in toxicity as great as 100-fold relative to that which would be predicted
from a strictly additive model (Thompson, 1996). For example,
exposure to field-relevant concentrations of the neonicotinoid
imidacloprid and the OP coumaphos impaired olfactory learning
and memory formation in honey bees (Williamson and Wright,
2013). In a study with four common pesticides (fluvalinate, coumaphos,
chlorothalonil, and chloropyrifos), exposure to field-relevant
concentrations either individually or in mixtures caused significant
increases in larval mortality. Synergistic effects were observed
with certain binary mixtures, but a combination of the OPs chlorpyrifos
and coumaphos resulted in only additive toxicity (Zhu
et al., 2014).
The objective of the present study was to assess whether exposure
to environmentally relevant concentrations of a mixture of
OPs exerts adverse effects on honey bee workers. Effects of the
mixture of OPs on survival, behavior, activity of AChE, and expression
of genes involved in detoxification and immune response,
were quantified. It was hypothesized that exposure of bees to a
mixture of OPs that act via the same mode of action could exert
adverse additive effects on the endpoints examined in individual
bees.