Dehydration worsens heat tolerance of locusts and amplifies predicted impacts of climate change

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 heat exposure and the variation in heat tolerance among individuals in different physical conditions and at different life stages. 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 across a range of temperatures, we estimated tolerance of both chronic and acute exposures to high temperatures. We then used these data to model the injury and survival of locusts in microclimates of the past (1961–1990), present (1991–2020) and future (uniform warming of 3°C). Locusts succumbed to heat stress exponentially faster as temperature increased, but hydration state and life stage altered this exponential relationship. Our modelling indicated that recent climate change has amplified the risk of overheating, with predicted injury and survival depending strongly on a locust's access to shade and water. If changes in climate and land use reduce the availability of these resources, locust populations may shift their geographic range faster than currently predicted. To accurately predict range shifts and associated crop losses, mechanistic models of locust distributions should consider the combined stressors of heat and dehydration. Read the free Plain Language Summary for this article on the Journal blog.