Pollen foraging by bumblebees: Foraging patterns and efficiency on Lupinus polyphyllus

Abstract

Bumblebees foraging on vertical inflorescences start near the bottom and work upward, behavior commonly interpreted as a response to the greater amounts of nectar available in lower flowers. Lupinus polyphyllus, which produces no nectar, has more pollen available in upper flowers. Although bees are probably unable to detect this gradient, since pollen is hidden from their view, they still start low and forage upward. Therefore, we concluded that the bees' tendency to forage upward on vertical inflorescences is not tied to a reward gradient. In addition, bees use only about 15% of the flowers per inflorescence, although they could be much more efficient by visiting and revisiting every flower systematically. In general, revisits would not be penalized because most flowers contain enough pollen for several visits. Optimal foraging theory may not offer an adequate explanation for such gross inefficiency.

Behaviour of pollinator insects within inflorescences of Scrophularia species from Iberian Peninsula

“…Also, the larger amount of nectar produced by these species (25.5–32 μl flower −1 day −1 in large‐flowered species versus 5.8–11.3 μl flower −1 day −1 in medium‐flowered species; Ortega‐Olivencia & Devesa 1993b) could explain why there are fewer vertical displacements, since the pollinators could become satiated through visiting just a few whorls to obtain maximum resources. This higher frequency of horizontal movements was also observed for Bombus foraging on Lupinus polyphyllus (Haynes & Mesler 1984), although these authors proposed the cause as being that the landing platform is horizontal and does not cause the bees to face upwards or downwards.…”

Change of Floral Orientation within an Inflorescence Affects Pollinator Behavior and Pollination Efficiency in a Bee-Pollinated Plant, Corydalis sheareri

“…This is corresponding with the fact that pollinators who forage in a head-down position tend to move downwards on inflorescences [21]. Additionally, the upward movement is also explained by that pollinators may have a better vision above than below when they position themselves upright [20], [37]. The effect of floral orientation on direction of pollinator movement may be attributed to the influences on both foraging posture and the view of pollinators.…”

Discrimination by Pollen-Collecting Bumblebees among Differentially Rewarding Flowers of an Alpine Wildflower, Campanula rotundifolia (Campanulaceae)

“…Nectaring bumblebees are able to select the floral variants that offer larger amounts of nectar, apparently by associating the potential value of the reward with a visual cue (Bell et al 1984, Cresswell andGalen 1991) and many such instances are explicable by reference to simple economic models that derive diets offering the maximum rate of nectar uptake (reviewed in Stephens and Krebs 1986). However, bee-pollinated plants often provide pollen rewards and, despite earlier scepticism (Hodges andMiller 1981, Haynes andMesler 1984), recent studies have demonstrated that bumblebees detect differences in pollen availability as they harvest the pollen and consequently adjust the amount of time spent on a flower or inflorescence (Buchmann andCane 1989, Harder 1990). As yet, no published study has shown pre-alighting (remote) discrimination among floral variants on the basis of differential pollen rewards.…”