Honeybees fail to discriminate floral scents in a complex learning task after consuming a neonicotinoid pesticide

Neonicotinoids
are pesticides used to protect crops but with known secondary influences at
sublethal doses on bees. Honeybees use their sense of smell to identify the
queen and nestmates, to signal danger and to distinguish flowers during
foraging. Few behavioural studies to date have examined how neonicotinoid pesticides
affect the ability of bees to distinguish odours. Here, we use a differential
learning task to test how neonicotinoid exposure affects learning, memory, and
olfactory perception in foraging-age honeybees. Bees fed with thiamethoxam could
not perform differential learning and could not distinguish odours during short
and long-term memory tests. Our data indicate that thiamethoxam directly
impacts the cognitive processes involved in working memory required during
differential olfactory learning. Using a combination of behavioural assays, we
also identified that thiamethoxam has a direct impact on the olfactory perception
of similar odours. Honeybees fed with other neonicotinoids (clothianidin,
imidacloprid, dinotefuran) performed the differential learning task, but at a
slower rate than the control. These bees could also distinguish the odours. Our
data are the first to show that neonicotinoids have compound specific effects
on the ability of bees to perform a complex olfactory learning task. Deficits
in decition-making caused by thiamethoxam exposure could be more harmful than
other neonicotinoids, leading to inefficient foraging and a reduced ability to
identify nestmates.