Anyone who has tried to swat a house y can appreciate the agility in ight e xhibited by these creatures. Unlike ying insects having two pairs of wings (dragon ies, moths, butter ies, etc.), dipteran ies have one pair of wings and short, stubby bodies. That they can y in a controlled, purposeful manner must be considered remarkable. What is even more fantastic is the fact that ies use dynamic visual information along with inertial information to stabilize their ight. The inertia information for ight stabilization of dipteran ies comes from a unique pair of vibrating gyroscopes (angular rate sensors), which have evolved over the millennia from the hind wings. These dumbell-shaped organs, called halteres, reside on the sides on the y in back of the wings, and are vibrated at wing-beat frequenc y by modi ed ight muscles. Each haltere swings through an arc of nearly 180° (Schwartzkopff, 1964). Figure 2.7-1 shows a haltere on the left side of a (dipteran) mosquito.
Where the halteres attach to the y's body there are many mechanoreceptor cells (campaniform sensillae) whose presumed function is to respond to the vibrating, gyroscopically induced torques on the halteres produced when the y under goes a rotational departure from level straight ight (roll, pitch, or yaw) (Bullock and Horridge, 1965). More particularly, the haltere system can theoretically respond to roll, pitch, and yaw rates to provide high-speed feedback to the wing ight muscles to stabilize ight. The bases of Dipteran halteres are endowed with a profusion of chordotonal organs and campaniform sensilla mechanoreceptors that presumably respond to the dynamic forces and torques on the haltere support as the insect undergoes roll, pitch, and yaw in its ight. The outputs from these sensory neurons at the base of the halteres is evidently integrated with visual information from the compound eyes to give complete ight control. A good illustration of haltere mech-anosensors can be found in Figure 20.9 in Bullock and Horridge (1965).
The next section derives expressions for the torques produced at the base of a model haltere when it is subject to angular velocity in certain planes.
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