Unit 6: Insect Systematics and Taxonomy II

Overview of Endopterygota (Holometabola)

The orders covered in this unit belong to the Division Endopterygota.

• Metamorphosis: Holometabolous (Complete: Egg Larva Pupa Adult).
• Wing Development: Internal wing development (wings develop inside the body during the larval stage).

Order 1: Lepidoptera (Scale Wings)

• Etymology: Lepido = Scale; ptera = Wings.
• General Characteristics:
  • Wings and body covered with overlapping scales (modified setae).
  • Mouthparts: Siphoning type (coiled proboscis) in adults; Chewing type in larvae (caterpillars).
  • Larvae: Called caterpillars; possess 3 pairs of thoracic legs and 2–5 pairs of abdominal prolegs with crochets (hook-like structures).
  • Pupa: Generally obtect (appendages glued to the body), often enclosed in a cocoon.

Important Families

1. Pieridae (Whites and Sulphurs)

• Diagnostic Features: Medium-sized butterflies; usually white, yellow, or orange with black markings. Tarsal claws are bifid (cleft).
• Larvae: Green or brown, sparsely hairy.
• Agricultural Importance:
  • Cabbage Butterfly (Pieris brassicae): A major pest of cruciferous vegetables (cabbage, cauliflower).

2. Papilionidae (Swallowtail Butterflies)

• Diagnostic Features: Large, colorful butterflies. Hind wings often possess a tail-like extension.
• Larvae: Smooth skin; possess an osmeterium (Y-shaped eversible gland behind the head) that emits a foul odor for defense.
• Agricultural Importance:
  • Citrus Butterfly (Papilio demoleus): Serious pest of citrus nurseries; larvae defoliate plants.

3. Noctuidae (Owlet Moths)

• Diagnostic Features: The largest family of Lepidoptera. Dull-colored, heavy-bodied night fliers. Forewings narrow and darker; hind wings broad and lighter.
• Larvae: Most have 5 pairs of prolegs, though some (semi-loopers) have fewer.
• Agricultural Importance: Contains some of the most destructive agricultural pests.
  • Helicoverpa armigera: Gram pod borer/Cotton bollworm (polyphagous).
  • Spodoptera litura: Tobacco caterpillar/Armyworm.
  • Agrotis spp.: Cutworms (cut seedlings at ground level).

4. Sphingidae (Hawk Moths / Sphinx Moths)

• Diagnostic Features: Medium to large moths. Body is stout, spindle-shaped (streamlined) for fast flight. Narrow, pointed forewings.
• Larvae: Known as "Hornworms" because they usually possess a distinct dorsal horn on the 8th abdominal segment.
• Agricultural Importance:
  • Tobacco Hornworm: Defoliator of tobacco.
  • Til (Sesame) Hawk Moth (Acherontia styx).

5. Pyralidae (Snout Moths)

• Diagnostic Features: Small, delicate moths. Labial palpi are long and project forward, resembling a snout.
• Agricultural Importance:
  • Stem Borers: Chilo partellus (Sorghum stem borer).
  • Stored Grain Pests: Corcyra cephalonica (Rice moth).
  • Vegetable Pests: Leucinodes orbonalis (Brinjal shoot and fruit borer).

6. Gelechiidae

• Diagnostic Features: Small moths. Labial palpi are long and up-curved over the head. Outer margin of the hind wing is often trapezoidal with a pointed apex.
• Agricultural Importance:
  • Pink Bollworm (Pectinophora gossypiella): Major pest of cotton.
  • Potato Tuber Moth (Phthorimaea operculella): Pest of potato in field and storage.
  • Angoumois Grain Moth (Sitotroga cerealella).

7. Arctiidae (Tiger Moths)

(Note: Now often classified as subfamily Arctiinae under family Erebidae)

• Diagnostic Features: Brightly colored (aposematic coloration).
• Larvae: Densely hairy, known as "Woolly Bears."
• Agricultural Importance:
  • Red Hairy Caterpillar (Amsacta moorei): Polyphagous root pest.
  • Bihar Hairy Caterpillar (Spilarctia obliqua): Defoliator of pulses and oilseeds.

8. Saturniidae (Giant Silkworm Moths)

• Diagnostic Features: Includes the largest moths. Antennae are bipectinate (feather-like), especially in males. Vestigial mouthparts (adults do not feed).
• Agricultural Importance:
  • Tussar Silk Moth (Antheraea paphia).
  • Eri Silk Moth (Samia cynthia ricini).

9. Bombycidae (Silkworm Moths)

• Diagnostic Features: Creamy white, heavy-bodied moths with weak flight. Bipectinate antennae.
• Agricultural Importance:
  • Mulberry Silkworm (Bombyx mori): Sole producer of commercial mulberry silk. Highly domesticated.

Order 2: Coleoptera (Sheath Wings)

• Etymology: Coleo = Sheath; ptera = Wings.
• General Characteristics:
  • Forewings: Modified into hard, sclerotized Elytra which meet in a straight line down the back.
  • Hindwings: Membranous, used for flight.
  • Mouthparts: Chewing type (mandibulate).
  • Largest order of insects.

Important Families

1. Coccinellidae (Ladybird Beetles)

• Diagnostic Features: Convex, hemispherical body (oval/round). Head partly concealed by the pronotum. Often brightly colored (red/orange) with black spots.
• Agricultural Importance:
  • Beneficial: Most are predators of aphids, mealybugs, and scale insects (e.g., Coccinella septempunctata).
  • Pest: Subfamily Epilachninae are phytophagous (e.g., Hadda beetle, Epilachna vigintioctopunctata, pest of brinjal and potato).

2. Chrysomelidae (Leaf Beetles)

• Diagnostic Features: Closely resemble ladybird beetles but are more oval and antennae are half the length of the body. Tarsi are pseudotetramerous (appear 4-segmented, actually 5).
• Agricultural Importance:
  • Red Pumpkin Beetle (Raphidopalpa foveicollis): Pest of cucurbits.
  • Colorado Potato Beetle: A major global pest.

3. Cerambycidae (Longicorn / Long-horned Beetles)

• Diagnostic Features: Antennae are usually longer than the body (filiform). Compound eyes are often notched at the base of the antennae.
• Larvae: Called "Round-headed borers."
• Agricultural Importance:
  • Mango Stem Borer (Batocera rufomaculata).
  • Coffee White Borer.

4. Curculionidae (Weevils / Snout Beetles)

• Diagnostic Features: Head prolonged into a distinct rostrum (snout) with mouthparts at the tip. Antennae are geniculate (elbowed) and clubbed.
• Agricultural Importance:
  • Rice Weevil (Sitophilus oryzae): Stored grain pest.
  • Red Palm Weevil (Rhynchophorus ferrugineus): Pest of coconut.
  • Cotton Boll Weevil.

5. Bruchidae (Pulse Beetles / Seed Weevils)

(Note: Now subfamily Bruchinae under Chrysomelidae)

• Diagnostic Features: Body short and stout. The elytra do not cover the tip of the abdomen (pygidium is exposed). Head is small.
• Agricultural Importance:
  • Pulse Beetle (Callosobruchus chinensis): Major pest of stored legumes (gram, moong, peas).

6. Scarabaeidae (Scarabs / Dung Beetles)

• Diagnostic Features: Antennae are lamellate (terminal segments expand into flat plates/leaves). Forelegs often modified for digging (fossorial).
• Larvae: C-shaped, fleshy "White Grubs."
• Agricultural Importance:
  • White Grubs (Holotrichia spp.): Polyphagous root feeders (groundnut, sugarcane).
  • Dung Beetles: Beneficial for nutrient recycling.
  • Rhinoceros Beetle (Oryctes rhinoceros): Pest of coconut.

Order 3: Hymenoptera (Membranous Wings)

• Etymology: Hymen = Membrane; ptera = Wings.
• General Characteristics:
  • Two pairs of membranous wings; hind wings smaller than forewings, interlocked by hooks called hamuli.
  • Mouthparts: Chewing or Chewing-Lapping.
  • Abdomen: First segment fused with thorax (propodeum); second segment constricted (petiole/waist) in Apocrita.
  • Ovipositor often modified into a sting or piercer.

Important Families

1. Tenthredinidae (Sawflies)

• Suborder: Symphyta (No waist).
• Diagnostic Features: Broad junction between thorax and abdomen (no wasp waist). Ovipositor saw-like for slitting plant tissue.
• Larvae: Resemble lepidopteran caterpillars but have 6–8 pairs of prolegs lacking crochets.
• Agricultural Importance:
  • Mustard Sawfly (Athalia lugens proxima): Pest of crucifers.

2. Apidae (Honey Bees, Bumble Bees)

• Diagnostic Features: Body hairy. Hind tibia modified into a corbicula (pollen basket) in workers. Tongue suited for lapping nectar.
• Agricultural Importance:
  • Pollination: Essential for crop fertilization.
  • Products: Honey and beeswax.
  • Apis mellifera (European bee), Apis cerana (Indian bee).

3. Trichogrammatidae

• Diagnostic Features: Minute, microscopic wasps (0.3–1 mm). Tarsi 3-segmented. Wings have rows of microscopic hairs.
• Agricultural Importance:
  • Egg Parasitoids: The genus Trichogramma is widely mass-reared and released for biological control of lepidopteran pests (e.g., sugarcane borers, cotton bollworms).

4. Ichneumonidae (Ichneumon Wasps)

• Diagnostic Features: Slender wasps with long filiform antennae (16+ segments). Wing venation includes a "horse-head" shaped cell. Long, permanently extruded ovipositor.
• Agricultural Importance:
  • Major parasitoids of caterpillars and beetle larvae. Beneficial for natural pest control.

5. Braconidae

• Diagnostic Features: Resemble Ichneumonids but generally smaller. Distinguished by wing venation (lack the second recurrent vein found in Ichneumonids).
• Agricultural Importance:
  • Important parasitoids.
  • Cotesia (= Apanteles) spp. (Larval parasitoid of bollworms).
  • Bracon spp. (Parasitoids of coconut black headed caterpillar).

6. Chalcididae

• Diagnostic Features: Small wasps (2–7 mm). Hind femora are greatly enlarged and toothed. Punctured/pitted thorax.
• Agricultural Importance:
  • Parasitoids of Lepidoptera and Diptera pupae. Can be primary parasitoids (beneficial) or hyperparasitoids (harmful to other beneficials).

Order 4: Diptera (Two Wings)

• Etymology: Di = Two; ptera = Wings.
• General Characteristics:
  • Forewings: Functional membranous wings.
  • Hindwings: Reduced to knob-like organs called halteres (balancing organs).
  • Mouthparts: Piercing-sucking, sponging, or cutting-sponging.
  • Larvae: Legless, known as maggots.

Important Families

1. Cecidomyiidae (Gall Midges)

• Diagnostic Features: Minute, delicate flies with long moniliform (bead-like) antennae. Reduced wing venation.
• Agricultural Importance:
  • Rice Gall Midge (Orseolia oryzae): Maggots bore into the central shoot of rice, causing "Silver Shoot" or "Onion Leaf" symptom.

2. Tachinidae (Tachinid Flies)

• Diagnostic Features: Resemble house flies but are larger and very bristly (especially on the abdomen). The arista (bristle on antenna) is bare (not plumose).
• Agricultural Importance:
  • Beneficial: Strictly parasitic. Larvae are endoparasites of Lepidopteran caterpillars and Coleopteran larvae.

3. Agromyzidae (Leaf Miner Flies)

• Diagnostic Features: Small to minute flies, often black or yellowish.
• Agricultural Importance:
  • Leaf Miners: Larvae mine between the epidermal layers of leaves, creating serpentine tunnels.
  • Liriomyza trifolii (Serpentine leaf miner).
  • Red gram pod fly (Melanagromyza obtusa).

4. Culicidae (Mosquitoes)

• Diagnostic Features: Slender body, long legs. Wings have scales on the veins and margins. Piercing-sucking mouthparts (females).
• Agricultural/Medical Importance:
  • Vectors of diseases (Malaria - Anopheles; Dengue/Chikungunya - Aedes; Filariasis - Culex).
  • Larvae (wrigglers) are aquatic.

5. Muscidae (House Flies)

• Diagnostic Features: Medium-sized. Sponging mouthparts (labellum). Arista is plumose (hairy) to the tip.
• Agricultural/Medical Importance:
  • House Fly (Musca domestica): Mechanical vector for typhoid, cholera, etc.
  • Stable Fly (Stomoxys calcitrans): Blood-sucking pest of livestock.

6. Tephritidae (Fruit Flies)

• Diagnostic Features: Wings are spotted or banded (patterned). The female has a sharp, retractable ovipositor.
• Agricultural Importance:
  • Major quarantine pests. Maggots feed on the pulp of ripening fruits, causing rotting.
  • Melon Fruit Fly (Bactrocera cucurbitae): Attacks cucurbits.
  • Oriental Fruit Fly (Bactrocera dorsalis): Attacks mango, guava.