Granary weevil

Classification

Primary pest; grain feeder
Order: Coleoptera
Family: Curculionidae
Acronym: SGR

Description

• Adults are uniformly coloured dark brown beetles, about 5 mm in length.
• Adults are unable to fly.
• Larvae are white, legless grubs that develop within the kernel and, as such, will not be detected in sieve samples or Berlese funnel samples.

Similar species

• Rice weevil (Sitophilus oryzae)
• Maize weevil (Sitophilus zeamais)

Commodities affected

• All small grains (notably wheat, corn, rye, oats, barley, sorghum)
• Sometimes found in pasta, flour, meal and other cereals but is generally unable to breed in this environment

Signs of infestation

• Increased moisture levels and heating on the surface
• Seeds with round holes formed by exiting adults

Damage

• Adults feed on whole seeds or flour.
• Larvae develop inside seeds or pieces of seed or cereal products large enough to house larvae, but will not develop in flour unless it has been compacted.
• Weevils can achieve almost complete destruction at high densities.
• Feeding contributes to heating and infested grain is often damp due to moisture added by the insects’ metabolic processes.

How to control

• Control grain insect pests

Geographic range

• Is distributed worldwide
• In Canada, it is found in British Columbia, Alberta, Saskatchewan, Manitoba and is common in farm storage in southern Ontario.

Where found

• Only occurs where grain is stored; does not breed in field

Life history

• Females lay 150 eggs over their 7- to 8-month lifespan.
• Females individually lay eggs within kernels.
• Adults emerge from a large, oblong hole in kernel, compared to a smaller and rounder hole for rice weevil.
• Infestation can establish at temperatures as low as 15^oC, but development is prolonged.
• Optimum development takes place between 26^oC to 30^oC at a relative humidity of 70%.