The phototactic responses of several species of triatomid bug have been investigated in the context of published information on the use of light traps as a means of collacting insects. A review of the literature indicates a considerable lack of suitable trapping methods for triatomids and so it is significant that these nocturnal insects are attracted to light. More specifically, all instars of the triatomic species studied here have manifested a distinct attraction to a comparatively new light source called betalight. Betalights consist essentially of sealed glass vessels filled with tritium. The contained tritium emits beta-particles which strike an internal coating of phosphor, this in turn producing a continuous subdued light. Betalight is a completely self-powered light source and may provide a useful attractant for triatomids in the field. The laboratory investigation presented here was therefore concerned with elucidating those factors, both physiological and environmental, likely to influence the relative attractiveness of a betalight source. Photoperiodic entrainment has significance in determining the timing of the triatomids' general locomotor activity and concomitantly, their dial pattern of phototactic behaviour. The spectral composition and brightness of the betalight may be important in so far as betalights in the higher microlambert range, emitting shorter wavelengths of radiation, elicit significantly greater responses. The bug's levels of metabolic reserves also appear to govern the pattern of phototactic behaviour. In this connection, an investigation of the physiological significance of ecdysis, post-emergence biology and nutritional history yielded particularly valuable findings. Of the environmental factors, ambient temperature has particular relevance. Considerably enhanced responses to betalight are elicited at more elevated temperatures. It is suggested that the level of response may be correlated with the bug's locomotor velocity, the latter bearing a linear relationship to environmental temperature.