Wavelength discrimination and the role of ultraviolet vision in the feeding behavior of hawkmoths

Nocturnal Sphingidae are important pollinators in tropical forests. Hawkmoth flowers are typically white to the human eye. As the retinas of hawkmoths contain ultraviolet-sensitive photoreceptors, flower patterns reflecting ultraviolet wavelengths might be significant to sphingid feeding behavior. The flowers of ten hawkmoth-pollinated species were examined with an ultraviolet sensitive video system in Monteverde, Costa Rica. All lacked ultraviolet reflectance. A common hawkmoth species, Manduca sexta, was used in free choice experiments to determine which wavelengths elicited proboscis extension, probing and drinking of sugar water. When offered a choice between artificial flowers or backlighted filters, Manduca strongly preferred to feed at those reflecting or transmitting only wavelengths >400 nm, avoiding those that also included ultraviolet wavelengths. Feeding behavior was thus best elicited by stimuli that mimicked the reflectance of typical hawkmoth flowers. Feeding behavior must be primarily activated by either the green- or violet-sensitive mechanisms (or both) of the hawkmoth visual system, while concurrent activation of the ultraviolet-sensitive mechanism interferes with it. -from Authors