Imidacloprid discounted as source of bee die-offs; in-hive pesticides,
varroa, and nosema implicated again. Additionally, they associate higher
mortality with larger apiaries.
"Does Imidacloprid Seed-Treated Maize Have an Impact on Honey Bee
Mortality?" by: B. K. NGUYEN, et al. in: J. Econ. Entomol. 102(2):
616-623 (2009)
In the field, honey bees may be at risk via contaminated pollen and nectar
due to exposure to plants treated with the systemic insecticide
imidacloprid. However, when imidacloprid is fed to colonies in syrup or
pollen at amounts likely to be found in the fields, development and
survival of colonies are equivalent in treated and control colonies.
Schmidt (1996) showed that imidacloprid has no impact on sunflower
visitation by honey bees. In a field survey initiated in 2002 in French
apiaries, residues of imidacloprid were reported in 49% of pollen loads
from traps, but no honey bee colony mortality was observed. Despite these
results, the French government suspended the Gaucho registration for
sunflower in 1999 and for maize in 2004.
In Belgium, there is no commercial sunflower production, so Belgian
beekeepers have suspected imidacloprid maize treatments are responsible
for losses of honey bee colonies. The typical mortality rate of honey bee
colonies in Belgium is 10% (Haubruge et al. 2006). The rate was exceeded
in 50% of the apiaries observed in this study; mortality ranged from 0 to
84.2%.
Maize provides bees only with pollen, and we confirmed the presence of
maize pollen in bee hives. Chauzat et al. (2006) studied only the
pesticide residues in pollen loads and found imidacloprid in analyzed
samples but did not observe high honey bee mortality. Our study does not
support the involvement of maize treated with imidacloprid in the observed
mortality-related problems that affect honey bees in Belgium. However,
nutritive scarcity in the environment must be further studied.
The very large number of samples containing acaricides, especially
ineffective (tau-fluvalinate) or prohibited (rotenone, bromopropylate)
materials, to control V. destructor along with apicultural practices
highlighted during beekeeper interviews suggest the inadequacy of the
methods used for mite control. These parasites, along with the protozoan
Nosema ceranae and various viruses have recently been identified as
potential risk factors for honey bees mortality, which is described by
many experts as multifactorial.
--
Peter L Borst
Cohen Lab
VRT T3001
Cornell University
Ithaca NY 14853
http://web.me.com/peterlborst1
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