Short-term exposure to heatwave-like temperatures affects learning and memory in bumblebees

Global warming has been identified as a key driver of bee declines around
the world. While it is clear that elevated temperatures during the spring
and summer months – the principal activity period of many bee species – is
a factor in this decline, exactly how temperature affects bee survival is
unknown. In vertebrates, there is clear evidence that elevated ambient
temperatures impair cognition but whether and how heat affects the
cognitive abilities of invertebrates remains unclear. Cognitive skills in
bees are essential for their survival as, to supply the hive with
nutrition, workers must be able to learn and remember the location of the
most rewarding floral resources. Here, we investigate whether
temperature-related cognitive impairments could be a driver of bee
declines by exploring the effect of short-term increases in ambient
temperature on learning and memory. We found that, in comparison to bees
that were tested at 25°C (a temperature that they would typically
experience in summer), bees that were exposed to 32°C (a temperature that
they will becoming increasingly exposed to during heatwave events) were
significantly worse at forming an association between a coloured light and
a sucrose reward and that their capacity to remember this association
after just 1 hour was abolished. This study provides novel experimental
evidence that even just a few hours of exposure to heatwave-like
temperatures can severely impair the cognitive performance of insects.
Such temperature-induced cognitive deficits could play an important role
in explaining recent and future bee population declines.