Pests of stored grain
by Vincent Hervet and
Grain stored in bins can be infested with seed feeding
insects. To maintain high quality grain, there is zero tolerance for live
insects in grain sold into the commercial grain handling system.
There are over a 100 different stored grain insects in
Canada, but only three are commonly found in grain bins on farms: the rusty
grain beetle, the red flour beetle, and the foreign grain beetle.
The rusty grain beetle and the red flour beetle feed on
grain, particularly damaged grain. The foreign grain beetle is a fungus feeder,
and its presence in bins is associated with moldy grain. The small size and
flat shape of these beetles enable them to crawl through gaps between kernels,
making them difficult to detect. The pictures below display beetles on kernels
of wheat for size comparison.
According to the Canadian Grain Commission, 90% of the
detections in terminal elevators are the rusty grain beetle, 5% are the red
flour beetle, and the reminder various other insects.
High fertility and a rapid development rate enables this insect
to quickly increase its numbers, up to 60 times per month under ideal
conditions. This allows it to rapidly increase in the warm grain after harvest.
Adults can live for over a year and are often able to survive the winter in the
centre of unaerated bins.
Red flour beetles also develop rapidly, but die during the
augering of grain and are less cold tolerant than the rusty grain beetle.
Infestations of this insects can be controlled by lowering the grain
temperature soon after harvest with aeration. The development rate of all
species increases with higher grain temperatures and moisture contents. Their
development and reproduction ceases below 18 °C. Fumigation with phosphine is
another control method, and requires licensed operators for application.
In the absence of – or with too little – air drying, the
natural cycle of air in grain bins makes moisture migrate to the centre and top
of bins (see diagram below). This can create a hot spot where insects and molds
thrive. Use aeration to cool and dry the grain. Further information on the
prevention of spoilage of grain in bins can be found at: https://www.grainscanada.gc.ca/en/grain-quality/
Created November 21, 2019 | Category: Bug of the Month