Mate-finding and host localization by nocturnal moths are predominantly mediated by olfactory signals and cues, respectively. Nevertheless, some nocturnal moth species rely on olfactory and visual cues to locate resources, such as flowers. Although traps are indispensable for the detection and monitoring of corn earworm moths, Helicoverpa zea (Boddie), a generalist and highly destructive crop pest, the role of visual cues in locating a pheromone source is poorly understood. Here, we investigated whether trap color influences the trap catch of the corn earworm. We showed that trap design affected male H. zea trap catch, with Hartstack-type traps being more effective than bucket traps, and more H. zea males were trapped in light-colored traps (white, yellow). However, under the dim ambient night conditions, when H. zea males fly, it is unlikely that they can discern trap colors. Instead, it is probable that H. zea males discriminate traps on the basis of their gray-scale reflectance, ranging from white to black. We found a positive correlation between trap captures and the relative luminance of dyed cheesecloth fabrics that we wrapped around Hartstack traps. Our findings suggest that at night, H. zea integrates the visual contrast between the trap and foliage background (ie apparency of the trap) in locating sex pheromone-baited traps.

Graphical Abstract