Eight common insect pests

Rusty grain beetle

This beetle is the most serious pest of stored grain in most regions of Canada. It usually feeds on the germ, that is, the embryo, of a whole seed. Heavy infestations cause grain to spoil and heat.

Appearance and behaviour

The adult:

  • Is a flat, rectangular, shiny, reddish-brown beetle
  • Is 0.2 centimetres long
  • Has long, bead-shaped antennae that project forward in a V
  • Moves rapidly in warm grain and can fly when the air temperature is above 23°C.

Both the larvae and adults feed on the germ and on damaged kernels and wheat dust. The tiny larvae penetrate and feed on the germ of damaged kernels.

Development

Complete development from egg to adult takes about 21 days when the temperature of the grain is 31°C and the moisture content is 14.5 percent. Each female is capable of laying 200 to 500 eggs, which are deposited loosely in the cracks of the grain kernels and in grain dust.

Rusty grain beetle image

  • dorsal view of the rusty grain beetle

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Red flour beetle

This pest is found in stored grains and oilseeds on farms and in primary elevators throughout the prairie provinces and most of Canada. Despite its name, the red flour beetle is more common in elevators and farm bins than in flour mills.

Appearance and behaviour

The adult:

  • Is reddish brown
  • Is 0.4 centimetres long
  • Flies in warm weather or may be blown by the wind into farmhouses or other buildings

Larvae and adults feed on broken kernels.

Development

Complete development from egg to adult takes about 28 days under optimal conditions, that is, when the temperature of the grain is 31°C and the moisture content is 15 percent. Slower development occurs when the moisture content is as low as 8 percent.

The females lay 300 to 900 eggs loosely on top of a grain mass or in flour. Hatching produces worm-like larvae, whitish in colour with pale brown bands.

Red flour beetle image

  • dorsal view of the red flour beetle

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Confused flour beetle

Unlike the red flour beetle, the confused flour beetle is more common in flour mills than elsewhere, and the adults do not fly.

Appearance and behaviour

The adult:

  • Resembles that of the red flour beetle and is difficult to distinguish without using a microscope or magnifying glass

Larvae and adults feed on flour, feed, and other ground material.

Development

Complete development from egg to adult takes 15 to 20 days under optimal conditions, that is, when the temperature of the grain is between 32° and 35°C and and the moisture content is 14 to 15 percent.

Confused flour beetle image

  • dorsal view of the confused flour beetle

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Sawtoothed grain beetle

These beetles are more common in oats than in wheat, barley, or canola, particularly in southern Ontario and Quebec. The insects feed on dry grain, destroying the germ.

Appearance and behaviour

The adult

  • Is brown and about 0.3 centimetres long
  • Has six tooth-like projections on each side of the thorax

Development

Complete development from egg to adult takes about 22 days under optimal conditions, that is, when the temperature of the grain is 31°C to 34°C and the moisture content is 14 to 15 percent.

The female lays about 400 eggs loosely in the grain or tucked into convenient crevices. Eggs hatch in about three to five days and the young larvae begin to crawl about, feeding as they go.

Sawtoothed grain beetle image

  • Dorsal view of the sawtoothed grain beetle

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Granary weevil

This weevil is one of the most destructive pests of stored grain worldwide. It is scarce on the Prairies but occurs in Ontario. Granary weevils feed on kernels, leaving only the hulls.

Appearance and behaviour

The adult:

  • Is about 0.3 to 0.4 centimetres long
  • Cannot fly
  • When disturbed, folds its legs under its body and appears to be dead.

Development

Complete development from egg to adult takes about 25 to 35 days under optimal conditions, that is, when the temperature of the grain is 26°C to 30°C and the moisture content is 14 percent.

Weevils develop their life cycle completely inside the grain kernels. It is not until the young adult is formed that it will emerge from the kernel.

The adults have a distinctive snout, with which they bore into grain kernels. The female deposits a single egg in a hole in each kernel and then seals the opening with a gelatinous plug. The larvae feed on the endosperm and complete their development within the kernel. The pupae develop into adults that chew holes in the side of the kernels as they emerge.

Granary weevil image

  • Dorsal view of the Granary weevil

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Rice weevil

This weevil has been found in southwestern Ontario storage facilities and in some prairie elevators in recent years. A severe infestation can reduce stored grain to a mass of hulls and frass, that is, larval excrement.

Appearance and behaviour

The adult

  • Is 0.2 to 0.4 centimetres long
  • Has four distinct reddish orange spots on the wing covers which are folded over the abdomen

Adult rice weevils can fly.

Development

Complete development from egg to adult takes 28 days when the temperature of the grain is 30°C and the moisture content is 14 percent. At optimal temperatures, the life cycle may take four weeks.

Rice weevil image

  • Dorsal view of the Rice weevil

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Yellow mealworm

These insects are the largest found in stored grain. They are not common pests on farms. They infest animal feed and stored grain that is going out of condition.

Appearance and behaviour

The adult:

  • Is a black beetle about 1.5 centimetres long

The larvae:

  • Are yellow and 0.2 to 2.8 centimetres long

Yellow mealworms prefer dark, damp places in a granary or a feed bin. Because of their relatively large size, they are easily visible and often appear to be more numerous than they actually are. Their presence indicates poor storage conditions.

Development

The adult lives for several months. Under harsh conditions, the larvae may take one to two years to change into pupae.

Yellow mealworm image

  • Dorsal view of the Yellow mealworm

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Lesser grain borer

The lesser grain borer is one of the smallest -- and one of the most destructive beetles infesting grain in North America. Lesser grain borers attack most kinds of stored grains but are especially damaging to wheat, rice and corn. Both adult and larval stages cause damage. Until recently, the lesser grain borer was not considered a problem pest in Canada. There are indications, however, that its distribution is expanding, and sightings in Canada have become more frequent over the past decade. The insects have been detected on the Prairies, but they are not likely to survive a prairie winter.

Appearance and behaviour

The adult is:

  • Dark brown to black in color
  • Typically two millimetres long
  • Usually covered with a powdery flour produced as it bores through the kernels

The head of the beetle is hidden beneath the pronotum -- a shield covering the mid section of the insect.

As the name suggests, the insects bore into the kernels to feed, leaving behind a fine powder and particles of feces. They typically consume 17 to 20 percent of each kernel they damage. The rusty grain beetle, by comparison, consumes only four percent of the kernel.

Development

Complete development from egg to adult takes 25 days when the temperature of the grain is 34°C. The female lays about 300 to 400 eggs, and the larvae feed on the kernel remains left by their parents.

Lesser grain borer image

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