Ultraviolet and violet light: attractive orientation cues for the Indian meal moth, Plodia interpunctella

The Indian meal moth (IMM), Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), engages in long-distance or foraging flights in the twilight hours of the scotophase when blue light dominates the irradiance spectrum of the sky. We tested the hypothesis that IMM uses wavelengths of visible blue/violet light as orientation cues that trigger phototactic responses. In four-choice laboratory experiments, blue light (400–475 nm) was significantly more effective than green (475–600 nm), orange (575–700 nm), or red (590–800 nm) light in attracting males and mated females. In subsequent experiments that tested light emitting diodes (LEDs) emitting peak wavelengths in the blue/violet-light range, the 405-nm 'violet' LED was significantly more effective than the 435-, 450-, or 470-nm 'blue' LED in attracting males as well as virgin and mated females. In electroretinogram recordings, the 405-nm wavelength elicited significantly stronger receptor potentials from female and male eyes than the 350-nm (UV) wavelength, and in a behavioral experiment it significantly enhanced the known attractiveness of UV light. Equal attraction of IMMs to 405-nm LEDs at 600–700 µW/cm² with or without UV light, and significantly stronger attraction to a 405-nm LED than to a 350-nm LED at maximum light intensities, suggest that the deployment of violet instead of UV light could become one of several management tactics for control of IMMs.