Study Questions    Exam II

1.  Male crickets sing at night to attract females.  Although mating is nocturnal, crickets can also be active during the day especially around sunset.  Crickets are strong fliers and excellent runners and jumpers.  Based on this information, assess the following statements.

a.  The song of male crickets is produced by contracting the flight muscles while disengaging the wing hinge, so that the thoracic sclerites are made to vibrate.

b.  Crickets would possess apposition ommatidia and during the night the pigments of the primary pigment cells would be fully extended to allow for maximum stimulation of the visual pigments, luciferin and trehalose, located in the intima of the scolopophore cells.

c.  The motor programs for flight would be generated by neural subunits called Johnston's Organs located in the protocerbrum.

d.  Running and jumping in the cricket would involve completely separate central pattern generators for moving the hind legs and the main brain and subesophagoel ganglion would not be involved in regulating these two behaviors.

e.  During flight, crickets could assess flight speed using hair plates or the optomotor response, but would use halteres to steer and make adjustments to the wings.

f.  Jumping (a very rapid powerful motion) would involve only slow axons and the cricket would have no means for distributing nervous impulses over large areas and deep into the muscle units of the hindlegs.

2.  While working in your garden one afternoon, you notice caterpillars consuming large amounts of vegetation.  Many of the plants hat they are eating have evolved chemical mechanisms to protect themselves from insect herbivory.  You also notice a colony of aphids and large amounts of sticky liquid on the plant that they occupy.  As you work, you are correctly thinking that:

a.  digestion and absorption in the caterpillars will occur in the foregut, and monosaccharides will be absorbed  in the rectal glands by maintaining a diffusion gradient for glucose across the gut wall.

b.  the apids have a mechanism to eliminate most of the water from the dilute plant sap they they ingest.

c.  some of the plants may produce protease inhibitors.

d.  the muscles for moving the mandibles of the caterpillars contract when they receive an impulse from a motor neuron that releases the neurotransmitter, GABA, which causes the sarcolemma to hyperpolarize, which cause the nucleus of the muscle fiber to release K+ which activates tropomyosin.

Answers:

1.  a.  False:  crickets have a specifially evolved mechanism for sound production, which consists of a file on one wing that is drug across a scraper on the other wing, producing a sound.  This process is called stridulation.

    b.  False:  because crickets are nocturnal/crepuscular they would possess superposition ommatidia.  At night the pigments in the secondary (not primary) pigment cells would be full contracted (not extended) to allow for maximum scattering of light among adjacent ommatidia, to stimulate the visual pigments, rhodoposin and metarhodopsin, located in the rhabdome of the retinular cells.  Luciferin is used in bioluminescence and trehalose is made from glucose and fructuose by the fat bodies. Neither have anything to do with vision. The intima is the cuticular lining of the fore and hind gut and scolopophore cells are components of chordonotal organs; not part of ommatidia.

    c.  False:  motor program would be produced by neural subunits called central pattern generators located in the throacic ganglia (not protocerebrum).  Johnston's organ is located in pedicel of antennae and is a sensory device used for hearing, mechanoreception, etc; is not involved in generating motor programs.

    d.  False:  each hind leg is governed by a separate CPG which can be linked together in different combinations depending upon feedback.  Thus, when walking the CPGs fire alternately, whereas in jumping they fire synchronously.  How the CPGs are combined is regulated by main brain, which inhibits the motor programs, while the subesophagoel ganglion excites the CPGs.  Depending upon the stimulation received by the main brain, certain pathways are disinhibited by the main brain, which allows the subesophagoel ganglion to excite certain pathways, thereby triggering a specfic combination of CPGs and thus a particular movement.

    e.  True and False:  crickets could use hair plates on face or optomotor response to assess flight speed.  Hairs in hair plate bend with wind and the faster the flight the more bending.  Optomotor response measures rate with which background passes over retina and can be used to measure speed.  However, crickets would not use halteres to steer and make adjustments during flight.  These are found only in Order Diptera.  Crickets would use chordonotal organs and campaniform sensilla in wing hinge and wing base to make adjustments during flight.

    f.  False:  each muscle unit of insects is innervated by three axons:  fast (produced rapid, powerful contractions), slow (slower, graded contractions) and inhibitory.  Jumping would involve a fast axon.  To distributed nervous impulse throughout muscle unit, cricket would use Transverse Tubular system (deep invaginations of sarcolemma to distribute impulses deep into muscle) and polyeuronal innervation (multiply branched end of axon to spread synapse over large areas of muscle).

2.  a.  False:  digestion and absorption occur in midgut (fore- and hindgut are lined with intima which prevenets digestion or absorption).  Monosacchrides would be absorbed across midgut epithelium (rectal glands are in hindgut and associated with water balance).  A diffusion gradient would be maintained across midgut epithelium by converting glucose to trehalose in fat bodies, thereby keeping concentration of glucose in hemolymph low.

    b.  True:  have a filter chamber in the esophagus which rapidly removes water from ingested sap to concetrated nutrients.  The removed water is shunted into the hemolymph and then removed by malpighian tubules and dumped into hindgut.  Thus, the midgut is bypassed.

    c.  True:  many plants that are eaten by insects have evolved protease inhibitors, which inhibit protein-digesting enzymes and thus can disrupt the insect's digestion.  However, many insects (and maybe the caterpillars) have evolved ways to deactivate or rapidly eliminate the protease inhibitors so they cause no harm to the insect.

    d.  False:  movement of moutparts would involve excitatory synapses onto muscles, which involves motor neurons that release L-glutamate (GABA is released by inhibitory neurons and causes sarcolemma to hyperpolarize).  L-glutamate causes sarcolemma to depolarize (not hyperpolarize) which would cause the sarcoplasmic reticulum (not nucleus) to release Ca++ (not K+), which would activate troponin, which would bind with tropomyosin and remove it from the actin receptor sites.