Scientific Name: Sitophilus oryzae (Linnaeus)

Common Names: Rice Weevil, lesser grain weevil

Synonyms

Calandra oryzae

Taxonomic Position

Class: Insecta

Order: Coleoptera

Family: Dryophthoridae

Genus: Sitophilus

Species: Sitophilus oryzae

Host Range

Whole cereal grains like rice, wheat, maize, sorghum, barley and solid cereal products, some pulses and cassava are the major host.

Pest Destructive Stage

Primary Pest

Both larvae and adult can cause the damage.

Damage Symptoms

Damage is distinctive. Feeding by larvae leaves large cavities inside grains and newly emerging adults leave behind large ragged emergence holes. Adults cause further damage by feeding, mainly by attacking previously damaged grains. Weevil infestations produce a lot of heat which encourages extensive quality loss, mould growth and invites infestations of other stored grain insects.

Identification features

Eggs

The eggs are shiny, white, opaque and ovoid to pear-shaped.

Larva

The larva is white, stout and legless (apodous).

Pupa

The pupa is also white but has legs, wings, and the snout of the fully-grown weevil.

Adults

• The antennae have eight segments (elbowed antennae) and are often carried in an extended position when the insect is walking.
• Four pale reddish-brown or orange-brown circular markings on the elytra.
• Presence of wings beneath the eltyra.
• Presence of circular punctures on the prothorax.

Life Cycle

• Females generally prefer to lay eggs at the hairy end of the grains.
• 300 to 400 eggs per female.
•  Mostly, one egg per kernel.
• Peak egg laying at 14% grain moisture content at 25 – 29 ⁰C.
• Female makes a cavity and lays translucent white eggs and then plugs the hole with secreted material from ovipositor.
• Under optimum conditions eggs will hatch in 4-5 days.
• High relative humidity is preferred. Critical level is 60%.