Effects of sequential exposures of sub-lethal doses of amitraz and thiacloprid on learning and memory of honey bee foragers, Apis mellifera

Pollinators, honey bees in particular, are continuously exposed to various mixtures of pesticides, which contribute to their population decline. Both amitraz and thiacloprid have been proven less toxic to honey bees and are frequently applied in- and out-hive, respectively. We examined the sub-lethal effects of amitraz, thiacloprid and their sequential exposure on learning, memory and sugar responsiveness in Apis mellifera using the Proboscis extension response (PER). Sub-lethal doses of amitraz (0.1, 0.2 and 0.4 mu g/bee) and thiacloprid (0.05, 0.1 and 0.2 mu g/bee) were tested. Sub-lethal effects were observed only at the highest doses of each pesticide treatment; amitraz (0.4 mu g/bee) and thiacloprid (0.2 mu g/bee) but not in lower doses. In sequential treatment of amitraz and thiacloprid, reduced acquisition and memory retention were significant across all tested doses. The same profile was also obtained on sugar responsiveness of foragers. Our results suggest that the sequential exposure would pose higher risk to honey bee compared to single pesticide exposure by reducing the bees' appetitive olfactory learning, memory and sugar acuity more than individual pesticide exposures.

Automated summary

The study found that sequential exposure to amitraz and thiacloprid affected honey bees' learning, memory, and sugar response. High doses of pesticides significantly reduced bees' acquisition and memory retention abilities.