A Spectral Zone of Color Preference for the Onion Fly, Delia Antiqua (Diptera: Anthomyiidae), With Reference to the Reflective Intensity of Traps

It was hypothesized that Delia antiqua (Meigen), the onion fly, would show high preference in the field for trap colors reflecting visible wavelengths between 400 and 480 nm at reflective intensities above 37%. This preferred spectral zone (PSZ) was tested in an onion field in 1984, using cardboard traps painted with 11 blue, violet, and green hues, and two PSZ reflecting colors of varying intensity. It was found that colors with peak reflective wavelengths occurring between 400 and 470 nm, at or above 30% reflectance intensity, were most preferred. Wavelength-specific reflectance intensity was shown for the first time under field conditions to influence the magnitude of color preference in the onion fly.