communication

University of Michigan Biological Station

Biology 442 - Biology of Insects

Lecture Notes - Sensory Receptors, Mechanical and Chemical Communication

Mechanical communication.
1. Trichoid sensillae.
  1. Detect touch, sound, air movement, proprioception.
  2. Basic structure - trichogen cell (produces seta), tormogen cell (produces socket), neuron with dendrite in hair and axon to nerve, scolopale (from cuticle).
  3. May detect movement of hair in any direction or only in some directions.
  4. Found over whole body in different insects.
2. Campaniform sensillae.
  1. Detect cuticular stress for proprioception.
  2. Basic structure - lamella (thin section of cuticle), neuron, scolopale.
  3. Neuron is stimulated when dome is deformed upward, so when weight or compression is applied.
  4. Located on parts of the body subject to stress including wing bases and legs.
3. Scolopophorous or Chordotonal organs.
  1. Detect vibrations.
  2. Basic structure - cap cell, enveloping cell, neuron, scolopale.
  3. Usually occur in groups of scolopidia.
  4. Occur throughout body but at least three specialized types. Not visible externally.
    1. Subgenual organ - in proximal part of tibia, detect substrate vibrations and some airborne sounds. May have 10 to 40 scolopidia.
    2. Johnston's organ - in second segment of antennae, best developed in Culicidae and Chironomidae. Perceives movements of antennal flagellum and may detect flight speed, or sound (male mosquitos find females this way), or gravity/orientation, or water surface echolocation.
    3. Tympanal organs - consists of thin cuticle on top of air space (usually an enlarged tracheal sac) with scolopidia. Membrane vibrates when particular frequency is hit and nerve detects movement. Because of this there is only a limited or no response to pitch. Present on prolegs of Gryllids and Tettigoniids, mesothorax of some Hemiptera (Corixa, Plea), metathorax of Noctuoidea, abdomen of Acrididae, Cicadidae, Pyraloidea, Geometroidea.
4. Sound communication.
  1. Sounds as a byproduct of other activity. Wing movement or feeding, e.g. No obvious significance.
  2. Banging the body against the substrate. Death watch beetles and grasshoppers may be for mate attraction. Termites when outside disturbance.
  3. Stridulation - rubbing 2 body parts together. Scraper and file.
    1. Gryllidae, Tettigoniidae - rub wings together for several purposes; mate attraction, aggression, courtship. May sing alternately. Gryllotalpidae also build resonating chamber - can be heard up to 350m away.
    2. Acrididae - femur against wing for similar purposes.
    3. Many others in Hemiptera (often wing base against thorax or beak against prosternum), Coleoptera (neck against pronotum, elytra and femur, some larvae also), Lepidoptera (wings veins, wing against hind leg, sometimes in pupae or larvae for anti-predation or communication with ants).
  4. Tymballing - best developed in Cicadidae. Sound produced as membrane pops in and out. Often more than one pop per nervous impulse because of myogenic contraction. Often see chorusing. Species may be separated by time of singing. Some moths tymbal and may jam bats echolocation system.
  5. Crepitating - Banging wings together. Occurs mainly in Acrididae. Some butterflies may use as startle response.
  6. Forced air - Some Sphingidae whistle by taking in air through proboscis and forcibly expelling. Hissing cockroaches do this out spiracles.
  7. Functions of sounds.
    1. Aggregation - cicadas.
    2. Calling - crickets and others.
    3. Courtship - crickets and others.
    4. Copulatory - Acrididae.
    5. Post-copulatory.
    6. Aggression - Crickets and others.
    7. Alarm - beetle stridulation.
    8. Social - nest mate recognition and food finding in ants and honey bees.
Chemical communication.
1. Basiconic pegs.
  1. Function in olfaction.
  2. Trichogen cell, tormogen cell, several nerve cells, dendrites to surface (often very specific), scolopale.
  3. Tip of dendrite may have liquid surface to receive chemicals.
  4. Most common on antennae.
2. Coeloconic pegs.
  1. Function in olfaction.
  2. Trichogen and tormogen cells, 3 or 4 neurons, dendrites through scolopale open onto cavity on a peg or pegs.
  3. Found on antennae, mandibles, labial palps.
  4. Generally follow odors by turning into wind when detected and drifting downwind otherwise.
3. Trichoid sensillae.
  1. Function in contact chemoreception.
  2. Trichogen and tormogen cells, several neurons (often one for mechanical), dendrites through scolopale to tip of hair.
  3. Common on tarsi, associated with spines to break surface of leaf. Also on mouthparts and ovipositors.
  4. Often one neuron responds to sugar, one to salt, one to water, one may be specialized.
4. Use of Chemicals in Communication.
  1. Hormones internal.
  2. Pheromones external. Intraspecific communication.
    1. Primers - produce long term physiological or developmental effect. Important in social insects in determining castes, also cause grouping in gregarious acridids.
    2. Releasers - immediate effect.
      1. Sex attractants (many insects - especially moths, bark beetles).
      2. Alarm pheromones (aphids, social insects - ants made up of 3 components, exciter, attracter, biting).
      3. Recruitment pheromones (social insects).
      4. Host marking (often in parasitoids or also in things with discreet resources).
  3. Allomones. Interspecific, benefit sender. Usually are defensive secretions such as irritants (Hemiptera, Coleoptera, secondary chemicals in plants and butterflies, flower odors, bark beetle pheromone repels other species of bark beetles).
  4. Karimones. Interspecific, benfit receiver. Usually function in prey or host location. Include plant secondary compounds, host recognition by parasitoids, bark beetle pheromone attracts parasitoids.

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