Rice weevil

Rice weevil

Sitophilus oryzae (Linnaeus) Coleoptera: Curculionidae

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

Pest status:

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

Identification:

Adult is 2–2.5 mm in length, head with a snout, varies from reddish brown to nearly black and usually marked on the back with four light reddish or yellowish spots and has fully developed wings beneath the wing covers.
May be confused with: Granary weevil, maize weevil.

Host range:

Major pest of whole cereal grain including wheat, rice and sorghum, but also infests cereal products such as pasta.

Life cycle:

Adult weevils can fly and live 4–5 months and 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. On emergence, the adult may spend a few days inside the cavity and finally chews its
way out. The total development period from egg to adult takes about 25 days at optimal conditions of 30°C and 70% relative humidity but this period is greatly prolonged during cold weather. The maximum population growth rate
per month is 25 times.

Risk period:

All year

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.

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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.

Action level:

When detected.

Chemical control:

Fumigation in sealed storage, grain protectants.

Cultural control:

Good hygiene with storage and handling equipment should minimise infestations.

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