High-temperature survival is limited by food availability in first-instar locust nymphs

Abstract

The Australian plague locust, Chortoicetes terminifera (Walker), is often exposed to high temperature and low humidity in semiarid and arid environments. Early-instar survival under these conditions is an important prerequisite for the formation of high-density aggregations in summer and autumn generations. The present study investigates how first-instar C. terminifera respond to high temperature and low humidity using measures of total body water content, physiological and behavioural transitions during temperature increase, critical upper limit, and mortality relative to food availability. The critical upper limit for fed nymphs was very high at 53.3 ± 1.0°C, with death preceded by a clear progression of changes in behaviour, gas exchange, water loss and excretion. At more ecologically relevant high temperatures, food availability allowed nymphs to behaviourally respond to increased water loss, and the resulting physiological maintenance of water reserves provided cross-tolerance to heat relative to exposure duration and maximum temperature as well as the rate of warming. While very high mortality was recorded at ≥45°C in 6-h direct-exposure experiments, a highly exposed and very poorly vegetated summer environment would be required for local population failures from current high temperatures and low humidity alone.