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Honeybees and the nectar of Echium plantagineum L. in southeastern Australia
Author(s) -
CORBET SARAH A.,
DELFOSSE ERNEST S.
Publication year - 1984
Publication title -
australian journal of ecology
Language(s) - English
Resource type - Journals
eISSN - 1442-9993
pISSN - 0307-692X
DOI - 10.1111/j.1442-9993.1984.tb01351.x
Subject(s) - nectar , sugar , pollen , biology , botany , relative humidity , horticulture , sucrose , zoology , food science , meteorology , physics
An account is given of the flower of Echium plantagineum in south‐eastern Australia, including stages and timing of flowering, behaviour of raindrops in the flower and aspects of floral microclimate. The concentration of nectar solutes varied with time and site, with means varying from 2 to 62% (as g sucrose/100 g solution). There was a significant negative correlation between nectar solute concentration and ambient relative humidity: the drier the air, the more concentrated the nectar. Rates of nectar secretion per flower varied with the bagging method, with long‐term bagging reducing net secretion rates, possibly because of re‐absorption. Rates varied with time, day and site, with a temporal pattern of change suggesting a link between rates of photosynthesis and secretion. Maximum nectar secretion rates in short‐term bagging experiments were ca. 300 μg sugar/flower/hr (equivalent to > 2 mglflower/24 hr). Secretion rate was correlated with flower density. As flower density increased, secretion rate per flower decreased; rate of sugar production per unit area increased relatively more slowly than flower density. E. plantagineum could produce > 500 mg sugar/m 2 /day.Honeybees foraged on E. plantagineum only at ambient air temperatures above ca. 17°C unless irradiance exceeded ca. 750 W m ‐2 . Foragers collected nectar or pollen alone, or both, with the type of visit significantly correlated with nectar solute concentration. Below 35% (as g sucrose/100 g solution) most bees took pollen only; above 40%, most took nectar. Mean standing crop of nectar was generally < 100 μg/flower when most bees were taking nectar, but could exceed 1000 μg/flower when bees were absent or foraging mainly for pollen. Honeybees did not always remove all nectar from flowers they probed. Reabsorption of residual nectar may augment the following day's secretion.