Grey-banded leaf weevil

Consultant, Tim Condon (Delta Agribusiness), reports finding very high numbers of small grubs feeding on marshmallow weed in paddocks throughout the South West Slopes district of New South Wales. These have been identified as larvae of the grey-banded leaf weevil (Ethemaia sellata). Tim says they have been noticed over the past few years however this year they appear to be present in significantly higher numbers. Some marshmallow plants have been completely defoliated, including some damage to the stems, however no crops appear to be coming under attack at this stage.

Grey-banded leaf weevil larvae have also been identified for agronomist, Elissa Strong (AGnVET Services), who reports finding them in various paddocks around Forbes, in the Central West Slopes & Plains district of New South Wales. Elissa says they appear to be widespread around the district and in all cases they have been found associated with marshmallow weed. As yet, no damage has been detected on any adjacent cereal crops. 

Little is known about the feeding ecology of grey-banded leaf weevils. Adults are known to attack several winter crops including canola and lupins, and may also be a grain contaminant at harvest. It is thought that they may feed preferentially on malvaceous weeds (such as marshmallow weed) and some ornamental plants, and these could be the source of infestations in crops. This species has been recorded as common in gardens, and both adults and larvae are known to attack several ground vegetables.

Larvae are yellow to green in colour with a light green to brown head capsule, and are often confused with vegetable weevil larvae, which are similar in size and colour. They are legless and grow to approximately 5-8 mm long. Adult weevils are approximately 8 mm long, grey in colour with distinctive raised markings (bumps) and a white area on the bottom covering approximately 1/4 of the wing covers (elytra). Adults are thought to be flightless. Eggs are laid on plant leaves and pupation occurs in the soil.

Crops should be monitored closely, particularly near fence-lines, as adults tend to move into crops from host weeds and scrub. There are no insecticides currently registered to control grey-banded leaf weevils. However, when synthetic pyrethroids have been used at 400mL/ha against other pests, they are reported to provide adequate control of grey-banded leaf weevil. Previous reports also suggest that canola paddocks sown with insecticide-treated seed experience less feeding damage from weevils.

Click here for images of the grey-banded leaf weevil.