Biology Reference
In-Depth Information
nectar loads entering a single colony over a 5-day period. Honeybees are
very sensitive to differences in nectar concentration. In the same study,
Seeley (1986)
recorded a 30% drop in recruitment rate for a decrease of only
0.125 M (4%) in concentration (Fig. 3). The relationship between the dance
rate of bees and sugar concentration is likewise non-linear, with a more pro-
nounced change at low concentrations: bumblebees foraging at small-volume
artificial flowers in the laboratory prefer 20% over 10% sucrose solutions
more strongly than they prefer 50% over 40% (Waddington, 2001). The re-
sponse of bees to a particular nectar concentration depends very much on the
ecological context, which is an important consideration in studies involving
feeder choices in a natural environment. In one of his classic papers, Lindauer
(1948) showed that the threshold sucrose concentration for eliciting recruit-
ment behaviour in honeybees declined from 2 M (~55% w/w) during the
main nectar flow in spring to around 0.1 M (3.5%) in mid-summer, when
bee forage became scarce and competition was intense.
The thoracic temperatures and metabolic rate of honeybees vary with
both the reward rate at the food source and the motivational state of the bees.
Dandelion foragers have been recorded as 10
o
C warmer than bees visiting
sunflowers (Kovac & Schmaranzer, 1996). Graduated thermal behaviour
occurs during food unloading in the hive, as well as at feeding locations. It
has been shown that the temperature of dancing bees recruiting their nest-
mates increases with food quality and the number of brood cells, and
decreases with distance of the food source from the hive and the amount of
stored honey (Stabentheiner, 2001). The increased thoracic temperature of
the receiver bees in turn raises their activity level, ensuring that nectar from
more profitable sources is processed faster (Farina & Wainselboim, 2001).
Stingless bees (
Melipona panamica
) have also been shown to regulate their
thoracic temperature according to food concentration and distance from the
nest, with distance having a much greater effect (Nieh & Sánchez, 2005).
As individuals, flying honeybees are in negative water balance at ambient
temperatures above 31
o
C unless they collect either dilute nectar or water
(Roberts & Harrison, 1999). When it is necessary to cool the hive by evapora-
tion, bees will collect water or dilute nectar (Ohguchi & Aoki 83). Most desert
bees are solitary and must acquire water from nectar (Willmer & Stone, 1997).
In Israel, foraging choices of the mason bee
Chalicodoma sicula
are dictated
by its water needs, and field measurements of its blood osmolality show rapid
corrections after the ingestion of nectar of
Lotus creticus
(Willmer, 1986).
Two carpenter bees (
Xylocopa
), also in Israel, depend on the water compo-
nent of nectar of
Calotropis procera
(Apocynaceae), especially the smaller
of the two species because it generates less metabolic water (Willmer, 1988).
