AN OPTOELECTRONIC SENSOR FOR MONITORING SMALL MOVEMENTS IN INSECTS

Abstract

Optical movement detectors are often used in laboratory studies of insect behavior. They offer advantages of time resolution and ease of analysis compared with video. However, design and construction have rarely been described in enough detail to allow the devices to be built easily by others. We describe a simple optoelectronic system for measuring rapid movements in one dimension, such as the protraction of an insect leg. The leg casts a bar-shaped shadow onto a photodiode chip that is masked to expose a triangular area. Movement of the leg changes the total area of the triangle that is shaded. A preamplifier converts the change in photoelectric current to a voltage signal. The preamplifier includes an optional circuit for removing 120 Hz ripple resulting from AC-powered light sources by subtracting the output of a second, reference photodiode. We have used the system to quantify leg movements in an acoustic startle response of a field cricket (Teleogryllus oceanicus LeGuillou). This system could be adapted for a wide range of other applications in laboratory and field research.