WARMING AND INCREASED RAINFALL REDUCE BUMBLEBEE QUEEN FITNESS

How populations respond to climatic change depends on how climate affects individual growth, survival and reproduction – traits that ultimately shape population dynamics. However, climate can have complex effects on these traits and long-term data linking insect life-histories and climatic variation are rare.

Here, we test how climate affects health, survival and reproduction in wild Bombus terrestris queens caught over 15 years after emerging from hibernation. We relate climate variation experienced by queens as they developed in their natal colonies and entered hibernation, to fitness traits assayed under constant lab conditions.

We show that wet years consistently reduced queen fitness, while warm temperatures had positive and negative impacts. Behind these annual effects, lies strong seasonality. In particular, climatic conditions experienced by young queens as they forage, mate and enter hibernation are vital in determining whether they reproduce the following spring.

Results suggest that these climate effects are partly due to resources: climatic drivers that reduce resource acquisition prior to hibernation, or disrupt diapause and thus accelerate resource loss over winter, are especially detrimental to spring queen fitness. While results show potential for increasingly negative effects of climate change on bumblebees, they also inform mitigation strategies; providing high-quality forage in late summer, before queens enter diapause.