Saltmarsh Caterpillar or Woolly Bear
By Hector Carcamo and Vincent Hervet
I heard another report of damage to canola on Twitter #abbugchat recently in addition to a direct query Vince and I handled previously. It's important to note that people see damage then find these caterpillars because they are easy to spot. However, their numbers are usually low and they do not cause severe damage. More likely cutworms cause the damage by feeding below ground. They are harder to spot. So don't blame the innocent!
You can find information in Field Crop and Forage Pests and their Natural Enemies in Western Canada guide on page 82.
While reading about Woolly Bears, I read there are other Woolly Bear species in the southern USA that feed on leaves loaded with alkaloids which help them get rid of parasitoids inside their bodies: this is a case of self-medication among insects! Bugs are cool, eh?
This is a very interesting topic! When I heard of the presence of Saltmarsh caterpillars in fields displaying economic level damages, my first thought was that their presence must be coincidental because they are not known to reach economic levels on the Canadian prairies.
Cutworms must be the more likely culprits, but I have doubts now. This is the third such report in southern Alberta this year. This is getting peculiar. These are very large caterpillars and fast crawlers. Just a few of these caterpillars in a field where seedlings are starting to grow could potentially be devastating. Saltmarsh caterpillars do reach economic levels in the States. With global warming, it may just be a matter of time for them to become a problem here. I asked the agronomist who contacted Héctor to scout for cutworms but haven't heard back. To really solve this question, I think we need to find cutworms at economic levels or fail to find them.