Temperature affects immersion tolerance of first-instar nymphs of the Australian plague locust, Chortoicetes terminifera

Abstract

The population dynamics of the Australian plague locust, Chortoicetes terminifera, are strongly linked to the timing and distribution of heavy rainfall events in semiarid and arid environments. While the effects of insufficient rainfall on survival are relatively well understood, little information exists on the effects of excessively wet conditions. This study aimed to quantify the survival of first-instar C. terminifera nymphs to a range of water-immersion periods and temperatures. Results show that survival is strongly dependent on immersion temperature whereby survival times ranged from time to 50% mortality (LT50) = 8.12 ± 0.26 h at 15°C to 4.93 ± 0.30 h at 25°C. Nymphs entered a coma-like state within 2 min of immersion. Post-immersion recovery times were greater for longer immersion periods and longer at higher temperatures for immersion periods of >3 h. These findings suggest that first-instar nymphs would be able to survive most instances of transient, localised pooling of water associated with heavy rainfall in the field. However, flooding that could trap individuals for >5 h (including nymphs still underground within the egg pod before emergence to the soil surface) has the potential to cause high mortality, particularly during summer and early autumn when water temperatures may be high.