Grain Weevils

Latin Name: Sitophilus granarius

Months of Activity: January - December

The grain weevil is the main stored grain pest of countries with a temperate climate. Although some damage is caused by the adult, most is caused by the larvae: newly emerged adults leave a characteristic emergence hole in the grain.

Prefers wheat and rye, but will also infest other cereals such as corn, barley, millet, rice, buckwheat, and oats. The weevil will also occasionally eat flour, whole meal or pasta.

Appearance

• An adult grain weevil will grow to between 2-4mm in length. They are black / brown in colour and have oval indentations in the thorax. The neck shield has depressed markings and is almost as long as the longitudinally-grooved wing covers.
• The grain weevil larva is usually hidden within grain where it pupates. It is legless and emerges in a red / brown colour shortly after hatching.

Lifecycle

The female grain weevil bores a hole into a kernel of grain and lays an egg, sealing the opening with gelatinous material. Full development of the weevil takes place within the kernel of grain and is not discernible from the outside. The development phase of the grain weevil depends on temperature, normally taking about 8-16 weeks. Females can lay more than 200 eggs under favourable conditions.

The entire life cycle from egg to adult may be as short as one month during the summer or as long as 5 months during the winter, being very dependent upon the temperature. There are usually 4 generations per year with adults living between 7-8 months.

Pest Control

To eradicate a small scale grain weevil infestation, you should follow the guidelines below. If your infestation is on a larger scale, then you should contact your local pest control provider for assistance.

• Remove all dishes and food from cabinets.
• The beetles need to be killed before you throw out the foodstuffs as they will reinfest.
• Foodstuffs stored in paper, waxed paper, metal and some glass containers can go in the oven for 1 hour at 135 degrees Fahrenheit or in the freezer at 0 degrees fahrenheit for 6 days to kill all stages of the beetle.
• Store food in containers with tight fitting lids.

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