Cereal Curculio and Desiantha
Otiorhynchus terminifera, Otiorhynchus cribricollis and Desiantha diversipes
Nocturnal and hides in the ground during the day.
Colour - Dull grey. Pale mottles.
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 in some species. Wing-span up to 200 mm. Both pairs attached to the hind body.
Mouthparts - Chewing. Pointing forward. 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 - Usually simple and ovoid.
Habits - Can't fly when cold.
Colour - white with darker orange-brown head.
Body - No legs, C shaped. 6 mm long, 2 mm wide.
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 - Live underground feeding on roots. Difficult to find.
Eggs usually laid near food source for larva in autumn. Larva hatch and feed underground on roots of pasture emerging at the break of the season. Cereals planted later are most severely damaged by well grown larva. They prefer the portion of shoot between the seed and the soil surface. In spring they pupate to become the adult weevil form. These are commonly seen in paddocks on cereal heads (and may end up in the grain sample) or under stones and debris.
Habitats:Origin and History:
The larva of these weevils attack cereal seedlings below the ground causing widespread and patchy losses of plants. Affected plants wilt and die and may be easily pulled from the ground. Partially affected plants show slow growth. Damage varies from year to year and seems to be worst on paddocks with a capeweed history after an early break to the season. The adult attacks garden plants. It seems to prefer the more succulent species. On the south coast of WA and in SA it is a major pest of cereals.
Management and Control:Insecticides alone are ineffective on the subterranean larva.
A combination of cultivations before planting, shallow planting depths, early planting, increased rates of seed to 100kg/ha and treating cereal seed with 120 mL of chlorpyrifos ec(500g/L) per 100 kg of seed are usually sufficient to keep damage to an acceptable level. Good weed control in previous crops and control of capeweed in pastures also appears beneficial. Control of summer weeds and those germinating on false breaks prevents the larva from growing to a large size when it causes most damage.
Most serious outbreaks occur on minimum tilled crops, planted late and deep after pasture in years with an early break.
Thresholds:Cereals - 10 grubs per square metre.
Inspect before planting. Dig 10 samples 32 cm by 32 cm by 10 cm deep. Sieve and count larvae which are quite small, less than 6 mm long and usually C shaped.
Related Species:Garden weevil, Vegetable weevil, Sitona weevil.
CSIRO. The Insects of Australia. Melbourne University Press. (1991) p562, 682.
Victorian Department of Agriculture. Insect Bulletins. p21.
WADA. Insects and Allied Pests of Extensive Farming. Department of Agriculture - Western Australia Bulletin No. 4185. p97.
Acknowledgments:Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.