Larger grain borer

Prostephanus truncatus (Horn)


Primary pest; Grain feeder
Order: Coleoptera
Family: Bostrichidae
Acronym: PTR


  • Adults are black or brown and cylindrical in shape, heads face down.
  • Adults are slightly larger (3 to 4 mm) than the lesser grain borer.
  • Posterior end of the elytra slope back with two strong lateral ridges with sharp edged corners.
  • Larvae are grub-like with poorly formed legs and are less mobile as they mature.


Similar species

  • Lesser grain borer (Rhyzopertha dominica)
  • Ghoon beetles (Dinoderus species) – not found in Canada

Commodities affected

  • Primarily affects maize
  • Also affects dried root crops, bamboo, rattan, cassava, wheat, sorghum, dried sweet potato
  • Will bore into, but does not feed on, cowpea, cocoa, haricot, coffee, rice

Signs of infestation

  • Characteristic damage is extensive tunneling.
  • Readily visible holes are bored in seeds.
  • Copious amounts of flour are produced.


  • Damage is distinctive and heavy.
  • Adults burrow extensively leaving tunnels and irregular shaped holes.
  • Feeding produces large quantities of flour.
  • Larval feeding and burrowing contributes further to adult damage.

How to control

Geographic range

  • Is distributed throughout tropics but not established in Canada

Where found

  • Is very tolerant of hot conditions and dry grain
  • Can establish where maize (corn) is stored on the cob and infestation can occur prior to harvest

Life history

  • Females lay eggs singly or in batches in or near food.
  • Newly hatched larvae bore into grains or feed on damaged grain and flour produced by adult feeding.
  • Larvae can successfully develop within a single seed.

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