PTERYGOTA

Exopterygota (Hemimetabola)

• Mallophaga - Biting lice
• Siphunculata - Sucking lice (syn. Anoplura)
• Hemiptera - True bugs
• Euphemeroptera - May flies
• Odonata - Dragonflies
• Dictyoptera - Cockroaches and Mantids
• Isoptera - Termites
• Plecoptera - Stoneflies
• Grylloblattodea - Rock crawlers
• Phasmida - Stick and Leaf-insects
• Orthoptera - Crickets and Grasshoppers
• Embioptera - Webspinners
• Zoroptera - (small rare group - no common name)
• Thysanoptera - Thrips
• Psocoptera - Book lice

• Group includes all insects with wings and those considered to be secondarily apterous (i.e. at some point in evolutionary history winged forms have occured). (B502)
• Young (usually called nymphs) very similar to parents. (B502)
• wings appear as pads developing externally on the thorax in the later stages of nyphal life. (B502)
• Rarely a resting stage or pupa and changes that occur when the nymph becomes an adult are usually termed "partial metamophosis". (B502)
• Adult stage may change habitat. (B502)

Endopterygota (Holometabola)

• Diptera - True flies
• Siphonaptera - Fleas (syn. Aphaniptera)
• Neuroptera - Lace wings
• Mecoptera - Scorpionflies
• Tricoptera - Caddisflies
• Lepidoptera - Butterflies and Moths
• Hymenoptera - Wasps, bees and ants
• Coleoptera - Beetles
• Dermaptera - Earwigs

• Young (usually called larvae) bear little resemblance to parents. (B502)
• Change from larva to adult is complex. (B502)
• a "resting stage" always present; insect does not feed and is apparently quiescent whilst great internal changes occur. (B502)
• Wings develop internally in the larva and become visible externally during the pupa stage. (B502)
• The changes from larva to adult are termed "complete metamorphosis. (B502)

APTERYGOTA

• Thysanura - Silver fish, bristle tails
• Diplura - Campodeids
• Protura - Myrientoma
• Collembola - Spring-tails

• Wingless insects, primitive structure, virtually no metamorphosis. (B502)

General Features

• Body
  • divided into three regions:
    • head
    • thorax
    • abdomen

    (B502)

  • outer protective covering (chitinous cuticle) serves as an exoskeleton for body covering and attachment of muscles. (B503)
  • chitinous cuticle is secreted by hypodermis (layer of single columnar epithelial cells). (B503)
  • chitinous cuticle is covered by the epicuticle (a thin lipoidal surface layer) which is permeable to lipids, but not water. (B503)
  • chitinous cuticle is molted (ecdysis) at intervals for the purposes of growth and metamorphosis; the hypodermis lays a new elastic cuticle under the old one which then splits allowing the insect to emerge. This process divides the life of the individual insect into a series of stages or instars (B503)
  • thick plates of cuticle are connected by much thinner section to allow movement and a degree of expansion (e.g. for egg laying). (B503)
  • muscles are striated and may be capable of extreme movement. (B503)
• Head:
  • consists of a variable number of fused segments. (B503)
  • one pair of antennae only (rarely no antennae). (B502)
  • one pair of maxillae. (B502)
  • one pair of mandibles. (B502)
  • a labium (formed by the medial fusion of a second pair of maxillae). (B502)
  • a hypopharynx. (B502)
• Thorax
  • consists of three segments - pro-, meso- and metathorax. (B503)
  • usually three pairs of legs, one on each thoracic segment. (B502)
  • a few insects are legless, and some larvae posses additional leglike appendages (e.g. prolegs) on the abdominal segments. (B502)
• Abdomen:
  • consists of 11 or fewer segments. (B503)
  • no walking appendages (except in some primitive hexapods). (B502)
  • other appendages (if present) occur at apex and consist of a pair of cerci, an ectoproct, and a pair of paraprocts. (B502)
  • terminal segments of abdomen are modified for copulation or egg-laying. (B503)
  • gonopore (external opening of the reproductive organs) on the posterior portion. (B502)
• Reproduction:
  • Flagellum of spermatozoa has microtubule arrangement of 9 + 9 + 2. (B502)
• Respiration:
  • spiracles (external openings) along sides of body connected to ramifying tubes or tracheae. (B502)