Fungicide and climate warming drive bioenergetic reconfiguration across the life cycle of the European grapevine moth Lobesia botrana.

Understanding how multiple stressors interact is essential for predicting insect performance under global change. Although pesticide toxicity is well-established to be temperature-dependent, the physiological mechanisms underlying these interactions remain poorly understood. Insects often display stage- and sex-specific sensitivities to environmental pressures, suggesting complex energetic trade-offs across their life cycles. Copper-based fungicides, such as Bordeaux mixture, are widely used to control fungal diseases but can stress non-target insects. Here, we experimentally examined how Bordeaux mixture exposure interacts with projected late 21st-century climatic conditions by measuring growth rate, energy reserves, standard metabolic rate (SMR), and Hsp70 concentrations across larval instars (3rd and 5th) and adult sexes in the insect pest Lobesia botrana. Our results show that larvae underwent substantial physiological adjustments to fungicide exposure (increased Hsp70 concentrations, reduced SMR and glycogen), suggesting reallocation of energy from maintenance to stress protection. Future climatic conditions strongly modulated larval responses to the fungicide, shifting the timing of metabolic adjustments across development and interacting with Hsp70 production. Adults displayed sex-specific sensitivity to fungicide exposure, without major interaction with climatic conditions. Females exposed to the fungicide emerged with depleted reserves but unchanged SMR, consistent with energy allocation to reproduction. For males, Hsp70 concentrations were increased by fungicide exposure without major energy reserve loss, suggesting preservation of flight and mate-searching performance. Thus, stress responses are not simply additive but mediated through shared physiological pathways linking Hsp70 concentrations, metabolic regulation, and energy reserve mobilization. This study provides a mechanistic framework for understanding how interacting stressors reshape insect life-history strategies.