According to the book "Pollinator Protection: A Bee and Pesticide Handbook" recommended to us by Jerry Bromenshenk a few days ago:

"Queens are often superseded or the colony becomes queenless.  This is what we suspect is involved when the brood cycle is broken within a few days of the time the insecticide was applied.  Foragers have probably stopped bringing in pollen.  When there is a lack of pollen, the hive bees will begin feeding on the eggs or there may simply be a lack of clean and/or empty cells for the queen to lay in because foragers are depositing nectar in the brood combs.  The queen often remains alive and apparently healthy for a week or more before she is superseded.  Under normal conditions, healthy workers begin to produce royal jelly (the queen substance precursor) a few days after they emerge.  Lack of brood is not related to supersedure, but the supply of queen substance is, and when it falls below a critical amount the workers will get rid of the queen; the contaminated pollen/queen supercedure syndrome.  When there are no eggs or young larvae present, the workers can no longer rear a new queen and no supersedure cells are present.  Queenlessness has been associated with the use of a wide variety of insecticides, including arsenicals, dieldrin, Sevin, Orthene, malathion, parathion, and Penncap-M.  Typically, severe Sevin dust poisoning makes at least half the colonies queenless within 30 days.  Severely weakened and queenless colonies do not survive the following winter."

Pages 36-37.  Written by Carl Johansen and Daniel Mayer. Published 1990, Wicwas Press.

Date:    Fri, 8 Feb 2013 13:19:35 -0500
From:    allen <[log in to unmask]>
Subject: Sub-Lethal Effects of Pesticides

(The term "pesticides" includes both fungicides and insecticides)

> The effects of sublethal pesticide exposure on queen emergence and
> virus titers were examined.

That reminds me.  What is known about the effects of various pesticides
on queen acceptance and queen supersedure?

Are there known effects of sub-lethal doses on the raising of queens and
the willingness of colonies to start and maintain cells?

I wonder about that because it seems to me that the field tests that
have indicated no apparent harm may have been done on colonies assumed
to be -- or designed to be -- in a steady-state and not on colonies
which were required to raise queens.

Oftentimes, it seems to me, colonies which prove to be unusual are
removed from the study or adjustments are made.

Could they be the more important and interesting part of such studies?

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