DESAI, Sheetal; RAGUSO, Robert A.: Flower morphology, learning ability and nectar discovery time by na�ve Manduca sexta.

The energetic demands of hovering flight require many hawkmoths (Lepidoptera; Sphingidae) to forage for energy-rich floral nectars. Hawkmoths feed from a wide variety of flowers, and plants expend significant energy to compete for their attention as pollinators. If nectar limits a hawkmoth’s fitness, it should favor flowers from which it can maximize energetic gain per unit time. Optimal foraging theory suggests that a key component of this process is the time required for a moth to discover the location of nectar. We designed three experiments to explore the effects of flower morphology and hawkmoth learning ability on nectar discovery time, using a lab colony of Manduca sexta. Na�ve moths were exposed to flowers and discovery times were plotted in “learning curves” over at least 30 visits. First, we asked whether certain sensory cues help moths find nectar more quickly, by manipulating scented paper flowers with nectar rewards. Discovery times were shorter on folded flowers than on flat ones, when the fold led only to the nectary. Stripes radiating from the nectary did not significantly reduce discovery time. However, all paper flowers were less attractive than natural flowers. Second, we asked whether the handling efficiency of convergent hawkmoth-pollinated flowers might be constrained by their diverse phylogenetic origins. Among plants from 4 different families, discovery times were lowest on upright funnel flowers of Datura discolor and highest on nodding, bilateral honeysuckle flowers (Lonicera japonica). Third, we asked whether divergent floral evolution among related tobacco species would alter foraging intensity and discovery time. Flower posture had the highest impact; only flowers positioned 15 degrees or more above the horizon were efficiently handled.