Combined effects of rearing temperature and photoperiod on desiccation resistance in the water strider Aquarius paludum amamiensis

Desiccation resistance is an important physiological trait in insects, but how seasonal cues jointly affect this trait remains poorly understood in gerrid water striders. This study examined how temperature and photoperiod from the nymphal stage through early adulthood influence desiccation resistance in Aquarius paludum amamiensis (Miyamoto). First‐instar nymphs were reared under four combinations of high or low temperature and long‐ or short‐day photoperiod. Desiccation resistance was evaluated 30 days after adult emergence by measuring survival time, water loss at death, water loss rate and initial body water content. Survival time was significantly affected by temperature, photoperiod and their interaction, with the shortest survival under high‐temperature–long‐day conditions. Water loss rate also showed a significant interaction and was higher under high‐temperature–long‐day than high‐temperature–short‐day conditions. Initial body water content was generally lower at high than low temperature. Reproductive activity was strongly affected by temperature: Nearly all females reared at high temperature oviposited, and total egg production was substantially greater than at low temperature. Including wing morph as an explanatory variable did not alter the principal interactions. These results indicate that the effect of photoperiod on desiccation resistance depends strongly on temperature, with long‐day conditions reducing survival primarily at high temperature. Because reproductive activity was affected mainly by temperature, the interaction in desiccation resistance may involve photoperiod‐dependent regulation of water balance beyond reproductive maturation alone.