The role of water temperature and food availability in shaping immunity and body condition of Odonata: Impacts of deprivation on larval development

Global climate change and intensified human activities are increasingly affecting aquatic ecosystems, including Odonata, whose life cycles and physiology are closely linked to freshwater conditions such as temperature and food availability. While patterns influencing their distribution and abundance are well documented, physiological responses to anthropogenic stressors remain less understood. In this ex situ laboratory experiment, we examined the effects of water temperature and food availability on larvae of Aeshna cyanea Müller, 1764 (Odonata: Aeshnidae) by assessing body condition and immune function. Larvae were reared for 2 months at either 17 or 21°C, and within each temperature treatment, individuals were fed either three times per week or once per week to simulate food limitation. Elevated temperature reduced haemocyte density, but this effect depended on feeding frequency, with the negative effect of higher temperature being less pronounced under greater food availability. Food availability was a major driver of larval performance, with increased feeding promoting growth, fat stores, protein concentration and phenoloxidase (PO) activity. Conversely, there was marginal evidence that elevated temperature weakened the positive effect of increased feeding on fat accumulation. Faster growth was associated with lower protein concentration and PO activity, suggesting a potential allocation trade‐off between somatic growth, physiological condition and immune function. Together, these results show that temperature and food availability can influence larval performance both independently and interactively, providing insight into physiological mechanisms that may contribute to the vulnerability and decline of Odonata populations under changing environmental conditions.