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Read Out LoudGrain Weevil - FAQs
Published by: Fife CouncilFrequently asked questions about the Grain Weevil
Q. What do they look like?
There are 3 kinds of grain weevil found in the UK:
Grain weevils are dark brown and 3-4mm long. Rice weevils are also brown and have 4 red spots on their forewings. They are 2.5mm long. The maize weevil is the same as the rice weevil but 3.5mm long.
Q. Why are they pests?
Grain Weevils are regularly imported into the UK in grain and cereal products. Infestations can also arise from insects harbouring in the fabric of vehicles and buildings used for grain transportation and storage, or in the seams or weave of sacks. Since both adults and larvae are cold-hardy, Grain Weevils can breed readily in the UK.
Grain Weevils are one of the most important pests of farm-stored grain. They can infest otherwise undamaged grain, and will also attack hard cereal products such as macaroni and spaghetti. Fine cereal products are unsuitable for breeding purposes unless they become caked.
Rice and Maize Weevils are widely distributed in tropical and sub-tropical areas and are also frequently imported into the UK. Rice Weevils only breed in stored grain, whereas Maize Weevils can breed on maize in the field. Both species are less cold-hardy than the Grain Weevil and will not normally survive in unheated premises or in grain stored at normal temperatures.
Grain which has been damaged by Weevils can be readily recognised by the presence of large holes - these are the exit holes of the emerging adults.
There are three main ways in which Weevils damage the grain:
- the weight and quality of the grain is reduced as a result of the larvae feeding on it. Although Weevil damaged grain may still germinate, seedlings will be weak and prone to attack from moulds, bacteria and other insects
- the grain becomes tainted with white, dusty excreta which contaminates the product and makes it in-edible
- heating of the grain also occurs, which speeds up the insects’ development and makes the item liable to caking, moulding and even germination