Sitona weevil

sitona weevil, Sitona discoideus, scalloped leaf damage
Scalloped leaf damage.
Photo: Southern ute guide
sitona weevil, Sitona discoideus, greyish-brown adult with short broad snout
Adult sitona weevil. Photo: Southern ute guide

Scientific name

Sitona discoideus

Description

Larvae are up to 5 mm long, white-cream with an orange brown head, legless and have a slightly curved body. Adults are 5 mm long and are greyish-brown with three yellowish-white stripes behind the head and a short broad snout.

Similar species

Whitefringed weevil, vegetable weevil.

Distribution

Native to the Mediterranean region, now present in Europe, North Africa, South Africa, Australia and New Zealand.

Pest status

Major in South Australia, minor in New South Wales, Tasmania and Victoria, restricted and irregular.

Crops attacked

Lucerne, annual medics, subterranean clover.

Damage

Larvae feed within or on the root nodules and can cause more serious damage than adults by reducing nitrogen fixation and retarding plant growth. Older larvae feed on lateral and taproots. Adults make scallop-shaped notches along leaf margins and also chew the stems of seedlings and older plants.

Risk period

Damage is most severe in spring and autumn.

Life cycle

Eggs are laid in autumn in the soil around the base of plants and hatch with opening rains, when the emerging larvae burrow into the soil. Larvae feed through the winter and early spring to pupate in the soil and emerge as adults in late spring/early summer.

Monitoring

Inspect pastures for signs of seedling damage by adult weevils.

Action level

If adults are in large numbers and killing seedlings in autumn, chemical control may be required.

Control

Chemical control: If large numbers of adults are causing extensive leaf loss, control may be worthwhile. For current chemical control options see Pest Genie or APVMA.

Natural enemies: A sitona weevil parasitoid, Microctonus aethiopoides, was introduced to Australia as a biological control agent from the Mediterranean area. The parasitoid lays a single egg in the weevil´s body causing sterilisation and eventual death of the weevil.

Further information

Last updated 10 November 2010