Effects of substrate salinity on oviposition, embryonic development and survival in the Australian plague locust, Chortoicetes terminifera (Walker)

Abstract

The Australian plague locust, Chortoicetes terminifera (Walker), is an important agricultural pest that oviposits into soil across vast semi-arid and arid regions. This study aimed to determine whether gravid female locusts can discriminate among substrates of increasing salinity (0, 4, 8, 12, 16, 20, 24, and 28ppt NaCl) when attempting oviposition, and quantify the effects of saline substrate on direct developing egg viability, and subsequent hatchling nymph body weight and survival. Gravid female locusts increasingly excavated and withdrew prior to completing oviposition in substrates of increasing salinity, but similar numbers of completed egg pods were observed across treatments. Egg weight at 50% total development time and successful egg development to nymph emergence decreased with increasing substrate salinity. Water balance equilibrium between the egg and the substrate occurred at approximately 12ppt NaCl corresponding to a water activity of ∼0.995. Eggs oviposited into sand containing ⩽12ppt NaCl weighed ⩾6.26±0.91mg and had ⩾76.8% successful development to nymph emergence. Eggs oviposited into sand containing >12ppt NaCl weighed ⩽5.16±1.27mg and had ⩽45.6% successful development to nymph emergence. Hatchling nymph body weight and survival to second instar also decreased with increasing substrate salinity. Nymphs that hatched and emerged from sand containing ⩽12ppt NaCl weighed ⩾5.55±0.43mg at emergence and had ⩾68.9% survival. Nymphs that hatched and emerged from sand containing >12ppt NaCl weighed ⩽5.28±0.67mg at emergence and had ⩽52.0% survival. These results indicate that C. terminifera is sufficiently resilient to develop and survive in saline substrates over most of their range.