Biology Reference
In-Depth Information
nectars appears to be a physiological necessity for large bees at low or mod-
erate ambient temperatures, because their very high metabolic water produc-
tion during flight far exceeds evaporative water losses (Nicolson & Louw,
1982; Bertsch, 1984).
Like moths and butterflies, honeybees
have been shown to prefer sucrose
to fructose and fructose to glucose (Waller, 1972; Bachman & Waller,
1977). However, the use of artificial flowers of different colours in tests of
honeybee sugar preference leads to different results, because the constancy
of individual bees to either blue or yellow “flowers” can override sugar pref-
erences (Wells et al., 1992). Kearns and Inouye (1993) have discussed the
relative merits of different feeder types in assessing the responses of honey-
bees to sugar solutions: these range from open dishes where large numbers
of bees can feed simultaneously to small volume artificial flowers, which
may or may not be replenished after each visit. By filling the holes of micro-
titre plates with different sugar solutions, Biesmeijer et al. (1999) showed
that stingless bees (
Melipona
sp.) preferred sucrose to glucose and fructose,
though they did not discriminate between hexose-rich and hexose-poor solu-
tions. Bee nectars were separated by Baker and Baker (1983) into high
sucrose nectars favoured by long-tongued bees and low sucrose nectars fa-
voured by short-tongued bees, but this may be due to the slower hydrolysis
of sucrose in deep flowers (Willmer & Stone, 2004). Sucrose hydrolysis is
rapid in a bee's crop (Nicolson & Louw, 1982), the necessary α-glucosidase
being produced in the hypopharyngeal glands rather than in the midgut as in
other nectar feeders (Terra & Ferreira, 1994). The rate of crop emptying de-
pends on sugar concentration, as in other insects, and is adjusted to the
energy demands of the bee (Roces & Blatt, 1999). Passive absorption of
monosaccharides from the midgut is also extremely rapid, with a favourable
gradient aided by the conversion of glucose to trehalose: when hungry hon-
eybees are fed labelled glucose, labelled trehalose can be detected in the
haemolymph only 2 min later (Gmeinbauer & Crailsheim, 1993). Where the
less common nectar sugars are concerned, Barker and Lehner (1974) studied
the survival of honeybees on 13 different sugars, and the consumption of
those sugars during cage experiments.
Like butterflies, honeybees show positive responses to amino acid mixtures
mimicking the amino acid composition of nectar, but negative responses to
individual amino acids when tested at high concentrations (Inouye & Waller,
1984; Alm et al., 1990). Among the amino acids that occur at relatively high
concentrations in nectar, phenylalanine has a strong phagostimulatory effect
on bees (Petanidou et al., 2006); honeybees prefer synthetic nectars rich in
