Vegetable Weevil

Listroderes difficilis

Family: Curculionidae

Order: Coleoptera

Description:

Adult

Nocturnal and hides in the ground during the day.

Colour - Dull grey. Pale V marks near rear.

Body - Slightly flattened. 5 mm long, 2 mm wide.

Wings - 2 Pairs. Front wings modified to form hard protective cases (elytra) for rear wings. When at rest they meet in a straight line down the centre of the back. Rear wings membranous and folded both lengthwise and across so they fit under their protective cases. When in flight the elytra are held at an angle and the rear wings beat rapidly. Rear wings may be reduced or absent. Wing-span up to 10 mm. Both pairs attached to the hind body.

Mouthparts - Chewing. Pointing forward. Has a typical weevil snout.

Antennae - 7-11 segments.

Legs - Rear legs larger than front legs. Feet (Tarsi) have 3-5 segments with 1 or 2 claws on the end segment.

Head - Rigid. Large rounded compound eyes.

Thorax - Front segment associated with head to form distinct fore body. Front segment covered by a hard plate (pronotum). 2 rear segments fused and associated with the abdomen to form hind body.

Abdomen - 10 segments in male, 9 in female. Often only 8 can be counted by eye. Spiracles on segments 1-7 and often on 8 also.

Egg - Simple and ovoid.

Habits - Can't fly when cold.

Larva -

Colour - Yellow to green with a darker brown head.

Body - No legs, C shaped. 5 mm long, 2 mm wide. Flattened.

Mouthparts - Chewing. Transverse action.

Antennae - 1 segment.

Legs - Has no legs or 6 legs. 5 segments.

Head - Usually a hard capsule. No ridges on forehead.

Thorax - No functional spiracle on middle segment.

Abdomen - 8-11 segments. No prolegs. Spiracles on segments 1 to 8.

Habits - Often found under leaves.

Pupa -

Biology:

Life Cycle:

Eggs laid in autumn near food source for larva and often on capeweed. Larva hatch and feed for 4 to 8 weeks on leaves then pupate. Adults feed on leaves over winter and spring and hibernate in litter or under bark over summer. They emerge to lay eggs in autumn.

Habitats:

Origin and History:

Distribution:

Significance:

This introduced weevil is a major pest of canola. It also damages a variety of vegetables and fruit crops. It seems to prefer the more succulent species and damage is often patchy or confined to the edges of crops. The adults chew the leaf edges causing deep serrations. Seedling canola may be eaten down to ground level and killed. Damaged is more severe in paddocks that have capeweed or adjoin bush.

Management and Control:

Cultivation and control of capeweed before planting helps reduce infestations.

Apply knockdown sprays as early as possible to provide a bare earth situation for as long as possible before planting. Increase seeding rates, especially on the edges of paddocks. Use Talstar for Redlegged Earth Mite control as this will provide some control of Vegetable Weevil.

Adults are difficult to kill and repeat sprays are often required. New infestations may also migrate into the crop from adjoining pasture.

Related Species:

Curculio beetle, Desiantha, Sitona weevil.

Similar Species:

Spotted Vegetable Weevil (the adult form of Desiantha) and Small Lucerne Weevil are similar to Vegetable Weevil but tend to be distributed over the whole field whereas Vegetable Weevil tends to occur on the edges or is associated with broadleaf weed patches from the previous season.

References:

CSIRO. The Insects of Australia. Melbourne University Press. (1991) p562, 682.

WADA. Insects and Allied Pests of Extensive Farming. Department of Agriculture - Western Australia Bulletin No. 4185. p98.

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.