Identification of insect pests in stored grain

  • Colour illustration of an adult Sawtooth grain beetle
    Close-up of sawtooth grain beetle. (Image by DEGESCH America, Inc.)

Why identify stored insect grain pests?

Most insect control methods for stored grain work against all species. So you don´t need to identify the storage pests to make decisions about most control methods. But if you intend spraying grain with insecticides you may need to know which species are present if:

  • A previous application has failed and you want to know whether resistance was the reason - if more than one species survived, resistance is unlikely to be the cause.
  • You intend using a residual protectant to treat infested grain - pyrimiphos-methyl, fenitrothion and chlorpyrifos-methyl are ineffective against lesser grain borer, and pyrimiphos-methyl and fenitrothion are generally ineffective against sawtoothed grain beetle. 
  • you intend using dichlorvos to treat infested grain - if lesser grain borer is present you need to apply the higher dose rate. This then increases the withholding period before grain can be marketed from 7 days to 28 days.

Insecticide sprays are not registered for oilseeds and pulses, so identification of pests in those grains is not so important.

See Insect control in stored grain

Common species

Cereal grains

Cereal grains include wheat, barley, oats, triticale, sorghum and millets. The most common insect pests of stored cereal grains in Australia are:

  • Weevils (Sitophilus spp.). Rice weevil is the most common weevil in wheat in Australia
  • Lesser Grain Borer (Rhyzopertha dominica)
  • Rust Red Flour Beetle (Tribolium spp.)
  • Sawtooth Grain Beetle (Oryzaephilus spp.)
  • Flat Grain Beetle (Cryptolestes spp.)
  • Indian Meal Moth (Plodia interpunctella)
  • Angoumois Grain Moth (Sitotroga cerealella).

Another dozen or so beetles, psocids (booklice) and mites are sometimes present as pests in stored cereal grain.

Oilseeds include canola, linseed, safflower and sunflower. The most common pests in stored oilseeds are:

  • Flour beetles
  • Sawtoothed grain beetles
  • Moths.

See photos of insects in stored grain

Pulses

Pulses include faba beans, chickpea, cowpea, field pea, mung bean, navy bean, soybean, pigeon pea.

The most common insect pests of stored pulses are:

  • Bruchid beetles
  • Moths.

See photos of insects in stored grain

Bruchids are a major and increasing pest of pulse crops in Australia. In the northern region, Cowpea bruchid is a major problem to the mungbean industry. Adults are small, about 3.0 mm long, with a tear-shaped body. Eggs are easily visible, white and laid on surface of individual beans. Larvae develop within the seeds, from where they emerge as adults, leaving a perfectly round hole in seeds. Adults are strong fliers and lay about 100 eggs in their 10-12 day lifespan. The soybean bruchid is now becoming more widespread in the soybean industry.

See Bruchids in mungbeans and other pulse crops for more detail on bruchid pests.

Distinguishing between the common grain beetles

You can use a clean glass container as a simple test for identifying grain beetles. Put the live grain insects into a warm glass container (above 20oC so they are active, but not over 40oC or they will die).

Weevils and sawtoothed grain beetles can walk up the walls of the glass easily, but flour beetles and lesser grain borer cannot.

If you look closely at the insects walking up the glass, weevils have a curved snout at the front but sawtoothed grain beetles do not.

Distinguishing between the species that can´t walk up the glass is more difficult. Lesser grain borers are cylindrical, dark brown and usually have their head tucked under their body. Flour beetles and flat grain beetles are flatter, copper-brown, and their head usually protrudes in front of their body. Flat grain beetles are usually small, ant-like with long antennae. Flour beetles are larger with short antennae.

Most of the beetles other than the common species look something like the flour beetles, and should not be confused with the lesser grain borer if you know what the borer looks like.

See the Identification of common beetle pests of stored grain model for drawings of the common beetle pests and the steps in identifying them. 

Further information

Contact

  • Contact our Customer Service Centre
  • National Grain Storage Extension Team
    Queensland, Philip Burrill: 07 4660 3620
    Victoria, Peter Botta: 03 5761 1647
    Western Australia, Chris Newman: 08 9366 2309

Acknowledgements

  • Insect drawings used in the ´Identification of Insect pests´ sourced from Degesch America Inc.
  • Some text regarding species above was sourced from ´Insects of Stored Grain - A Pocket Reference´, David Rees (1994), Stored Grains Research Laboratory, CSIRO Division of Entomology, GPO Box 1700, Canberra, ACT, 2601, Australia.

References

  • Western Australia Department of Agriculture and Food
  • Stored grain management guide (control of stored grain insect pests).
  • Bruchids in mungbeans and other pulse crops by Hugh Brier, Pat Collins, Phil Burrill and Mike Lucy, Ken Bullen, DPI&F. 
  • ´Insects of stored grain: a pocket reference´ by David Rees (1994), CSIRO Division of Entomology. (Book available from The Librarian, Stored Grain Research Laboratory, GPO Box 1700, Canberra, ACT, 2601, Ph: 02 6246 4201, Fax: 02 6246 4202.)

Last updated 17 November 2010