Predation Under Heat Stress: The Significance of Body Size to the Outcome of an Acarine Predator–Prey Interaction

, when separately exposed to mild or extreme heat waves during juvenile development: adult predator-prey size ratios shifted from 0.83 under mild heat waves to 0.60 under extreme heat waves. Thus, firstly, experiments were conducted under optimal temperature (25°C) to evaluate the effects of shifted body size ratios on prey survival. Second, we asked whether these asymmetric thermal alterations of the adult sizes also affect prey survival under heat. Single couples of adult predator and prey females, reared under mild or extreme heat waves, were placed on a leaf disc and exposed to mild or extreme heat (corresponding to the daily temperature peaks during juvenile development) and were videotaped for 90 min. Under optimal thermal conditions, the survival rate of prey females was highest when both species were reared under extreme heat waves, emphasizing the importance of carry-over effects from thermal juvenile environment to adult performance. At extreme heat, prey survival was 76% compared with 42% at mild heat. The predator-prey body size ratio in favor of the prey under extreme heat wave conditions was a strong predictor of predation success. This outcome is in line with the trophic sensitivity hypothesis, stating that prey is less sensitive to heat stress than its predator. We attribute this to the fact that predators become smaller and prey larger the higher the temperature is during juvenile development. Such asymmetric thermal effects may constitute a serious obstacle for achieving successful biological control of spider mites during heat waves.