Aphid flight-track analysis in three dimensions using video techniques

A technique is described for the three-dimensional analysis of the flight paths of small insects using two video cameras placed alongside each other with the optical axes coincident at a point some distance beyond the area of interest. The video signals were mixed and a time base introduced before recording the superimposed images from both cameras on a single VCR. With suitable lighting and a black background, flying aphids appeared on the monitor as double, bright images on a dark background. The distance between the two images was inversely proportional to the distance of the aphid from the camera lenses. A calibration grid was used to insert the correct parameters into software designed to provide the x (vertical), y (horizontal) and z (distance from the cameras) Cartesian co-ordinates for a flying insect and to calculate the distances flown, flight speed and turning parameters. The advantages of the system are that it is designed for a single VCR and monitor, provides automatic synchrony between camera signals and can examine a larger visual arena than screen-splitting methods. It operates with insects as small as aphids, and wind-tunnel studies on the black bean aphid, Aphis fabae Scop., showed that some flight parameters (for the final one-second approach to a visually attractive landing platform) differed according to whether wind was present or not. Thus, ground speed and distance moved differed significantly but turning parameters were unchanged. In addition, flight trajectory on the approach to landing depended upon initial direction of flight and the presence of wind.