Seasonal changes in juvenile hormone titers and rates of biosynthesis in honey bees |
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Authors: | Z -Y Huang G E Robinson |
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Institution: | (1) Department of Entomology, University of Illinois, 61801 Urbana, IL, USA |
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Abstract: | Honey bee colonies can respond to changing environmental conditions by showing plasticity in age related division of labor,
and these responses are associated with changes in juvenile hormone. The shift from nest taks to foraging has been especially
well characterized; foraging is associated with high juvenile hormone titers and high rates of juvenile hormone biosynthesis,
and can be induced prematurely in young bees by juvenile hormone treatment or by a shortage of foragers. However, very few
studies have been conducted that study plasticity in division of labor under naturally occurring changes in the environment.
To gain further insight into how the environment and juvenile hormone influence foraging behavior, we measured juvenile hormone
titers and rates of biosynthesis in workers during times of the year when colony activity in temperate climates is reduced:
late fall, winter, and early spring. Juvenile hormone titers and rates of biosynthesis decreased in foragers in the fall as
foraging diminished and bees became less active. This demonstration of a natural drop in juvenile hormone confirms and extends
previous findings when bees were experimentally induced to revert from foraging to within-hive tasks. In addition, endocrine
changes in foragers in the fall are part of a larger seasonally related phenomenon in which juvenile hormone levels in younger,
pre-foraging bees also decline in the fall and then increase the following spring as colony activity increases. The seasonal
decline in juvenile hormone in foragers was mimicked in summer by placing a honey bee colony in a cold room for 8 days. This
suggests that seasonal changes in juvenile hormone are not related to photoperiod changes, but rather to changes in temperature
and/or colony social structure that in turn influence endocrine and behavioral development. We also found that active foragers
in the late winter and early spring had lower juvenile hormone levels than active foragers in late spring. In light of recent
findings of a possible link between juvenile hormone and neuroanatomical plasticity in the bee brain, these results suggest
that bees can forage with low juvenile hormone, after previous exposure to some threshold level of juvenile hormone leads
to changes in brain structure. |
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Keywords: | Corpora allata Seasonal variation Juvenile hormone Social insects Honey bee Apis mellifera |
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