Pea Weevil

Bruchus pisorum

Family:

Order: Coleoptera

Description:

Adult

Inactive over winter.

Colour - Dull brown with white, black or grey speckles. White tail with two oval black spots.

Body - Stout. 5 mm long, 4 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 8 mm. Both pairs attached to the hind body.

Mouthparts - Chewing. Pointing forward. Doesn't have 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 - Very small, bright orange and oval.

Habits - Can't fly when cold. Becomes active when temperature exceeds 20c.

Larva -

Colour - white with darker head.

Body - No legs, C shaped. 5 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 - Burrows into pea seed and grows inside the seed eating out the centre.

Pupa -

Biology:

Life Cycle:

Adults become active as temperatures rise above 20c and fly into the pea crop. Eggs are laid (usually singly) on the pods. Larva hatch 6 to 13 days later and burrow into the developing seed. They eat out the middle of the seed and emerge as adults. They may remain hidden in the seed for many months or find other overwintering sites. There is one generation per year. Freshly harvested seed may only show a small black sting where the minute larva has entered the seed.

Habitats:

Origin and History:

Distribution:

Significance:

This larva of this weevil eats out the centre of peas leaving a hollow shell with a large exit hole where the adult emerges. Even lightly infested seed is downgraded to feed grade. Over 80% of seed may be infested resulting in a loss of 30% of the weight of grain. Some affected seed may germinate but is low in vigour. Pea weevil is a major pest of peas and control is usually economic.

Management and Control:

Insecticides control adults but not eggs or larva. Crops need to be inspected by sweeping with a net each week from flowering to detect the adults.

Hay crops should be cut before seed development.

Stored seed should be fumigated.

Good hygiene helps reduce infestations.

Thresholds:

Start monitoring at flowering.

Peas - 2 beetles per 25 sweeps. Make sweeps about 1 m in from the edge of the crop especially near trees. A 40 m border spray is usually sufficient if clean seed has been used for planting.

Spray before Pea Weevil starts to lay eggs and before pod formation.

Check 7-10 days after spraying for new infestations. Pea Weevil is a mobile pest and new infestations may fly in.

Related Species:

Similar Species:

References:

Jacobs, W. and Renner, M. Taschenlexikon zur Biologie der Insekten. Gustav Fischer Verlag. p79pic.

WADA. Insects and Allied Pests of Extensive Farming. Department of Agriculture - Western Australia Bulletin No. 4185. p99.

Acknowledgments:

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