University of Michigan Biological Station

Biology 442 - Biology of Insects

Lecture Notes - External Structure

1. Arthropod characteristics.
   1. Jointed exoskeleton with hard plates called sclerites and various articulations.
      1. Structure of exoskeleton; cuticle, chitin, tanning, sclerotization, epidermis, basement membrane.
      2. Sutures and sclerites.
   2. Segmentation (Tagmatazation).
   3. Basic unit.
      1. Dorsal tergum.
      2. Ventral sternum.
      3. Lateral pleuron.
      4. Jointed appendages between sternum and pleuron.
2. Insect characteristics.
   1. 3 segments - head, thorax, abdomen.
   2. 3 pairs of legs on thorax.
   3. 2 pairs of wings on thorax.
3. Head.
   1. Strongly sclerotized - thought to be made of 5 segments.
   2. Eyes; compound and ocelli.
   3. Antennae.
   4. Sutures and Sclerites.
      1. Frontoclypeal (epistomal); anterior tentorial pits.
      2. Subantennal, subocular.
      3. Frons, clypeus, vertex.
      4. Gena, subgena, postgena, occiput, postocciput.
      5. Subgenal, occipital, postoccipital, posterior tentorial pits.
      6. tentorium.
   5. Mouthparts.
      1. Labrum.
      2. Mandibles.
      3. Maxilla(e); cardo, stipes, galea, lacinia, palps.
      4. Labium; postmentum (submentum, mentum), prementum, ligula (glossa, paraglossa), palps.
      5. Hypopharynx.
      6. Mandibulate vs. haustellate
         1. Hemiptera and Homoptera.
         2. Diptera: Culicidae.
         3. Diptera: Tabanidae.
         4. Odonata nymph.
4. Thorax.
   1. Made up of 3 segments; pro-, meso, meta-.
   2. Each has tergum (notum), sternum, pleuron, phragmata between.
   3. Each has pair of legs, wings on last two in pterygotes.
   4. Sutures and sclerites.
      1. Notum (scutum, scutellum, postnotum).
      2. Pleuron (episternum, epimeron); often with other divisions.
      3. Floating sclerites; basalar, subalar, trochantin.
      4. Processes; pleural wing process, anterior notal wing process, posterior notal wing process, pleural coxal process.
      5. Sutures; pleural sulcus or suture, pleuralsternal suture.
      6. Spiracle.
   5. Legs.
      1. Coxa(e).
      2. Trochanter.
      3. Femur.
      4. Tibia.
      5. Tarsus (tarsi); tarsomeres; tarsal claws; pretarsus (arolium).
      6. Can be modified for walking, jumping, swimming, digging, grasping (raptorial), grooming, stridulation.
   6. Wings.
      1. Main veins; costa, subcosta, radius, median, cubitus, postcubitus, anal.
      2. Main crossveins; humeral, radial, r-m, m-cu.
      3. Cells; named after vein in front, discal cell.
      4. Vannal and jugal lobes in hind wing.
5. Abdomen.
   1. Basically 11 segmented plus telson with the anus.
   2. Each has tergum and sternum.
   3. Each with spiracle.
   4. Appendages; seg. 11 often only dorsal epiproct and lateral paraprocts, cerci from segment 10 or 11 (mainly in apterygotes and hemimetabola).
   5. Genitalia.
      1. Female; opening on seg. 8 or 9, often includes ovipositor.
      2. Male; opening on seg 9, may include various structure including commonly claspers.

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