Subclass Pterygota

Winged Insects

1. Ancestors had wings even if present day forms do not have wings e.g. fleas (Siphonaptera), lice (Phthiraptera)
2. Loss of wings can be understood through study of:
   • Most recent common ancestor had wings
   • Sister Group relationships (fleas and flies), (lice and bugs)
3. Loss of wings can occur at various taxonomic levels e.g.
   • Families within Orders have lost wings e.g. Stenopelmatidae (king crickets)
   • One sex within species lost wings e.g. Mutillidae (a family of wasps)
   • One sex within Order have lost wings e.g. Strepsiptera

Diagnostic Features

1. Wings restricted to mesothorax and metathorax.
2. Wings with venation.
3. Wings attached high on pleural wall.
4. Basal articulation with a complex of sclerites.
5. Internal apodeme from pleural wing process to base of coxa - for strength and muscle attachment

Two forms of Wing Development

1. Exopterygote
2. Endopterygote

Phylogeny

1. Three lineages of winged insects have survived
   • Ephemeroptera - Palaeoptera
   • Odonata - Palaeoptera
   • Neoptera - Remainder of Pterygotes
2. Palaeoptera:
   • Extensive venation, cannot fold wing down over abdomen
   • Some classifications put all forms, the Odonata and Ephemeroptera into the Palaeoptera.
   • Such a group may not be monophyletic.