Photoperiod‐Regulated Thermal Tolerance of the Non‐Diapausing Insect <i>Ceratitis capitata</i> (Diptera: Tephritidae)

ABSTRACT Understanding how photoperiod influences thermal tolerance in non‐diapausing tropical pest species is critical for predicting their invasion potential and resilience under climate variability. This study investigates, for the first time, the effects of photoacclimation on thermal tolerance (CT min and CT max ) of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), a globally significant agricultural pest. Two controlled laboratory experiments were conducted. In the first, all immature stages (egg to adult) were reared under four photoperiod regimes (0:24, 8:16, 14:10, and 24:0 L:D) at constant laboratory conditions (25°C ± 1°C, 55% ± 10% RH, and 1000 ± 200 lx). In the second experiment, all immatures were reared under a common long‐day photoperiod (14:10 L:D). The emerging adults of both experiments were subsequently exposed to the same four photoperiods for 10 days. Critical thermal limits were assessed on day 11 of adult life. Results showed that photoperiod during development significantly affected both CT min and CT max . Flies reared under long‐day conditions exhibited the lowest CT min , while those under short‐day conditions had the highest. The highest CT max values were recorded in adults reared under constant darkness, particularly in females. In contrast, when only adults were photoacclimated, CT min remained unaffected, but CT max was significantly lower under constant light compared to other treatments. These findings reveal that photoperiod alone, independent of temperature, can modulate thermal tolerance in C. capitata , with developmental exposure having a stronger effect than adult‐only acclimation. This study highlights the importance of incorporating photoperiodic cues into thermal biology and invasion ecology frameworks. Understanding how light regimes shape physiological limits can improve predictions of pest establishment in novel environments and inform more ecologically realistic pest management strategies.