How does a diurnal hawkmoth find nectar? Differences in sensory control with a nocturnal relative

Recent research shows that a nocturnal hawkmoth, Manduca sexta, inspects flowers in search for nectar by means of a series of hovering and proboscis movements controlled by different sensory modalities, mainly vision and mechanoreception. The diurnal Macroglossum stellatarum is a closely related hawkmoth challenged with the same task but under illuminances 6--8 orders of magnitude higher. Here, we use flower models presenting color markings, 3D features, or both to study innate flower movements and sensory cues involved in the innate inspection behavior of M. stellatarum. On flat plain colored models, moths scanned the whole corolla with their proboscis, attaining intermediate success levels. When models presented color markings, moths biased proboscis placement, which affected inspection efficiency. Three-dimensional features affected inspection behavior and efficiency, by provoking strong "diving" responses. When both visual and tactile features were present, visual cues showed prevalence in the control of the inspection behavior. We evaluated learning abilities of moths, finding that M. stellatarum cannot only improve their efficiency by calibrating innate responses but also by changing their innate strategy. We discuss results on flower inspection behavior of M. stellatarum comparatively with known aspects of this behavior in M. sexta. Motor responses appear to be shared by these hawkmoths, but their sensory control shows important differences. Future studies will evaluate whether these differences are the result of an evolutionary divergence of their innate behavior associated with a switch to diurnal activity or the result of a flexible use of sensory information by the naïve animals. Copyright 2011, Oxford University Press.