The interaction of ultraviolet (UV = 350-400 nm) and visible (VISIBLE = 400-650 nm) wavelengths in the visual behaviour of the onion fly, Delia antiqua (Meigen), was examined by measuring spontaneous alightment on various UV-and non-UV-reflecting, sticky cardboard traps in onion fields. Alightment on traps was negatively correlated with the percent UV (350 nm) and green (540-580 nm) reflectance and positively correlated with the percent blue (430-470 nm) reflectance. Alightment varied directly with the ratio of 'stimulatory'/'inhibitory' reflected wavelengths. Males and females were similar in their response to both UV and VISI-BLE wavelength reflectance, with the exception that males were more sensitive than females to UV-reflecting white surfaces. A multiple regression model, that used the intensity of 3 key wavelengths, 350, 450 and 560 nm, as independent variables, explained 90% of the variation in the combined male and female response to spectral reflectance from traps. These results indicate that some visual behaviours of D. antiqua are a function of the integration of sensory input from the entire spectral distribution of the stimulus, and not simply the dominant wavelengths or hue.

Pine oil (Norpine-65, Northwest Petrochemicals) was assessed as an oviposition deterrent for gravid female onion maggots, Delia antiqua (Meigen), in two types of laboratory experiments. When given a choice for 24 h between a control onion half treated with hexane and an onion half treated with pine oil in hexane, the females oviposited preferentially on or around the control onion half. In a no-choice experiment the females laid over three times as many eggs on or around solvent control onions as on or around onions treated with 1.0% pine oil. The DC50 (deterrent concentration50) was calculated to be 0.09%. The results suggest that pine oil (or its constituents) may have potential as an oviposition deterrent under field conditions.