The response of Mitchell grasses (Astrebla spp.) and Button grass (Dactyloctenium radulans (R. Br.)) to rainfall and their importance to the survival of the Australian plague locust,Chortoicetes terminifera (Walker), in the arid zone

The environmental conditions that allow the growth of Barley Mitchell grass, Astrebla pectinata, and the development of the Australian plague locust, Chortoicetes terminifera, are similar. A single fall of more than 20 mm rain and a mean monthly maximum temperature above 23°C ensures sustained growth of Barley Mitchell grass and hatching of eggs of the Australian plague locust. Curly Mitchell grass, Astrebla lappacea, is found in heavier clay soils and requires about 40 mm to respond. Both Mitchell grasses normally remain green for about 2 months after rain which is slightly longer than the duration of locust development to the adult stage. As a result, locusts in Mitchell grass areas can complete their development to migration and laying on a single substantial fall of rain: an adaptation of critical importance in the arid zone where follow-up rain is unlikely. Under similar circumstances, ephemerals like Button grass, Dactyloctenium radulans, are dry in approximately 6 weeks. The locusts are usually at the late nymphal stage by this time and even though Mitchell grass is still quite green, nymphal growth is retarded, resulting in adults which are smaller than normal. These adults are able to accumulate the fat needed for migration by feeding on the dry green Mitchell grasses. In the absence of dry green or green Mitchell grass, the locusts persist locally and die without laying unless there is further rain.