1. The working principles, design and operation of an apparatus for keeping aphids in free flight are described. It consists of a large black-walled chamber with a battery of lights above a central opening in the roof and a fan blowing air down past them into the chamber. The aphid flies up toward the lights and is held at a small, fixed distance from them by adjusting the downward air speed to balance the aphid's rate of climb, which can thus be recorded continuously.
2. The uninterrupted first flight of virginoparous Aphis fabae in this chamber comprises a brief erratic opening phase, a long ‘cruising’ phase during which the rate of climb declines, and a final brief erratic phase when it falls to zero and the aphid flies away from the lights. Contact with a non-host surface will then restore the previous behaviour and a number of flights, similar but of decreasing duration, ensue until exhaustion at ½-4 hr.
3. During one flight and over a series of flights there are changes in the aphid's responsiveness to the main lights and to light reflected from the chamber walls or from small objects such as leaves presented in the chamber. There appears to be an optimal (‘preferred’) light intensity for the positive phototaxis, which starts high but declines as the photokinesis (locomotor excitation, measured by the rate of climb) declines, until near exhaustion when the phototaxis becomes negative even to the lowest intensities.