Photostimulus intensity, rather than colour or polarization, is the key driver for stable fly visual attraction in laboratory bioassays

Research has shown that stable flies, such as Stomoxys calcitrans, are attracted to certain visual cues when foraging for hosts. These cues include relative intensity, spectral composition, and the angle and degree of polarization. To understand the role of each of these visual cues, researchers conducted laboratory two-choice bioassays.

In these experiments, female or male stable flies were offered a choice between paired stimuli that differed in their visual characteristics. The flies were recorded landing on the stimuli, with landing responses serving as the response criterion. The results revealed that stable flies consistently preferred lower-intensity visual stimuli, even when the stimuli varied greatly in spectral composition and polarization.

Interestingly, when paired stimuli had the same relative intensity, the flies were unable to distinguish between a stimulus presenting ultraviolet, blue, green, and red wavebands and a corresponding stimulus lacking one of these wavebands. These findings support the hypothesis that stable flies may respond to color and polarization characteristics of visual stimuli as modulations of perceived intensity.

Understanding the mechanisms behind stable fly visual attraction could help in designing more effective vision-based traps to target stable flies and other biting flies.