Biology Reference
In-Depth Information
to water and to lower concentrations of sugar than the nectar foragers.
h ey had lower response thresholds. We thought that this might be
because they were more motivated by hunger. Nectar foragers are full
of sugar solution and satiated, while pollen foragers are under nutri-
tional stress from l ying to collect pollen. We fed all bees to satiation
with 30 percent sucrose solution, let them rest for one hour, and then
retested them. Responses to water were no longer dif erent and re-
sponses to sugar solutions were greatly reduced in the satiated bees, but
the dif erences between pollen and nectar foragers persisted. In fact,
the relative dif erences between them increased. Response thresholds
were not i xed; they had been modulated by feeding.
Tanya Pankiw and Keith Waddington kept young bees in cages in
an incubator and fed dif erent concentrations of sugar solution to bees
in the dif erent cages. Bees fed higher concentrations of solution had
higher response thresholds (were less sensitive to sugar) than those fed
lower concentrations. Bees foraging at feeders of dif erent concentra-
tions modulated their response thresholds according to the concentra-
tion of the solutions they collected. As with the bees in cages, those
that foraged on more concentrated solutions were less responsive than
those that foraged on solutions with lower concentrations. h e bees
were collected before they fed at the feeders; this showed that the mod-
ulation of response thresholds was based on their foraging experience,
not on their level of satiation at the feeder. h e i lling of the crop (Fig-
ure 2.8) also had an ef ect on responsiveness, but it was ephemeral.
Bees collecting water arrived at the water feeder with a low response
threshold, but their response thresholds increased as they i lled. Be-
cause water has no nutritive value, their response was, again, a conse-
quence not of nutritional satiation but probably of the mechanical
i lling of the crop.
2.5.3 Response h resholds Change with Experience
Nectar foragers pass their nectar loads to receiver bees when they return
from a foraging trip. (Receiver bees are preforaging-aged bees that re-
