Age-specific and Sex-specific Nectar and Pollen Use by a Butterfly Pollinator

Age-specific patterns of nectar and pollen use by insect pollinators may reflect behavioral or physiological changes over the insects lifespan, and may also influence flower visitation rate. Studying Heliconius charithonia (Lepidoptera: Nymphalidae) and Psiguria umbrosa (Cucurbitaceae), we showed that honey-water (as a nectar substitute) intake increases over the first ten to twelve days of females life, while decreasing over the same age period for males, when individuals were fed ad libitum. Intake then remains stable at least through 28 days of age. Mean intake is higher for females than for males, and is not significantly affected by body size. Intake patterns for honey-water and pollen did not change with age in a similar manner. Pollen feeding increased significantly with age for both sexes, with females showing a two week delay in the increase when studied in a free-flying greenhouse population with competition for pollen. Under both ad libitum and pollen competition conditions, females collected more pollen than did males. Body size did not significantly affect the amount of pollen collected for either sex. Within each sex, butterflies with ad libitum pollen collected more pollen than those in a free-flying greenhouse population with more restricted pollen availability. These results suggest that two resources obtained from the same source, pollen and nectar, are not treated identically by the insect pollinator, and that the demography of the insect population may affect flower visitation rates in some cases. Further, foraging patterns for pollen and nectar are likely driven by physiological demand for different resource types.