contaminated maize and winter bee rearing
Quote:
Originally Posted by
gavin
I'm in favour of always keeping an open mind on pesticides (in both directions) and wouldn't want to rule out an involvement in these German bee losses, but ..... there is plenty of existing data which points firmly away from farm pesticides. You could argue, of course, that the sampling in this study was directed to oilseed rape and not maize, but nevertheless surely maize will not be that different?
I had a lengthy discussion this mornig with some German beekeepers. We were wondering if the difference lies in the different flowering times of maize and oilseed rape:
At the time oilsseed rape is in flower there are in general plenty of other pollen sources available which are not contaminated by the systemic pesticides. The bees reared at this time are summer bees which are not expected to live very long, the turnover in the colonies is high.
At the time when maize is flowering there are usually very few alternative pollen sources available and the bees are forced to rear the brood on the contaminated maize pollen. The bees reared now are the winter bees which are meant to be very long lived and they need extra fat reserves in their body.
The consequences:
These compromised winter bees will suffer a shortened lifespan and decreased immunity. Also, as the systemic pesticides are neurotoxins, the bees' ability to detect varroa could be diminished, in which case fewer mites will be removed, allowing a massive build-up in the colony as we have seen in so many cases.
Those colonies that manage to shake off varroa can make it through to spring, but succumb to nosema due to suppressed immune system or their bee numbers dwindle away due to the shortened lifespan. (Marie Celeste syndrome)
The reason why some colonies are less affected than others could lie in their foraging preferences: some might fly out of their way to collect uncontaminated pollen.
Or it could be due to timing: some colonies might produce their winter bees earlier or later than the maize flowering time and so avoid the heaviest pesticide loads.