Biology Reference
In-Depth Information
and function, results in early foraging. h e JH could act directly on the
physiology of the bee or indirectly through its ef ect on Vg. h e same
can be said about Vg: it could have JH-independent and dependent ef-
fects. Juvenile hormone is produced in the corpora allata of bees. h ese
are paired secretory glands located on either side of and below the
brain. Gene Robinson's student Joe Sullivan surgically removed the
glands from bees and found that they still initiated foraging at close to
the same age as bees that had not been surgically treated. He thus dem-
onstrated that JH is not necessary for initiation of foraging. h ere must
be a JH-independent pathway or pathways acting.
We also hypothesized that Vg cannot be acting directly on foraging
decisions for pollen, nectar, or water because most Vg is stripped from
the bodies of bees before they initiate foraging, it must instead be prim-
ing the bees for pollen foraging. (However, recent results show that high-
and low-strain foragers do have blood titers of Vg, and high-strain bees
have signii cantly higher levels than low-strain bees, perhaps directly
af ecting foraging behavior [Amdam, Ihle, and Page unpublished data].)
We developed a model that incorporated both the onset of foraging
driven by the double-repressor action of Vg and JH and foraging behav-
ior using Vg as a primer (Figure 7.5). We propose that the onset of for-
aging corresponds to a reduction of blood titers of Vg that reduces the
suppression of JH. JH in turn increases in titer and suppresses produc-
tion of Vg. h is leads to a rapid loss of Vg and the onset of foraging.
However, high-strain bees have more Vg but forage earlier in life.
Where does the Vg go so fast? h e double-repressor model of Gro Am-
dam and Stig Omholt proposes that the blood-circulating titer of Vg is
reduced by feeding larvae, queens, and other workers. Feeding larvae is
the main source of loss. If that is the case, do high-strain bees perhaps
engage in more brood rearing?
h e titer of Vg in a worker rises over the i rst 10 or so days of life. We
proposed that it must reach some threshold level before bees are primed
to forage for pollen. However, it is more likely a continuum than a
threshold because genetic variation exists in populations for Vg titers,
as well as the way the bees load pollen and nectar when they forage.
Some bees load more pollen and less nectar, others more nectar and
