Insect Mouthparts Overview

Mouthparts:

• Types: chewing, piercing and sucking, sponging, rasping and sucking, chewing and lapping, siphoning
• Chewing:
  • primitive
  • Includes: grasshoppers, locusts, cockroaches, praying mantis, beetles
  • Mouthparts: labrum, labium, 2 mandibles, 2 maxilla
  • Labia and maxilla have sensory palps for tasting
• Piercing and sucking:
  • modified
  • Includes: cicadas, true bugs, flies
  • 2 mandibles and 2 maxilla form sharp, pointed tube called proboscis (enclosed in labium sheath)
• Mosquito specific:
  • Modified piercing and sucking
  • Labrum, 2 mandibles, 2 maxilla, and hypopharynx form 6 stylets pierce skin during blood feeding
  • Enclosed in labium sheath, stylets come out during feeding
  • Saliva: antihemostatic, anticoagulant, vaso-dialator for continuous blood supply
• Bees and wasps:
  • Chewing and lapping (modified)
  • Maxillae + labium form sucking tube (proboscis)
  • Saliva used to discharge nectar
• Hemiptera mouthparts:
  • Used for eating, cleaning, manipulating objects, molting
• Butterflies & moths:
  • Siphoning (modified)
• Horsefly:
  • Maxillae form sucking tube (proboscis)
  • No mandibles or hypopharynx, reduced labium and labial palps
• Housefly:
  • Piercing and sucking
  • Curved mandibles slash into skin
  • Sharp and pointed maxilla drill into host
  • Labium forms sponge to suck blood
• Sponging:
  • Labium forms sponge
  • No mandibles
  • Maxilla have unjointed maxillary palps

Thorax:

• Composed of prothorax, mesothorax, metathorax
• Each thoracic segment:
  • bears one pair of legs
  • meso and metathoracic segments each bear a pair of wings
• Divided into:
  • Dorsal plate: notum (top)
  • Ventral plate: sternum (bottom)
  • Lateral plates: pleuron (side)

Notum:

• Divided into 2 regions:
  • Alinotum: bears wings, divided into 3 regions: prescutum, scutum, scutellum (posterior)
  • Postnotum: bears phragma (intersegmental fort), flight muscles attached

Sternum:

• Divided into 3 regions:
  • Presternum
  • Basisternum
  • Sternellum
  • Spinesternum: 2 plates divided by pleural suture (strengthens side of thorax)
  • Ventral end of pleural suture articulates with coxa of leg
  • Pleural suture runs dorsally and articulates with pleural wing process: finger-like plate, serves as fulcrum for base of wing

Episternum:

• Lateral plate on thorax

Epimeron:

• Lateral plate on thorax

Legs:

• 3 pairs on each thoracic segment
• Each leg composed of 5 structural segments: coxa, trochanter, femur, tibia, tarsus
• Coxa: proximal segment, heavy, round, short
• Trochanter: provides wide range of motion
• Femur: muscular, powerful
• Tibia: lined with spines, kicking device
• Tarsus: divided into 5 segments, 'tarsomeres', last segment is 'pretarsus' with claws

Modified legs:

• Grasshoppers, locusts: legs modified for jumping
• Praying mantis: forelegs modified for grasping
• Mole crickets: forelegs modified for digging
• Giant waterbug: hindlegs modified for swimming
• Cockroach legs modified for running

Other notable points:

• Insects with larval stage: short fleshy legs present on one or more abdominal segments, not true legs, true legs only on insect thorax
• Swimming: aquatic Hemiptera and Coleoptera
• Jumping: Orthoptera, some Hemiptera, fleas
• Grasping prey: mantids, giant water bug
• Grasping hosts: lice, ectoparasites
• Digging: scarab beetles, some crickets
• Sound production: some grasshoppers
• Cleaning, carrying pollen: honeybee
• Defense: some leaf insects
• Insect nutrition: 10 essential amino acids, some insects spare deficient amino acids

Reproduction:

• Mate location:
  • On host: Strepsiptera (female legless, wingless, internal parasites of bees)
  • At food source: face flies (attracted to cowpies)
  • Lek behaviour: males defend territories on common mating ground
• Courtship:
  • Giving gifts or empty box
  • Females take males on long flights to test fitness
• Visual displays: butterfly courtship, fireflies (light emissions), fruit flies
• Chemical attractants: (pheromones), best studied in moths
• Sound production: stridulation in Orthoptera (crickets) and some aquatic Hemiptera, male mosquitos attracted to female wingbeat frequency

Molting:

• 3 step process:
  • Apolysis: separation of epidermis from cuticle
  • Ecdysis: casting off the old cuticle
  • Sclerotization: chemical hardening of the exocuticle
• Insect is called 'pharate' before ecdysis, 'exuvium' is the cast cuticle
• Insect called 'teneral' until sclerotization complete

Integument layers:

• Epicuticle: waterproof layer
• Exocuticle: hardened by sclerotization
• Endocuticle: not sclerotized, resorbed during molting
• Epidermis: produces all above layers

Excretory system:

• Organisms of excretion: Malpighian tubules and hindgut
• Euryhaline insects tolerant of wide salinity ranges
• Stenohaline insects intolerant of wide salinity ranges
• Cryptonephridium:
  • Malpighian tubules extend into rectal lumen
  • Water is drawn back from the rectum into the hemolymph
  • Important for keeping water in arid habitats
• Excretory process: uric acid is the major product of excretary system
• Toxic compounds:
  • Sequestered
  • Used for nutrients
  • Used for pheromone synthesis
  • Eliminated from body
• Hormones:
  • Diuretic hormone (DH):
    • synthesized in brain (median neurosecretory cells - mNSC)
    • stored in corpora cardiaca (CC)
    • causes diuresis
  • Antidiuretic hormone (ADH):
    • synthesized in brain (mNSC)
    • stored in CC
    • causes rectal absorption of water
  • Both hormones triggered by changing water balance
  • ADH controls the uptake of water from the rectum. These hormones help insects to efficiently utilize water in different conditions.

Salivary glands:

• Important in piercing and sucking mouthparts
• Blood-feeding: Saliva includes local anesthetics, vasodilators, anticoagulants
• Plant-feeding: Saliva contains digestive enzymes (amylase or invertase)
• Aphid saliva: pectinases for stylet penetration of vascular plant tissues

Microbial symbionts:

• Many insects need them for adequate nutrition
• Transferred on eggshells, eaten by neonates
• Examples:
  • Wood wasps (Siricidae) acquire sequestered cellulases from fungi
  • Lower termites (wood feeders) need cellulase activity from enteric protozoa and bacteria

This quiz explores the various types of insect mouthparts, including chewing, piercing and sucking, sponging, and others. Examine specific examples of insects, their anatomical features, and the functions these mouthparts perform, particularly in feeding processes. Test your knowledge on how these adaptations affect insect behavior and ecology.