False Wireworm or Vegetable Beetle Gonocephalum elderi, Gonocephalum macleayi
Order: - Coleoptera
Colour - Dull grey to dark brown and almost black. Often speckled or mottled.
Body - Elongated. Oval. Slightly flattened. 8mm long, 3mm 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 in some species. Wing-span up to 30mm. Both pairs attached to the hind body.
Mouthparts - Chewing. Pointing forward.
Antennae - 11 segments. Thread like.
Legs - Rear legs larger than front legs. Feet (Tarsi) simple.
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 - Usually simple and ovoid.
Habits - Can't fly when cold. Burrow in soil or live under clods and debris.
Colour - Brown with hard shiny skin.
Body - Has legs, Long and thin, cylindrical. 10mm long, 1mm wide.
Mouthparts - Chewing. Transverse action.
Antennae - 1 segment.
Legs - 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 - Feeds underground on roots.
Pupa - in soil.
Eggs usually laid near food source for larva in autumn. Larva hatch and feed underground on roots. Adults emerge in spring and survive through summer and well into winter. Found in very large numbers in heavy stubble or pasture residues where they feed on the decaying organic matter.
Origin and History:
The larva or false wireworm of some species may be minor pests of pasture, cereals and sugar cane. They rarely cause economic loss even though the may occur in prodigious numbers. The adults only eat dead or dying material and the larva feed mainly on decaying plant matter and fungi.
Management and Control:
Control is usually unnecessary and possibly counter productive.
They appear to build up in zero till and stubble retention cropping systems.
In heavy infestations a bait may be more effective than spraying. The bait is made from 40 mL chlorpyrifos (500g/L) plus 50 mL sunflower oil per 1 kg of cracked Wheat (or Sorghum). Apply 2.5 kg/ha of the bait.
Bronze Field Beetle has a larval stage that is also called the false wireworm. It tends to feed on the surface whereas the Vegetable Beetle False Wireworm tends to feed below the soil surface. The False Wireworm of the Bronze Field Beetle appears to be more difficult to control and rates of 300 mL/ha of Dominex or Fastac are required. They appear to build up in zero till and stubble retention crop systems especially on header or swath rows and can be very damaging to Lupins and Canola. Raking and/or burning the stubble provides high levels of control. In trials, raking the stubble has reduced numbers of adults by 99.9% compared to 95% control with 2 sprays after planting. Cosmos as a seed dressing and to a lesser extent Confidor have shown promise in trial work (P. Michael, 1999).
To reduce the impact of Bronze Field Beetle and it larvae in Canola and Lupin paddocks;
1) reduce the trash level,
2) lay a carpet square on the ground in autumn to determine the level of infestation,
3) if it is high, treat seed with Cosmos, Confidor or Lorsban
4) increase crop seeding rate
5) Spray with 300 mL/ha Dominex 100 (or equivalent synthetic pyrethroid) around emergence of the crop, if damage is still occurring. Repeat in 10-14 days if necessary.
CSIRO. The Insects of Australia. Melbourne University Press. (1991) p562, 666pic, 667.
WADA. Insects and Allied Pests of Extensive Farming. Department of Agriculture - Western Australia Bulletin No. 4185. p43.
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