"Even if it does not kill the brood, it will certainly stress it."

There is a huge difference between an acute exposure and a chronic exposure in terms of damage done.  Take a single exposure with a LD 50 of 1 unit.  Now do a two week feeding study and you might find a no effect level of as much as 0.25 or 0.5 units fed daily.  Or you might also find a no effect level of 0.1.  As you go to longer exposures the amount fed per day that gives a no effect level often, but not always, continues to drop.  How fast it drops is totally unpredictable.  This is why in tox studies you do a LD50 first, then generally a two week feeding study, then a 30 day feeding study, then 60 days, then 120 days out to in a mouse or rat case the life of the animal.  You simply can not take a LD50 and have any idea what will happen on much longer exposures.  The net result is that chemical that had an LD50 of 1 unit might cause all kinds of problems at a dose of 0.01 unit fed daily for a year.  Or you might find the no effect level in a one year study was 0.1 units or even 0.5 fed daily.  Due to the short natural life of honey bees over summer they might be ok.  But winter bees live longer and so do queens and what did not bother summer bees could well be a problem for winter bees or queens.

Dick

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