Lifecycle
The Australian plague locust has three stages in its lifecycle – egg, hopper and adult.
In the south-west of Western Australia the locust can complete two generations each year; the first generation occurring through winter, spring and summer and the second generation through summer and autumn.
Differences between Australian plague locusts and wingless grasshoppers
Australian plague locusts are sometimes found with a range of other, similar looking species of non-winged grasshoppers. The Australian wingless grasshopper (Phaulacridium vittatum), is often confused with the Australian plague locust, especially at the immature stage.
Australian wingless grasshoppers strongly vary in colour from dark grey to almost black (never green), but 40% of the population have wings and can fly.
At the hopper stage, locusts as well as wingless grasshoppers, are only 15-20mm long and distinguishing features such as shape, colour and wing veins are very variable and hard to see.
Australian plague locusts always have an x-shaped marking behind the head. In nymphs this can be faded and becomes more visible with maturity, but it is always present.
Wingless grasshoppers sometimes have no patterns at all.
Distinguishing Australian plague locusts from other grasshopper and locust species
Adults
Adult Australian plague locusts have a dark spot on the otherwise clear hind wing. The dark spot looks like an elongated smudge. They also have red tibia. This distinguishes them from all other species.
Male Australian plague locusts are 27mm and females are 32mm in length.
Some Australian locust/grasshopper species from the genus Austroicetes can have similar X-shaped marks but never have a red tibia and a dark spot on the hind wing.
Three commonly Austroicetes species found in the same areas as Australian plague locusts are:
Confusing Austroicetes (Austroicetes pusilla), which have a yellow or pink hind tibia, males are 14mm and females 20mm in length. Rarely found in high densities.
Small plague locust (Austrocietes cruciata), whose colour and pattern are highly variable, hind tibia is usually yellow, males are 14mm and females 25mm in length. This species can be found in high densities, can form swarms but these are not known to move great distances, about 35km is the maximum dispersal rate.
South-eastern Austrocietes (Austrocietes vulgaris), whose colour and pattern is highly variable. Hind tibia has a basal black or brown band, tibia can be reddish in colour. Males are 12mm and females are 23mm in length. This species has been recorded as causing crop damage in concert with other grasshopper/locust species.
Hoppers
Australian plague locust hoppers (third instar) can be distinguished from other hoppers by:
- transverse bands on the femur
- posterior (bottom) half of X-shaped marking is distinct
- lateral (side) surface of head and thorax is mottled
- hind tibia with light coloured collar
Later instars have more pronounce X-shaped markings on thorax, hind tibia retains collar.
Confusing Austroicetes (Austroicetes pusilla) have:
- indistinct X-shaped marking
- hind femur with single black band
- lateral (side) surface of head and thorax with white triangular marking
- hind tibia with collar and cross-bar
In later instars background colour remains pale, white triangular markings become indistinct.
Small plague locust (Austrocietes cruciata) have:
- X-shaped marking on thorax
- hind femur obliquely banded
- lateral (side) surface of head and thorax with white triangular marking
- hind tibia uniformly dark
Later instars have uniformly light coloured tibia.
South-eastern Austrocietes (Austrocietes vulgaris) have:
- anterior (top) half of X-shaped marking distinct
- hind femur transversely banded
- lateral (side) surface of head and thorax with white triangular marking
- hind tibia with white collar and cross-bar
Later instars retain general form, hind tibia has white collar and cross-bar.
References
Baker, G. L. 1984. Field guide to nymphs of grasshoppers and locusts in New South Wales. Advisory Bulletin 2, Department of Agriculture New South Wales.
Key, K.H.L. 1992. Taxonomy of the genus Phaulacridium and a related new genus (Orthoptera: Acrididae). Invertebrate Taxonomy, vol. 6, 197-243.
Rentz, D.C.F., Lewis, R.C., Su, Y.N., & Upton, M.S. (2003) A Guide to Australian Grasshoppers and Locusts. Natural History Publications (Borneo). Kota Kinabalu.