The effect of pymetrozine (Plenum WG-50®) on proboscis extension conditioning in honey bees (Apis mellifera: Hybrid var. Buckfast)

Experiments are designed to examine the effects of pymetrozine (Plenum WG-50®), a recent systemic pesticide of the pyridine-azomethin family, on Pavlovian conditioning of harnessed foragers. In one set of experiments bees learned a task in which they associated a conditioned stimulus with feeding. A second set of experiments required the bees to learn a discrimination task. Within each experiment, bees received 5 μl of sucrose only, the recommended field dose of Plenum® (5 μL of .3 g L−1, .16 g L−1 of pymetrozine measured), or 100 times the field dose of Plenum® WG 50 thirty minutes prior to training (5 μL of 30 g L−1, 14 g L−1 of pymetrozine measured). The Plenum® WG 50 was diluted with .88 M sucrose to facilitate the drinking of the pesticide. In addition to varying the concentration, we also investigated the effect of Plenum® WG 50 on bees confined to an observation hive and a hive located outside. The results indicated that prior exposure to Plenum® WG 50 affected Pavlovian conditioning only when bees were exposed to 100 times the recommended dosage.

► We study the effects of pymetrozine on Pavlovian conditioning of honeybees.
► We examine learning of harnessed foragers in both simple and complex learning.
► Pymetrozine at recommended amounts do not influence learning.
► Pymetrozine at 100× recommended amounts influence learning.
► Effect of pymetrozine on honey bee learning depends on the concentration.