Dehydration worsens heat tolerance and predicted survival of locusts

By increasing the mean and variance of environmental temperatures, climate change has caused local extinctions and range shifts that are likely to intensify over time. Previously, biologists projected impacts of climate change from the acute heat tolerances of adult organisms; however, this approach ignores important factors, such as the cumulative damage from chronic heat exposure and the variation in heat tolerance among individuals in different physical conditions and at different life stages. To address these issues, we measured the effects of hydration state and life stage on the heat tolerance of an agricultural pest, the South American locust (Schistocerca cancellata). By measuring tolerance time at twelve stressful temperatures ranging from 46.5℃ to 52℃, we estimated heat tolerance at multiple time scales ranging from five minutes to six hours. We then used these data to model the survival of locusts in microclimates of the past (1961-1990), present (1991-2020), and future (uniform warming of 3°C). We modeled the microclimates near La Rioja of Argentina (latitude: -29.32588, longitude: -65.94552, elevation: 275 m), where locust populations have persisted since the 1950s. Our experiment indicated that, as expected, locusts succumbed to heat stress exponentially faster as temperature increased, but hydration state and life stage both altered this exponential relationship. Our model indicated that climate change has already amplified the risk of overheating, particularly if locusts cannot access shade or water.