Granary weevil
Sitophilus granarius (L.)

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

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

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 15oC, but development is prolonged.
  • Optimum development takes place between 26 to 30oC at a relative humidity of 70%.

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