The exploitation of floral nectar in Eucalyptus incrassata by honeyeaters and honeybees

Summary During October and November, 1977, a study of nectar production and nectarivore foraging in Eucalyptus incrassata was conducted at Wyperfeld National Park in south-eastern Australia in order to evaluate the extent to which introduced honeybees (Apis mellifera) compete with native honeyeaters for floral nectar. Data on nectar production, nectar availability, ambient air temperature and the numbers of visiting honeyeaters and honeybees were collected. Most of the daily nectar production in E. incrassata occurs early in the morning when temperatures are too low for insects to forage. In addition, insects, particularly honeybees, are unable to exploit nectar in the youngest flowers because the stamens are clustered tightly around the style. As a result of these temporal and structural characteristics of the flowers, honeyeaters are able to harvest most of the nectar. Honeybees potentially have access to 35–47% of the average daily production of floral nectar in E. incrassata and actually harvest considerably less. These data show that E. incrassata flowers are adapted to restrict insect foragers despite their superficially unspecialized appearance. Eight forest and woodland eucalypts do not have a flower stage which excludes insects and the significance of this difference is discussed.