Monitoring stored grain for insect pest infestations
One of the best ways to prevent insect infestations is to monitor bin-stored grain every 2 weeks to detect early signs of deterioration or infestation. This section explains several devices you can use to sample grain and check for insects.
Trapping to determine the presence of insect pests in stored grains is a simple and cost-effective way to monitor for infestations and identify insect pests so that you can make decisions about insect control.
How to use pit-fall traps
Probe pit-fall traps are one of a variety of traps that have been developed for use in stored food. The photo shows two kinds of pit-fall traps:
- A pheromone-baited pit-fall trap (top left corner)
- Open trap (left) and closed trap (right). The trap is closed when in use.
- A pheromone-baited probe pit-fall trap (bottom right corner)
- Intact trap with a string attached to it and the internal components of the trap
Push probe pit-fall traps in the grain at the top of the pile, near the centre. When the grain becomes cooler than ambient conditions, insects tend to migrate to this area of the bulk.
Grain that is in storage should be level, and probe pit-fall traps should be placed in the grain as early as possible. Insert them so that the upper portion of the trap is no more than a few centimetres below the surface. Attach brightly colored twine or rope to the trap so that it can be readily retrieved.
Remove the trap every 10 to 14 days to inspect it for insects. Continue doing this until the grain temperature is below 18°C. After this, monthly monitoring is sufficient. If insects are discovered, use treatments such as aeration; moving and turning the grain; or fumigation or contact insecticide application.
Use the following number of traps for different bin sizes:
- 1 to 2 traps for bins that hold less than 25 tonnes (900 bushels)
- 2 to 3 traps for bins that hold 25 to 50 tonnes (900 to 1800 bushels)
- 3 to 5 traps for bins that hold more than 50 tonnes (1800 bushels). Place the first trap in the centre and insert the remaining traps in a radius approximately one metre from the centre.
Probe sampling and sieves
If it is not possible to install and monitor traps, for example, when grain is stored in welded steel hopper bins with limited access, sampling, examining and sieving are also effective ways to monitor grain.
A torpedo-type probe is used to sample grain at various depths. To sample grain,
- Insert the probe so that the upper portion is 10 to 15 centimetres below the surface.
- Probe the grain at the same location and depth until approximately 500 grams are obtained.
- Multiple samples should be taken if possible.
Grain trier probes can also be used to sample grain. To use them properly, however, you need to have complete access to the grain bulk.
- Insert the probe so that all sections of the trier are immersed into the grain.
- Open the gate on the probe for sufficient time to allow the trier to fill.
- Cose the gate on the probe, remove from grain and inspect the sample.
To inspect the grain use the following sizes of sieves:
- No. 10 sieve (2 millimetre aperture) for wheat and barley
- No. 20 sieve (0.85 millimetre aperture) for canola
- Shake the samples in the sieve thoroughly (20 times minimum)
Examine both the grain remaining in the sieve and the material in the collection pan. Many stored-product insect pests are very small and can often be found in the removed material. Spread the removed material on a light-colored surface and use a strong light (60 to 100-watt bulb) to examine it. The heat and light from the bulb will cause any live insects to move, making detection easier.
Look at the sieved grain for kernel damage such as concave indentations in the endosperm or complete removal of the germ, both of which may indicate an insect infestation. Damage caused by the rusty grain beetle, for example, can be identified by the small exit holes the beetle leaves in the germ. If damage is detected but no insects are found it is advisable to take another sample to see if insects can be found.
If you suspect that bin-stored grain is infested and you want verification, send a sample of the grain to one of the Canadian Grain Commission's entomology labs for analysis. The entomology labs use a procedure called Berlese funnel extraction to examine the sample for presence of insects.
Berlese funnel extraction works in the following way:
- A 60-watt light bulb, housed in a reflective shade, is suspended above a funnel containing approximately 1,000 grams of suspect grain.
- A collecting jar is placed under the funnel.
- Water in the jar prevents insects from escaping.
- Over several hours, light and heat generated from the bulb and reflector cause stored-product insect pests to move through the grain into the collecting jar where they can be identified.
Grain run through a Carter dockage tester, the insects will be collected in the aspirator pan near the top of the machine or the pan containing the smallest sortings.
If insects are discovered
Upon insect discovery, but before taking remedial action, it is important to determine which species of insect pests are present in grain. Many insects appear similar but have different behavior and status as pests. Their presence may indicate different conditions. The insects in the examples below look similar to each other.
Secondary insect (Fungal feeder)
The presence of insects like foreign grain beetles may indicate that fungus is developing. Simple treatment methods such as aeration may be applied to prevent further damage.
Primary insect (grain feeder)
The presence of insects like rusty grain beetles indicates direct damage to grain kernels. In this case, insecticides or other treatments may be required to control the infestation and prevent further damage.
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