Spodoptera exempta (Walker, 1856)
(one synonym:
Agrotis bipars)
African Armyworm
AMPHIPYRINAE ,
NOCTUIDAE
Don Herbison-Evans (
donherbisonevans@yahoo.com )
&
Stella Crossley
(updated 21 August 2008)
These Caterpillars
vary their colour according to their
degree of crowding. If sparse, they are inclined to be green.
If crowded they become black. This correlates with
an increased resistance to disease if crowded.
They are an international pest, feeding on various grasses (
POACEAE ), including:
Para Grass ( Brachiaria mutica ),
Rice ( Oryza sativa ),
Dallisgrass ( Paspalum dilatatum ),
Kikuyu ( Pennisetum clandestinum ),
Sugar Cane ( Saccharum officinarum ), and
Sorghum ( Sorghum bicolor ).
They are initially green, but later
instars
are brown with black stripes.
They can advance in a mass across field, consuming the grass as they go
(hence the term "Armyworm"). They do this blatently in full daylight.
This is extensively illustrated in the BBC video "War of the Worlds"
in their series:
"Alien Empire".
The young Caterpillars only eat the surface layer of the leaf,
but later they eat large pieces out of the sides of the leaves.
(Photo: courtesy of
Holt Studios)
The adult moth is brown with a pattern
of light and dark markings on each forewing.
The
pheromones of this species have been determined.
The adult moth has a wingspan of about 4 cms.
(Photo: courtesy of
Rice IPM)
The species occurs in :
Australia's north,
Africa,
Hawaii,
New Zealand, and
USA.
It undertakes periodic
migrations, which complicate the control of the species.
These have been
observed by radar.
It might be controlled by :
digging a ditch in front of them, as they then find the
extensive section of loose soil too difficult to scale,
the bacterium
Bacillus thuringiensis (
BACILLACEAE ),
the nematode
Steinernema carpocapsae (
STEINERNEMATIDAE ),
a
Cypovirus (
REOVIRIDAE ), and
trapping using
artificial pheromones.
Further reading :
J.R. Agnew (ed.), Australian Sugarcane Pests,
Bureau of the Sugar Experiment Stations (Indooroopilly),
1997, pp. 54-55.
Ian F.B. Common,
Moths of Australia,
Melbourne University Press, 1990, pp. 42, 65, 462.
