Greetings
I would like to point out that when the idea first surfaced that
beekeepers could be poisoning their own bees, I was very concerned that
such an idea should not be promoted without real evidence, because it
would weaken the beekeeping industry's case that they were in need of help
with an unknown contagious agent. But that was then; this is now.
There is still substantial indication that there may be contagious agents
involved, but there is also agreement that these could be opportunistic in
nature. It could very well be an underlying weakness in the honey bees'
immune response that is allowing nosema, varroa, virus, and pesticides to
"break the camel's back", as it were.
* * *
Pesticides have been a prime suspect in CCD research due to the known
weakness of honey bees in detoxification (a likely evolutionary
consequence of their habit of feeding on nectar and pollen, plant
materials that are low in toxin levels). Although there are no conclusive
findings to date, research continues to follow up on the analysis studies
examining the effects of individual compounds and combinations of
pesticide use on bee health to identify linkages to CCD.
To date, scientists have demonstrated a synergistic effect of two
pesticides in at least two studies, where the combination of the two
compounds was shown to be more toxic than either compound alone. In
addition, sub-lethal effects of the two common miticides, fluvalinate and
coumaphos, have been demonstrated, and scientists are testing a possible
link to a depressed immune system. Additional research is exploring a
possible link between sub-lethal pesticide exposure and increased pathogen
levels in honey bee colonies, which will help determine whether certain
pesticides are indirectly contributing to poor colony health and CCD.
-- USDA publication
* * *
Two-week-old worker bees, for example, are twice as susceptible to
coumaphos, when ingested in sugar water, than are 3-d-old bees. Drones
from Apistan-treated colonies were less likely to survive after emergence
as adults and weighed less than drones from untreated colonies. Queen
larvae exposed to coumaphos either failed to develop or showed
morphological and behavioral abnormalities, with more severe effects
observed in colonies with wax containing tau-fluvalinate residue from
prior Apistan treatment.
Queens that survived coumaphos exposure weighed less than queens that had
not been exposed to coumaphos. Although not addressed in this study, honey
bee brood may be at greater risk for suffering from synergistic
interactions as brood can be up to an order of magnitude more susceptible
to pesticides than adult bees. Larvae are also more likely to experience
continuous exposure to tau-fluvalinate and coumaphos through contact with
contaminated beeswax, in which they are effectively encased.
To manage varroa resistance to both tau-fluvalinate and coumaphos,
beekeepers have been encouraged to adopt a rotation program alternating
between Apistan and Checkmite. In light of the potential for synergistic
interactions between tau-fluvalinate and coumaphos, other miticides with
no known potential for P450 interactions, such as the organic acids should
be considered for management of varroa.
Further research is needed to determine the potential for the observed
synergism between coumaphos and tau-fluvalinate to harm whole bee colonies
and to elucidate the risk to bees posed by wax contaminated with years of
accumulated miticide treatments. The flagging effectiveness of the
miticides tau-fluvalinate and coumaphos, combined with their propensity to
accumulate in wax and synergize each other, is compelling evidence of an
urgent need to develop alternative approaches to varroa management in
commercial apiculture.
-- REED M. JOHNSON, HENRY S. POLLOCK, AND MAY R. BERENBAUM
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