Lethal and sublethal effects of a frequently used pesticide synergist, piperonyl butoxide (PBO), on the common eastern bumblebee (Bombus impatiens)

Piperonyl butoxide (PBO) is a common ingredient in many pesticide formulations and when combined with certain insecticides, like pyrethroids, PBO increases their toxicity. Considered nontoxic on its own, little research has been done to confirm whether PBO affects important pollinators, such as the common eastern bumblebee (Bombus impatiens), at environmentally realistic exposure levels. Using the Environmental Protection Agency’s BeeREX tool to estimate pollen and nectar contamination after spraying, individual B. impatiens were exposed orally to a low concentration of PBO (0.5 ppm) alone or in combination with a pyrethroid insecticide, bifenthrin. Bees exposed to PBO alone or in combination with the pyrethroid showed a significant decrease in locomotor activity 48-hr post-exposure. Next, we exposed B. impatiens microcolonies to a medium concentration of PBO (5 ppm) twice during a four-week bioassay. There were no significant differences in B. impatiens mortality, sucrose consumption, or number of larvae produced upon conclusion of the experiment. Finally, individual B. impatiens workers were exposed orally to high, medium, or low concentrations of PBO (55, 5, or 0.5 ppm, respectively) and survival was monitored over six weeks compared to sham-inoculated control bees. Bees exposed to the high concentration of PBO experienced significantly lower survival compared to control sham-inoculated bees, while there was no difference in survival of medium- and low-exposure bees compared to controls. Despite being considered an inert ingredient in pesticides, these results indicate that PBO is toxic enough at environmentally realistic concentrations to disrupt behavior and reduce survival of a native non-target pollinator, B. impatiens.