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Topic 5. Sensory systems.

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(Name)

I. MATERIALS.

Noctuid moths. Preserved material is acceptable, but will be destroyed.

Crickets or grasshoppers, any species.

Mosquito, any species.

American cockroach. Preserved material is acceptable, but will be destroyed.

Microscopes and lamps.

Microscope with an eyepiece micrometer, and 100X magnification capability.

Forceps to remove scales for better viewing.

II. LEARNING OBJECTIVES.

Each student should be able to

1. Identify various sensory organs in insects.

How:

Locate tympanal organs in the nocturnal moths and grasshoppers.

Identify Johnston's Organs in mosquitoes.

Identify the cercal nerves in the cockroach and the cercal sensory hairs.

Examine the compound eyes of insects and the ocelli.

III. INTRODUCTION.

Some of the best known sensory structures on insects are present in discrete structures visible on the external body. Compound eyes, and tympanal organs or good examples of these. The function of the compound eyes is vision, but they are specialized to see color, something not appreciated on casual observation.

The tympanal organs are used for sound detection, and insects have evolved special receptors to detect the sonar clicks produced by bats. Obviously these tympanums are important for escape behavior in night flying insects.

Chordotonal organs are important for sound detection, such as female flight sounds produced by female mosquitoes, or air movement such as the famous cercal hair receptors on the cerci of cockroaches.

IV. DIRECTIONS.

Obtain preserved and fresh material from the TA. Look at the conspicuous compound eyes with the aid of a microscope. Care should be taken in examining them otherwise the inconspicuous hairs between the facets might be overlooked. The ocelli are also inconspicuous on the top of the head, and can best be seen in grasshoppers. Try to measure the size of the facet of the grasshopper and a cyclorrhaphan fly. This will require a special eyepiece micrometer. Notice that the facets occur in very regular rows.

If you have access to a water boatman, examine the top and bottom parts of the compound eye. Describe the difference, if any:

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The tympanal organs are either obvious or also inconspicuous. On many noctuid moths, they can be found only after removing the scales covering the thorax or front of the abdomen, then are seen as a thin cuticle sheet stretched over an opening in the cuticle. The tympanum organs on the legs of crickets and grasshoppers are less conspicuous. Examine the front legs near the top of the tibia. Draw the external appearance of the structure seen with the aid of a dissecting microscope. Be sure to include the name of the insect from which the drawing is taken.

V. SUMMARY ANALYSIS.

Describe what you learned from this exercise.

VI. REFERENCES

Gillott, C. 1995. Entomology, 2nd edn., Plenum Press, New York, NY. See Chapter 12, Sensory Systems.

Evans, H. E. 1984. Insect Biology. Addison-Wesley, Reading, MA. See: The sensory system, pp. 145-157, in Chapter Six by G. M. Happ and G. C. Eickwort.

Topic 5. Addendum

Please draw each organ listed on the left after observing through microscopes and name the insects.

Pheromone glands (Insect: )

Tympanal organs (Insect: )

Johnston’s organ (Insect: )

Cercal sensory hairs (Insect: )

Ocelli and Compound eyes (Insect: )

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(Name)

Topic 6