Barley Barley Crop Icon Brassicas Brassicas Crop Icon Sugar Beet Sugar Beet Carrots Carrots Icon Leeks Leek Icon Maize Maize Icon Oilseed Oilseed Icon Onions Onions Icon Other Cereals Other Cereals Icon O R T Peas And Beans Peas and beans Icon Potatoes Potatoes Icon Salad Crops Salad Crops Icon Soft Fruits Crops Soft Fruits Icon Top Fruits Crops Top Fruits Icon Wheat Crops Wheat Icon Calendar Calendar icon Arrow Next Arrow Previous Close Checkmark

Grain weevil

1. Grain weevil adult.
2. Grain weevil damage.
3. Illustration of a grain weevil adult.


The adults are 4-5 mm long, with black heads, red thorax, blue/green metallic coloured wing cases and red/orange legs. The larvae are 'slug like' in appearance with yellow/brown humped bodies which are covered with a jelly/slimy external texture (a mixture of mucus and excreta) the purpose of which is to mimic bird or large insect droppings. The larvae are very slow moving and on close inspection 3 pairs of legs can be found near to the head.


Both the adult and the larva feed between the veins on the upper leaves of cereals and grasses leaving thin conspicuous 'windowpane' strips of eaten leaf.


From April onwards the adults emerge from their overwintering sites in search of suitable plants to feed on. In mid-summer yellow/ orange coloured eggs are laid singly or in groups of 2-3 on the upper leaf surfaces of host plants and the larvae emerge 10 days later. After approximately 3 weeks, when fully fed, the larvae move into cracks in the soil to pupate. Three weeks later the larvae emerge to feed on grasses and cereals before moving to sheltered overwintering sites later in the autumn.


Although widely seen in cereal crops, especially oats, they are very rarely of economic importance and predation keeps the population in check.


Treatment is not normally necessary in the UK, but if flag leaves are being badly grazed a suitable insecticide may be necessary. Biscaya will control cereal leaf beetle if the timing for orange wheat blossom midge coincides.


Identify Pests

Find out more information and help identify the pests found on your crops.

View now

Keep up to date with the latest from Bayer Crop Science

Sign up to our newsletter