COLLABORATIVE RESEARCH: DETECTION, PERCEPTION AND USE OF FLORAL CO2 IN NECTAR FEEDING BY MANDUCA SEXTA John G. Hildebrand and Robert A. Raguso University of Arizona and University of South Carolina
Many insects are sensitive to environmental carbon dioxide (CO2), and it is known to be important for attraction of blood-feeding species to their hosts, but the behavioral significance of CO2 for insects that feed on floral nectar is largely unclear. Preliminary studies yielded findings suggesting that the hawkmoth Manduca sexta (Lepidoptera: Sphingidae) may use elevated CO2, emitted by newly opened flowers, to help it find unexploited nectar sources during foraging. The principal goal of the proposed research is to confirm and establish the roles of floral CO2 in moths' foraging behavior, and hence pollination of flowers, by investigating ecological, behavioral, and neurophysiological aspects of the sensory detection of CO2 in Manduca. In particular, the project aims to discover: (1) the relationship between a flower's nectar content and CO2 concentration in front of the flower, both before and after a moth's visit; (2) whether and how Manduca uses floral CO2 during foraging; and (3) how sensory information about CO2 is processed and integrated with information about floral scent in the moth's brain. The investigation of foraging behavior in aim (2) addresses, in separate experiments, whether moths evaluate profitable individual flowers or plant patches, and whether foraging moths use sensory information about floral CO2 to increase their nectar intake. We also will test whether moths use floral CO2 alone or in conjunction with floral odor. To achieve these aims, we will use a combination of experimental approaches. We will measure behavioral responses of individual moths, both in the laboratory (for experiments on flying moths in a tunnel and in a climate-controlled flight arena) and in the field (in outdoor flight enclosures), to artificial and natural flowers that vary in the amounts of nectar, CO2, and floral scent that they emit. We will use the techniques of sensory neurophysiology to record responses of nerve cells in the olfactory center of the moth's brain, when the moths are stimulated with CO2 and floral-scent compounds, both separately and together. This approach should yield insights about the adaptive responses of foraging moths to floral stimuli and their underlying neurobiological mechanisms. Among its broader impacts, this research is expected to be useful to the agricultural community, as many moths and other plant-associated insects are beneficial pollinators and/or economically important pests. Manipulation of insect performance via CO2 cues is already used to control blood-feeding insects such as mosquitoes and, on the basis of this research, may be developed similarly to help control moths in an agricultural context. This work may also help to assess the consequences for ecological interactions (food webs, mutualisms) if ambient levels of CO2 continue to increase, as is predicted for global climate change. Importantly, moreover, participants in the project will profit from its multidisciplinary approach and gain experience with a range of methods and technical challenges. Involvement of two undergraduate students is planned. Both collaborating laboratories have records of supporting and training minority students and will continue to do so. The undergraduate student in the South Carolina laboratory will be chosen from the state-wide SC Alliance for Minority Participation in Research (SCAMP) and will visit Tucson each year to meet with project participants and participate in outreach activities. Research findings will be disseminated in written and oral form at scientific conferences and through institutions targeting the public, e.g. the Arizona-Sonora Desert Museum.
