From a soon to be published artice in the Maine State Beekeepers
newsletter:

Imidacloprid, the ingredient in Gaucho, is also in a variety of other
insecticides, including Admire, Cinfidor, and Impower. In the August
2000 issue of HiveLights, an article by Medhat Nasr (who will speak to
the MSBA at the March Annual Meeting) detailed results of tests on
Imidacloprid.
Impower was used as a seedling drench on tomato plants after they grew
their first true leafs. The seedlings were in a greenhouse. Bumblebees
were used in pollination and were introduced less than thirty days after
the introduction of Impower. In two trials, all the greenhouse
bumblebees died. Many were found on the floor, “spinning in circles and
showing tremors”. This resulted in a company that produces bumblebees
for greenhouse pollination to recommend that the bees not be introduced
to the greenhouse within 30 to 45 days after using Imidacloprid.
Nasr also indicated that even though Imidacloprid may not be in high
enough concentrations in plant nectar to cause bee damage, the normal
process of converting nectar to honey will increase the concentration of
Imidacloprid by 2 to 3 times and could lead to the problems found in
French bees.
His final comments in the article are worth repeating verbatim.
“The reports of French Beekeepers and the greenhouse study on bumble
bees need to be taken serious. What Bayer has offered does not help to
understand the dilemma of the French bees or the results of the
greenhouse study on tomatoes and bumble bees. A study for sub-lethal
effects for a longer period of time is needed to explain the negative
impacts of Imidacloprid on bees. If Imidacloprid is not the culprit a
look at bee health in the affected region in France should be
warranted.”

end of article.

Scary stuff.
And it is used on many different plants, not just sunflowers. We are
watching the potato fields in Maine, where it is used. And the problem
is, if any Varroa are present, colony deaths may be masked and not
determined to be pesticide kills. Which is the purpose of the article,
to alert beekeepers to Gaucho. This was only one part of a much longer
article which also covered the French situation.
Bill Truesdell
Bath, ME