Insect adaptation to urban environments: A synthesis of morphological, behavioural, and physiological responses.

Urbanisation is among the most pervasive drivers of contemporary environmental change, imposing a complex suite of abiotic and biotic pressures on insect populations worldwide. Here, we synthesize recent evidence on how insects respond to urban environments across three interconnected axes: morphology, behaviour, and physiology. Urban heat and dry islands, habitat fragmentation, artificial light at night, noise, air and chemical pollution, and novel plant communities act as multidimensional filters that can drive shifts in body size, locomotory appendage, coloration, foraging and mating behaviours, activity patterns, thermal physiology, water balance, stress metabolism, and seasonality. These changes in morphology, behaviour, and physiology do not act independently but instead form an integrated functional response to urban environments. Moreover, multiple urban stressors, sometimes acting in opposing directions, can interact to shape trait responses. We further discuss the concept of urban trait syndromes, wherein suites of correlated traits co-vary or are co-selected under shared urban pressures. Insect responses to urbanisation arise through both phenotypic plasticity and evolutionary adaptation, though disentangling their relative contributions remains a key challenge. In some case, maladaptive responses can arise when historically reliable cues become decoupled from fitness in novel environments. Finally, we identify critical knowledge gaps, including the need for more multi-stressor experiments, greater taxonomic and geographic coverage, and long-term studies that track the pace and limits of urban adaptation.