Biology Reference
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life. High- and low-strain workers of these cohorts had lived together
in the same hive environment and had not foraged; therefore, their re-
sponses could not be consequences of their foraging experiences. High-
and low-strain bees of all three cohorts dif ered signii cantly in sucrose
sensitivity, with high-strain workers always more sensitive; H1 and H2
were thereby eliminated as plausible explanations. High-strain bees 0 to
2 days old were 100 times more sensitive to sucrose than low-strain bees
of the same age. (We subsequently showed that 4-hour-old high- and
low-strain workers dif er; see Section 5.6). Sensitivity of high-strain
bees did not increase with age. However, sensitivity of low-strain bees
did increase, which suggests that high-strain workers are developmen-
tally more advanced. h is is consistent with their early onset of forag-
ing behavior. High-strain queens and drones are also more sensitive to
sucrose than are queens and drones of the low strain, and they never
forage; this suggests fundamental, genetically variable, neurophysio-
logical dif erences in sensory-response-system tuning between high-
and low-strain bees.
5.4.1.2 High- and Low-Strain Bees and Foraging Loads
Comparisons of
the crop (honey stomach) contents of high- and low-strain foragers
coni rmed our expectations based on the hypothesized relationships
between water responses and sucrose sensitivity and foraging behavior.
A greater proportion of high-strain foragers returned with water and
with lower concentrations of nectar, while a larger proportion of low-
strain bees returned empty. High-strain bees with high responsiveness
to water and high sensitivity to sucrose accepted a broader range of
liquids. Low-strain bees with less sensitivity to sugar accepted only the
higher-quality nectar or returned empty. Collectively, the results of this
study caused us to reject the hypothesis that observed dif erences in
sucrose sensitivity of high- and low-strain workers are simply conse-
quences of foraging experience. Instead, the results support the hy-
pothesis that genotype determines sensitivity to sucrose (and perhaps
foraging behavior independently), that foraging behavior modii es it,
and that the response is set very early in life and correlates with behav-
ior much later (H2 or H6; Figure 5.8).
