This is interesting, but one would think that impact on brood rearing would
be easy to spot, if it was a common outcome resulting from pesticide
exposure at low levels. I'm not aware of any such negative impact being
noted by... anyone... anywhere... ever.

http://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0156886

"Here we describe a role of non-neuronal acetylcholine (ACh) for breeding of
Apis mellifera carnica and a so far unknown effect of neonicotinoids on
non-target insects. Royal jelly or larval food are produced by the
hypopharyngeal gland of nursing bees and contain unusually high ACh
concentrations (4-8 mM). ACh is extremely well conserved in royal jelly or
brood food because of the acidic pH of 4.0. This condition protects ACh from
degradation thus ensuring delivery of intact ACh to larvae. Raising the pH
to ?5.5 and applying cholinesterase reduced the content of ACh substantially
(by 75-90%) in larval food. When this manipulated brood was tested in
artificial larval breeding experiments, the survival rate was higher with
food supplemented by 100% with ACh (6 mM) than with food not supplemented
with ACh. ACh release from the hypopharyngeal gland and its content in brood
food declined by 80%, when honeybee colonies were exposed for 4 weeks to
high concentrations of the neonicotinoids clothianidin (100 parts per
billion [ppb]) or thiacloprid (8,800 ppb). Under these conditions the
secretory cells of the gland were markedly damaged and brood development was
severely compromised. Even field-relevant low concentrations of thiacloprid
(200 ppb) or clothianidin (1 and 10 ppb) reduced ACh level in the brood food
and showed initial adverse effects on brood development."

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