Hi Randy
>However, I also find it surprising, since bumblebees don't store pollen
>and honey to the extent that honey bees do, but the apparent negative
>effects happened long after the exposure!
A possible explanation for this is that the the adults raised from the brood exposed to pesticide are damaged and unable to perform as well as unaffected bees. The lack of vigour of the colony could then affect queen production.
Going back to 2003 Morandin and Winston presented data for Bombus impatiens that look similar. They chose to interpret the lack of statistical significance (for the production of queens of Bombus impatiens) as meaning that there was no effect, but the data presented show trends remarkably similar to those presented by Whitehorn et al yesterday for queen production in Bombus terrestris.
http://www.bioone.org/doi/abs/10.1603/0046-225X-32.3.555
Bear in mind that the Whitehorn study used 6ppb imidacloprid and Morandin and Winston used 7ppb. These values may be a little on the high side - but still conceiveable values for real-life field situations.
best wishes
Gavin
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