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

Abstract 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 environmentally relevant ozone levels, 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. We observed MP to have the strongest effect on mortality among the single stressors. Only in combination with MP, ozone, heat, and both combined significantly increased the mortality. For the combination of all three stressors, the effect strength exceeded expectations, indicating synergistic effects. We propose 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.