Abstract
The Australian plague locust, Chortoicetes terminifera (Walker), is an important agricultural pest and oviposits into compacted soil across vast semi-arid and arid regions prone to irregular heavy summer rainfall. This study aimed to quantify the effects of flooding (control, 7, 14, 21, 28 and 35 days) at different temperatures (15, 20 and 25°C) and embryonic development stages (25 and 75%) on egg viability, hatchling nymph body mass and survival to second-instar. Egg viability after flooding was dependent on temperature and flood duration. Eggs inundated at 15°C showed ≥53.5% survival regardless of flood duration and development stage compared with ≤29.6% for eggs at 25°C for ≥21 days early in development and ≥14 days late in development. Hatchling nymphs did not differ in body mass relative to temperature or flood duration, but weighed more from eggs inundated early in development rather than late. Survival to second-instar was ≤55.1% at 15 and 20°C when eggs were flooded for ≥28 days late in development, ≤35.6% at 25°C when flooded for ≥28 days early in development, and zero when flooded for ≥21 days late in development. These results suggest that prolonged flooding in summer and early autumn may cause very high egg mortality and first-instar nymph mortality of any survivors, but is likely to only ever affect a small proportion of the metapopulation. More common flash flooding for ≤14 days is unlikely to cause high mortality and have any direct effect on distribution and abundance.
Highlights
For terrestrial animals that inhabit environments prone to irregular heavy rainfall and the potential for flooding, the capacity to endure variable periods of inundation at different times of year is critical to survival
Egg survival was significantly decreased by increased flood temperature (d.f. = 2, F = 16.86, P < 0.001) and by increased flood duration (d.f. = 5, F = 6.08, P < 0.001)
A significant interaction whereby increased temperature and increased flood duration resulted in greater mortality was apparent (d.f. = 10, F = 2.20, P = 0.019), but interaction for increased temperature and development stage at inundation was marginally non-significant (d.f. = 2, F = 2.75, P = 0.066)
Summary
For terrestrial animals that inhabit environments prone to irregular heavy rainfall and the potential for flooding, the capacity to endure variable periods of inundation at different times of year is critical to survival. In Australia, vast semi-arid and arid inland areas are subject to high rainfall variability and sudden transitions between short but intense wet periods and long dry periods (Hughes, 2003; Pittock et al, 2006; Morton et al, 2011). This rainfall variability and the likelihood of flooding events are influenced by phases of the El Nino-Southern Oscillation in Eastern Australia as well as the Indian Ocean Dipole and Southern Annular Mode (King et al, 2013). Further increases in summer storm activity and frequency of flooding events are possible with anthropogenic climate change (Whetton et al, 1993; Hughes, 2003; Hirabayashi et al, 2013)
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