Stored Grain Insects



Pea weevil

Bruchus pisorum



Adult pea weevil (Bruchus pisorum)
Courtesy of CSIRO Division of Entomology

The pea weevil (Bruchus pisorum) is a short (5 - 6 mm long), chunky, brownish beetle flecked with white, grey, and black. The white tip of the abdomen is marked with two black, oval spots. The white larvae have a brown head capsule and mouthparts. This insect is not strictly a weevil, as it does not have the typical weevil snout.


Adult pea weevil
? Agriculture Western Australia

Life cycle
The adults overwinter with the peas primarily in storage, but also in the field. The pea weevil emerges about the time the peas are blooming, feeding on flowers (pollen and petal), leaves, or pods. The elongated, yellow eggs are laid on the outside of the pods. Although one to a dozen eggs are laid per pod, only one larva develops per pea. Hatching occurs in 1 to 3 weeks and the larva burrows through into the pea, maturing in 5 to 6 weeks. Infested peas "heat," aiding in the development of the larva. Pupation takes about 2 weeks, late in the summer. There is only one generation per year. Only green growing peas are attacked. The pea weevil cannot reproduce in stored grain, but the adults can remain concealed in grain for many months.

Damage in legume seeds caused by emerging adults
? Agriculture Western Australia

If there is a heavy infestation of pea weevils the infested peas are often reduced to shells. The larval stage of the weevil tunnel and develop within the pea. They may consume nearly the entire contents as they mature. Pupation occurs in the peas and adults emerge through a neat circular hole. They will only infest ripening peas so will not infest dry peas. Infested pea seeds can lose as much as 30 per cent of their weight. Weevil infested seed may germinate if the injury is confined to the cotyledon; but these seedlings are less able to compete with weeds and other pests.

Adult pea weevil
? Agriculture Western Australia

Sprays will only kill adult weevils, not the eggs or the larvae in the pods. Crops must be inspected for pea weevil at least once a week when flowering starts. Sweeping the pea crop with a net provides greater sensitivity in detecting pea weevil than any other method yet devised, including visual inspections. If pea weevil are detected on the edges of a crop only, then a perimeter spray 50 metres wide should be adequate. More than one perimeter or whole crop spray application may be necessary. To prevent pea weevil developing in field peas grown for hay, the crop should be cut at flowering before the first pods have developed large seeds. As much of the damage occurs after harvest, all seed to be kept on the farm should be fumigated straight after harvest to prevent further pea weevil damage of infested seed. Good control of pea weevil will mean fewer weevils to infest next year's crop.