Honey bees exposed to sub-lethal doses of imidacloprid in laboratory and field experiments

In this study, different context-dependent effects of imidacloprid exposure on the honey bee
response were studied. Honey bees were exposed to different concentrations of imidacloprid during a time period of 40 days. Next to these variables, a laboratory-field comparison
was conducted. The influence of the chronic exposure on gene expression levels was determined using an in-house developed microarray targeting different immunity-related and
detoxification genes to determine stress-related gene expression changes. Increased levels
of the detoxification genes encoding, CYP9Q3 and CYT P450, were detected in imidacloprid-exposed honey bees. The different context-dependent effects of imidacloprid exposure
on honey bees were confirmed physiologically by decreased hypopharyngeal gland sizes.
Honey bees exposed to imidacloprid in laboratory cages showed a general immunosuppression and no detoxification mechanisms were triggered significantly, while honey bees infield showed a resilient response with an immune stimulation at later time points. However,
the treated colonies had a brood and population decline tendency after the first brood cycle
in the field. In conclusion, this study highlighted the different context-dependent effects of
imidacloprid exposure on the honey bee response. These findings warn for possible pitfalls
concerning the generalization of results based on specific experiments with short exposure
times. The increased levels of CYT P450 and CYP9Q3 combined with an immune response
reaction can be used as markers for bees which are exposed to pesticides in the field.

De Smet L, Hatjina F, Ioannidis P, Hamamtzoglou A, Schoonvaere K, Francis F, et al.
(2017) Stress indicator gene expression profiles, colony dynamics and tissue development of honey bees exposed to sub-lethal doses of imidacloprid in laboratory and field experiments. PLoS ONE 12(2): e0171529. doi:10.1371/journal.pone.0171529