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Stored grain insects

Now that harvest is underway in many regions, it is timely to consider how to best manage grain quality post-harvest. Harvested grain is at its highest quality when it is first loaded into storage. If the storage environment is not managed correctly, then quality will steadily deteriorate. Grain storage expert, Peter Botta (PCB Consulting), says three key factors (farm hygiene, aeration cooling and storage choice) can provide significant benefits for both grain quality and control of storage pests.

There are many damaging insect pests of stored grain and phosphine fumigation is one of the most commonly used techniques for protecting grain. Unfortunately the widespread use of phosphine has lead to the development of resistance in several insect pests of stored grain, including the lesser grain borer (Rhyzopertha dominica), the saw toothed grain beetle (Oryzaephilus surinamensis), the flat grain beetle (Cryptolestes spp.) and the rust red flour beetle (Tribolium castaneum). There are many other beetles, moths and mites that can also be pests of stored grain. Correct insect identification will allow for more targeted control options, and minimise the likelihood of control failures due to resistance.

The best approach to manage chemical resistance is to ensure phosphine is only used when necessary and fumigation takes place in gas-tight storages. Phosphine should be held at lethal concentrations for 7-10 days to ensure effective control of all insect life stages. The following steps are recommended in order to minimise problems that can reduce grain quality in storage:

  • Clean up grain residues and spillages in and around empty storage facilities and machinery.
  • Ensure insect pests are not carried onto your property on farm machinery.
  • Silos that will be fumigated should have their seals checked prior to filling to ensure they are gas-tight.
  • Install aeration cooling fans and aeration controllers.
  • Monitor grain monthly for insects, grain temperature and moisture.
  • Grain that is to be stored for more than 6 weeks should generally be treated with an insecticide.

Grain hygiene is also a critical factor. Grain residues in or around storages, or older grain stocks held over from last season provide ideal breeding sites for insects. As little as one bag of infested grain can produce more than one million insects during a year, which can travel to other grain storages where they will start new infestations. Successful grain hygiene involves the removal of all waste grain from storages and equipment including headers, augers, storage facilities and old grain bags.

For further information on grain storage pests, including monitoring and management refer to GRDC FactSheet - Stored Grains Pests, the GRDC Grain storage facilities booklet or visit

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