Negative effects of increased ozone concentrations and heat stress on bumblebees are exacerbated by microplastics

The intensity of environmental stressors increases due to global change. Under natural conditions, insect pollinators are experiencing multiple stressors simultaneously which may exacerbate the negative effects of individual stressors. Using a fully crossed factorial design, we investigated the effects of ozone, heat, and LDPE microplastics (MP) on Bombus terrestris health. Changes in the fat body proteome suggest that ozone induces an oxidative stress response, heat induces changes in the metabolism, and MP induces tissue damage responses and detoxification reactions. Among the single stressors, only MP increased bumblebee mortality. However, in combination with MP, also ozone, heat, and both combined increased the mortality. Here the effect strength exceeded expectations, suggesting synergistic effects. We presume a reduced heat resistance in MP-exposed bumblebees as one possible underlying mechanism. Our study suggests that the progressive environmental accumulation of MP, rising temperatures and the associated increase in ozone levels could pose a serious health risk to pollinators in the future.