogonimus pellucidus.

ORDER : DICTYOPTERA COMPLEX

Blattodea – Cockroaches

• Flattened body, running legs, shield-like pronotum, ootheca egg case.

• Common domestic pests: Blattella germanica (German), Periplaneta americana (American – actually African origin), Blatta orientalis (Oriental), Supella longipalpa (brown-banded).

• Families: Blattidae, Ectobiidae, Blaberidae (hissing cockroaches, feeder insects), Corydiidae (sand rocaches), Cryptocercidae (wood roaches – termite relatives).

• Roles: decomposers; some commensal with ants; vectors of allergens & pathogens; intermediate hosts of poultry nematode.

Mantodea – Mantids / “Praying Mantises”

• Raptorial fore-legs, rotating triangular head, camouflage.

• Families: Mantidae (typical), Empusidae (conehead), Hymenopodidae (flower mantids), Deroplatyidae (dead-leaf), Amorphoscelididae.

• Behaviour: sexual cannibalism (more frequent in captivity), predation even on vertebrates; only insects able to rotate head laterally.

Phasmatodea – Stick & Leaf Insects (Phasmids)

• Extreme crypsis; prothorax short; wings often absent; eggs seed-like tossed to ground; some parthenogenesis; leg autotomy + regeneration; colour-change with environment; longest insect Phryganistria chinensis (> 60 cm).

• Families: Phasmatidae (sticks), Phylliidae (leaf insects).

Livelihoods & Economic Products From Insects

• Apiculture: global honey market ≈ $9\text{ billion}$; products – honey, beeswax, propolis, royal jelly, venom, beehive air, apilarnil.

• Lac culture: Kerria lacca on Palas, Ber, Kusum; shellac (varnish, electronics), dye, wax; India top producer (Jharkhand, Chhattisgarh, WB).

• Edible insects: projected market > $8\text{ billion}$ by 2030; rural nutrition & income.

• Specimen trade: rare butterflies/beetles fetch thousands (e.g., stag beetles US$70k).

• Cordyceps (Yarsagumba): parasitic fungus on ghost moth larvae; harvested in Himalayas; price $5–20\text{ lakh kg}^{-1}$; sustainability concerns.

Mathematical & Chemical References (for clarity)

• Force resistance of diabolical ironclad beetle ≈ $39{,}000\times$ its body weight.

• Snowy tree cricket temperature rule: $T<em>{°F}=N</em>{15s}+40$.

Cross-Order Connections & Themes

• Convergent evolution of sonar countermeasures: Lacewings & moths vs. bats.

• Repeated use of chemical defence: bombardier beetles (quinone spray), lepidopteran osmeterium, Hymenopteran sting/venom.

• Biomimicry inspirations: beetle elytra mechanics, bombardier propulsion, dragonfly wing aerodynamics.

• Ecosystem engineers: dung beetles in nutrient cycling; termites (Blattodea) in soil formation; ants in seed dispersal.

• Sociality continuum from solitary wasps to eusocial ants & bees ➔ haplodiploidy underpinning.

Ethical & Conservation Notes

• Over-collection (e.g., Kaiser-i-Hind, Morpho) leading to endangered listings.

• Habitat loss threatens migratory butterflies (Monarch), endemic Odonata.

• Sustainable utilisation (e.g., bee hotels, biocontrol releases) balances economic benefit with biodiversity.