Preference for certain types of flowers in bee species may be an adaptation for efficient foraging, and they often prefer flowers whose shape fits their mouthparts. However, it is unclear whether such flowers are truly beneficial for them. We address this issue by experimentally measuring foraging efficiency of bumblebees, the volume of sucrose solution consumed over handling time (µL/second), using long-tongued Bombus diversus Smith and short-tongued B. honshuensis Tkalcu that visit Clematis stans Siebold et Zuccarini. The corolla tube length of C. stans decreases during a flowering period, and male flowers are longer than female flowers. Long- and short-tongued bumblebees frequently visited longer and shorter flowers, respectively. Based on these preferences, we hypothesized that bumblebee foraging efficiency is higher when visiting flowers that show a good morphological fit between the proboscis and the corolla tube. Foraging efficiency of bumblebees was estimated using flowers for which nectar quality and quantity were controlled, in an experimental enclosure. We show that 1) the foraging efficiency of B. diversus was enhanced when visiting younger, longer flowers, and that 2) the foraging efficiency of B. honshuensis was higher when visiting shorter female flowers. This suggests that morphological correspondence between insects and flowers is important for insect foraging efficiency. However, in contradiction to our prediction, 3) short-tongued bumblebees B. honshuensis sucked nectar more efficiently when visiting younger, longer flowers, and 4) there was no significant difference in the foraging efficiency of B. diversus between flower sexes. These results suggest that morphological fit between the proboscis and the corolla tube is not a sole determinant of foraging efficiency. Bumblebees may adjust their sucking behavior in response to available rewards, and competition over rewards between bumblebee species might change visitation patterns in the wild. Thus, the determinants of foraging efficiency and visitation frequency for bee pollinators may be more complex than previously thought.

The interaction between the non-native coccinellid beetle, Curinus coeruleus Mulsant, and the Hawaiian native plant Hibiscus brackenridgei A. Gray, was investigated on Kauai, HI. The presence of extra floral nectar appears to maintain the beetle presence on the plant. Because coccinellid beetles are predators on insects that are damaging to plants, beetle presence may increase plant fitness. Beetles were found feeding heavily on the extra floral nectaries of the Hibiscus. An examination of the beetle mouth parts with scanning electron microscopy revealed no structures specifically adapted for the consumption of nectar. The sensory ability of the coccinellids was tested to determine if they respond to visual or olfactory cues to detect the nectar. Studies with an eight-armed air-flow olfactometer concluded there was no olfactory cue. Tracing the pathways of beetles in laboratory experiments yielded results that suggest a visual cue. The extra floral nectaries are concluded to be a potential mechanism to maintain beetle presence on a plant to provide defense against herbivores.