Wheat stem sawfly
Exotic to Australia
Features: two species of exotic wasps that damage wheat
and other cereal crops
Where they’re from: The European wheat stem sawfly
occurs in Europe, parts of Asia, Canada and North America
The wheat stem sawfly occurs in in western parts of the
United States and Canada, Kazakhstan
How it spreads: Importation of infested crops, straw, straw
contaminated machinery; local spread by flying
At risk: Grains, grasses
Wheat stem sawfly larvae live and feed inside wheat stems
and can cause huge amounts of damage to cereal crops.
Frank Peairs, Bugwood.org
Keep it out
European wheat stem sawfly (Cephus pygmeus) and the closely related wheat stem sawfly (C. cinctus) are types of wasps that cause significant damage to winter cereals such as wheat, oats, barley and rye in many parts of the world.
Both species lay eggs in the stems of grasses and grain crops. The larvae (grubs) feed within the stems, filling them with frass (droppings), damaging the plant by cutting off nutrient flow. When the larvae finish feeding they cut the stems off near the ground.
In fields of cereal crops the insect causes big losses. As well as cut stems, damage from feeding causes lodging, which is when wheat stems collapse near to the ground. Lodging makes it difficult to harvest the grains from the flattened crop as well as making the crop more susceptible to other pests and diseases.
Overseas, sawflies are spread as larvae in the stems of infected crops. Cereal straw that is baled as hay or carried on machinery can spread the pest over long distances. Adults can spread locally by flying.
In the southern prairies of Canada and the adjoining parts of the United States, the wheat stem sawfly is a major pest of wheat in spring and winter. Crop losses of up to 80 per cent have been reported. It is feared that the pest would establish and spread and cause similar damage here if it makes it through border controls.
To keep wheat stem sawflies out of Australia, never ignore Australia’s strict biosecurity rules.
Import shipments may need to be treated and certified, so before you import, check our Biosecurity Import Conditions system (BICON).
What to look for
- The European wheat stem sawfly is a black and yellow wasp about 8-10 mm as an adult. The wheat stem sawfly is very similar, though it can grow a little larger at 7-12 mm.
- Lodging (fallen stems) and cleanly cut stems in fields of cereals.
- Grubs and frass (droppings produced by the larvae) in stems.
Where to look
Illegal importation of infested plants and straw is the most likely way that the pest could enter Australia.
- Check your property frequently for the presence of new pests and closely examine the cause of any lodging in crops, especially where there are cleanly cut stems.
- Make sure you are familiar with the symptoms of common pests so you can tell if you see something different.
- Early in the season, look for small yellow and black wasps on wheat plants along the edges of the field.
- Resting sawflies will sit on the stem facing the ground. Later, cut stems open to look for the white, S-shaped larvae or the sawdust-like material resulting from their feeding.
Look for signs of wheat stem sawfly in:
What to do
If you think you’ve found wheat stem sawflies:
- take a photo
- contain the bug without disturbing it (this may be as simple as closing the doors on a shipping container or preventing access to a field)
- collect samples, if it is possible to do so without disturbing the insects.