Rice weevil (Sitophilus oryzae)

Type of pest: Primary pest.

Distribution: Worldwide

Identification: Adults are 3 – 4 mm, dark brown to black, and the elytra each have two dull orange spots, while flight wings (under elytra) are present, the thorax has circular shaped punctures, and the club-shaped antennae are kinked halfway. The pronotum is barely shorter than the elytra. Larvae: apodus is white and legless.

Similar species: Sitophilus granaries and Sitophilus zeamais. These species are identical externally and can only be distinguished by examination of genitalia.

Life cycle: Optimal conditions are 25 days at 30 ºC, 70% r.h. Female rice weevils lay between 300 to 400 eggs and 2-3 eggs in the grain. Eggs are laid singly in a prepared hole in the grain and then covered with waxy plug. The larvae are immobile, and develop concealed within a single grain. The larva eats the grain empty and pupates inside the shell of the grain. Emergence holes of the rice weevil are smaller than those of the granary weevil, and tend to be smooth and round. Adults leave the ragged hole in the grain on emergence, are long-lived, feed and cannot fly. The adult rice weevil lives at a temperature of 28 º C for about 3 months, and at 20 º C they live 5-7 months. When the temperature is lower than 13 º C, development is stopped.

Commodities infested: Cereal grains and solid cereal products e.g. pasta. Sitophilus oryzae also infests stored pulses. There is generally no external evidence that the larvae have been eating until when the adult weevil chews through the seed coat and emerges. The adults can feign death by drawing up their legs close to the body, falling, and remaining immobile when disturbed. Due to many droppings of rice weevils the products can be stale and of bad quality. Both the beetle and the larva produce damage to the products. If large numbers of rice weevils increase the temperature of the stock by breeding in the excrement, this may cause mold. They will not feed on furniture, the house structure or other items. The harm they cause is destruction of the seeds they infest.

Preventive measures include: cool and dry storage areas, clean empty spaces.

Treatment: Controlled Atmosphere for infestation in product
Treatment: Heat Treatment for infestation in buildings

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