Climate change is altering the timing of hatching in bees and wasps, causing earlier emergence after winter
Warmer temperatures can leave insects out of sync with food sources such as flowers and prey
Faster depletion of fat reserves in warmer conditions reduces survival and reproductive success
Some summer females lost up to 34% of their body mass under higher temperatures
Study highlights risks to pollination and calls for deeper research into climate impacts on insect populations
Climate change is altering the timing of emergence, or hatching, after hibernation in bees and wasps worldwide, adversely affecting their physical fitness, a new study has found.
The research, published in the journal Functional Ecology, shows that rising temperatures are forcing insects to adjust their seasonal timing. Warmer conditions are prompting earlier hatching in spring or summer, which can leave insects out of sync with the availability of flowers or prey. In such cases, newly emerged insects may struggle to find food, as flowering or prey cycles may not yet have begun.
Higher temperatures accelerate the depletion of fat reserves in hibernating adults, reducing their chances of survival and reproduction, the study found.
Researchers analysed the emergence timing of 14,921 individuals from five cavity-nesting bee and wasp species — Osmia bicornis, Chelostoma florisomne, Trypoxylon figulus, Heriades difformis and Heriades truncorum.
The insects were collected from 161 sites across Bavaria in southern Germany, covering a temperature range of 5.9 degrees Celsius (°C) to 10°C. They were then studied under controlled laboratory conditions simulating cold, warm and hot post-winter scenarios to identify potential genotype-environment interactions.
All insect groups emerged earliest under hot conditions and latest under cold treatments, demonstrating clear shifts in behaviour linked to temperature.
The response to warming varied across species. Osmia bicornis showed the strongest reaction, emerging earliest among spring species under warmer conditions. This behaviour may reflect an adaptive strategy to avoid emerging too early in colder environments where food is scarce.
In contrast, Heriades truncorum, typically a late-emerging species in colder conditions, showed a counterintuitive response by emerging earlier than its warm-region counterparts. Researchers suggest this may be linked to faster development rates needed to complete its life cycle within shorter summers.
Another species, Heriades difformis, which emerges mid-season, showed little variation in timing across different temperature conditions, maintaining a consistent emergence pattern.
“The bee emerging in mid- season, H. difformis, was the only species for which neither females nor males showed changes in emergence with multi-annual mean temperatures but consistent timing in response to post- winter temperature treatments,” the study said.
The study also noted that deviations in temperature during development influenced timing, with spring species emerging earlier in warmer-than-average years.
Warmer conditions were associated with significant physical costs. “In spring species, mass loss was higher in warmer post-winter treatments, with the strongest reductions observed in cool-adapted individuals,” the study noted. Mass loss was especially pronounced among summer females, with some individuals losing up to 34 per cent of their body mass. In several species, females lost weight more rapidly than males, suggesting they face greater pressure to conserve energy, likely for reproduction.
In Heriades truncorum, females in warmer treatments emerged earlier and within a shorter period, retaining higher body mass compared to those in colder conditions. “The observed female-specific pattern supports the idea that conserving fat reserves is more crucial for females,” the findings underlined.
While bees and wasps show a degree of flexibility in adapting to temperature changes, the researchers warn that predicting long-term impacts on populations and communities requires a deeper understanding of how local adaptations to climate may affect individual fitness and responses to new conditions.
They highlight several key questions for future research: how additional days of extreme heat affect emergence, how energy reserves influence pollination performance, and how quickly insect populations can adapt to rapidly changing climates.