Rice weevil
Sitophilus oryzae (L.)

Order: Coleoptera
Family: Curculionidae
Acronym: SOR

Ecology

The rice weevil is distributed in tropical environments. However, it is becoming established in temperate environments due to changes in the transportation and storage of rice. In Canada, it is reported in British Columbia, Alberta, Saskatchewan, Ontario, Quebec, New Brunswick and Newfoundland. The rice weevil feeds on rice, wheat, barley and on other raw or processed cereals such as pasta. It prefers warehouse or storage conditions. The rice weevil is closely related to the maize weevil.

Damage

The rice weevil causes damage similar to that of the maize weevil and the granary weevil. The larva feeds within the kernel and consumes the endosperm. The adult leaves a large, ragged exit hole in the kernel and feeds on damaged kernels.

The rice weevil adult gathers and reproduces in stored grains. This produces heat and moisture which can lead to mould development and invasion by other insect species.

Life history

The adult is small; it is 2.5 to 4 mm long. It is dark brown. The adult has a long, distinctive snout and elbowed antennae. It has 4 distinct reddish patches on the elytra. The adult can fly.

Breeding conditions are temperatures between 15°C and 34°C and a relative humidity at 40%.

The female lays most eggs within the first 4 weeks after it emerges. It chews a small hole in the grain kernel to lay one egg and covers the hole with a waxy secretion. The female lays approximately 150 eggs in its lifetime.

The larva develops in the kernel. The larva is white, grub-like and legless. Under optimal temperature conditions between 27°C and 31°C, the rice weevil’s life cycle is complete in 5 to 8 weeks. The shortest development time is 25 days at 30°C and 70% relative humidity. Development stops if the temperature falls below 17°C. he larva pupates in the kernel.

Once the adult emerges from the kernel, it mates and lays eggs immediately. Adults live from 4 to 12 months.

Control

An infestation of rice weevils can be difficult to detect because the insects behave in an aggregative fashion and the immature stage occurs only in the kernel.

To prevent an infestation, routinely monitor for signs of an infestation. Clean bins regularly and treat them with a registered insecticide. Properly dispose of any grain debris found outside of the storage area.

To control an established infestation, fumigate, apply insecticide and lower the temperature of the commodity to at least -5°C for a minimum of 12 weeks.

Images

Rice weevil: egg, larva, pupa and adult.

Adult rice weevils.