Insects

Primitive Insect:

• Cold blooded (ectothermic)

Built on 3 parts:

• Head
  • Two sets of eyes
    • Compound Eyes
    • ocelli
  • Mouths
  • Antennae
    • Often used to sniff the air for chemical compounds
      • E.g., food, mates
• Thorax
  • Movement
    • Where legs are attached (3 pairs)
    • Where wings are attached (typically 2 pairs)
• Abdomen
  • Where guts are located
  • Used for breathing

What makes an insect? The body plan...

• Three tagmata
  1. Head - Perception (vision, smell, taste), feeding
     • Most orders have developed certain types of adaptations
       • Specializations of each type of tagmata
     • Mouthparts
       1. Chewing (standard way of being)
          1. E.g., grasshopper
          2. Tiger beetle (Coleoptera)
       2. Piercing and sucking
          1. Mosquito (diptera)
       3. Siphoning
          1. Butterfly (lepidoptera)
          2. Fleas (Siphonaptera)
       4. Sponging
          1. House flies
  2. Thorax
     • Leg parts
       • Cursorial (running)
       • Fossorial (digging)
       • Raptorial (grasping)
       • Saltatorial (jumping)
       • Natatorial (swimming)
     • Wing Parts
       • Odonata
         • Primitive, 2 "equal" pair, membranous
       • Hemiptera
         • Forewings partially sclerotized (i.e. hardened)
       • Hymenoptera
         • Membranous, forewings larger than hindwings, held together by hamuli (small hooks)
       • Coleoptera
         • Forewings completely sclerotized
       • Lepidoptera
         • Forewings larger than hindwings, covered with scales
       • Diptera
         • Hindwings replaced by halteres
  3. Abdomen
     • Oviposition
       • (Hymenoptera: Icheneumonidae)
     • Defense/display
       • (Dermaptera: Labiduridae)
     • Display
       • (Coleoptera: Lampyridae)
     • Respiration/gills
       • (Odanata: Lestidae)

The exoskeleton:

• Prevent water loss
• protect from natural enemies
• Muscle attachment Cuticle (critical to success of insecta; contains chiten) Epidermis (cellular) Cuticle + epidermis = integument

Nervous system

• Largely decentralised
• Brain controls eyes, antennae, and mouthparts
• Thoricic (peripheral) ganglia control legs and wings
• Abdominal (peripheral) ganglia control gut and reproductive controls

Circulatory system

• Open ended system
• Nutrient transport
• Immune system
• Hydraulic mechanism
• Blood = hemolymph
• No thermoregulation
• Not involved in respiration

Digestive system

• A "one-way" system
• Foregut = breakdown of large food particles (using saliva)
• Midgut = enzymatic digestion
• Hindgut = fecal pellets and excretion

Respiratory system

• Completely dependent on passive diffusion
• O2 enters insect via spiracles, trachea, and tracheoles
• Diffuses into tissues
• Implications for body size

===== Herbivory and disturbance