Why is alsynite fiber glass sheet attractive to stable flies? Optical and behavioural studies

The fiber glass material Alsynite (Sequentia Corporation) is known to be an effective visual attractant to stable flies, Stomoxys calcitrans. The basis for this attractiveness is not certain, but is found to correlate with high near-UV reflectivity. While examining the transmission properties of Alsynite, it was found that the ratio of short- to long-wavelength photons shifts from 0.17 to 0.77, depending on the angle of the Alsynite relative to the source and the detector. This shift occurs suddenly at an angle of 15 degrees from the normal. To the human eye this shift results in an iridescent blue halo appearing around a light source and at the boundaries of illuminated objects. The phototactic response of stable flies to the 15 degrees off-axis spectral condition, as measured behaviourally, is greater than or equal to their phototactic response to a tungsten source more than 20 times the spectrally corrected intensity. This demonstrates a real preference for the off-axis photon ratio and may in part explain why Alsynite is attractive to stable flies in field situations.