Sitophilus oryzae, The Rice Weevil

(Coleoptera: Curculionidae)

Synonym: Calandra oryzae.

Host: This is primarily a pest of rice but occasionally attacks wheat, corn, jowar, flour, beans, dry fruits and biscuits.

Damage: Larva as well as the adult cause damage to grains. Larvae feed inside the seed and make in hollow and exit by making a circular hole on the surface. Adults can damage several seeds by cutting an irregularly lined circular hole, through which they feed on the kernel.

Life cycle: Adults are 2-3 mm long dark brown weevils, with four faint yellow spots on the elytra. Body is punctured with minute pits. Sitophilus granarium is slightly larger in size and is found in more temperate climate. Adults do not fly but try to crawl away when disturbed. Their longevity can be up to 5 months.

Eggs are whitish, oval, 0.7 mm long. Females chew a small depression on the surface of rice grain, lay an egg in it and seal it with a gelatinous fluid for protection. Grubs make their way into seed to feed on kernel. They are plump,3-4 mm long, legless, dirty white in colour with a brownish head. Pupation takes place inside the grain. Pupa is light yellowish but later turns dark brown. Adult emerges by cutting a hole in the grain. 

Distribution: This pest is found quite abundantly throughout the warmer parts of the world, extending up to Baluchistan in Europe and Japan in the east. In Palaearctic region the species is replaced by Sitophilus granarium, which is wingless with punctuate prothorax and elytra but without four yellow spots on elytra.