Rice weevil

Close-up photograph of a rice weevil preparing to lay its eggs in stored grain
Rice weevil preparing to lay eggs on grain
© State of Queensland

Scientific name

Sitophilus oryzae

Description

Adult is 3-4 mm in length with a snout. Varies from reddish-brown to nearly black with four light reddish or yellowish spots on its back.

Similar species

Granary weevils, maize weevils.

Distribution

Cosmopolitan, established in all regions except the coolest temperate regions. In Australia, this pest occurs in all grain-growing regions.

Pest status

Major, widespread, regular. A primary pest of stored grain.

Host range

A major pest of whole cereal grains but also infests cereal products such as pasta.

Damage

Larval feeding leaves large cavities inside grain and emerging adults leave large emergence holes. Adults feed on the damaged grains and large numbers produce heat and moisture, encouraging mould growth and mites, both of which reduce quality.

Risk period

All year.

Life cycle

Adult weevils live 2-4 months, do not readily fly but will climb vertical surfaces. Each female lays 300-400 eggs during its lifetime. Eggs are laid singly in holes dug in grain and covered with a waxy plug by the female; larva grows inside the grain, excavating a cavity as it grows and pupates inside it.

The total development from egg to adult takes about 25 days at optimal conditions of 30ºC and 70% relative humidity but this period is greatly prolonged during cold weather.

Monitoring

Commercially available pitfall and probe traps can either be placed on the grain surface or inserted into the grain bulk. Acoustic detectors and X-ray photography are also available commercially to monitor the developing stages feeding inside the grain.

Control

Chemical control
Fumigation in sealed storage, grain protectants. For current chemical control options see Pest Genie, Australian Pesticides and Veterinary Medicines Authority (APVMA) or Infopest.

Cultural control
Good hygiene with storage and handling equipment should minimise infections.

Further information

Last updated 10 March 2011