Wheat head armyworm doesn’t only affect wheat; it can also affect barley, rye, oats, native and forage grasses like timothy, and even gets into wild oats — it’s got a wide host range to say the least.
The impact of wheat head armyworm isn’t well documented, and part of the problem with researching them is that they’re hard to find; they pop up where you don’t expect them, says Tyler Wist, entomologist with AAFC Saskatoon. The research dollars get allocated, but you can’t get wheat head armyworm into a colony to study them.
The common name armyworm can be confused with all the other types of armyworms out there (which is why we rely on the latin names of insects to properly identify them) but Wist says that the best way to identify them is by situation.
“If you’re in a wheat field and you’ve got a kind of tan coloured caterpillar sitting on your wheat heads, it’s pretty likely that it’s a wheat head armyworm, because it’s in wheat and it’s sitting on the head of the wheat,” says Wist. Not a lot of other caterpillars would sit up high on the wheat head like that.
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As for what predates on wheat head armyworm? Wist says that in some previous research by Dan Johnson, who’s now at University of Lethbridge, a cotton-ball looking cluster of pupae on the heads and awns of wheat and barley were identified. Those pupae have been identified as the genus Cotesia, with a few different species, and what’s really interesting about these species, is that they’re typically only female.
“Every single one of those insects that come out of the pupae is ready to go out and find another host, so another caterpillar host to sting and lay and egg into,” says Wist. The single egg that’s laid into the caterpillar body, splits into 20 to 30 little genetically identical larvae that hang around for a while, then chew threw the body of the wheat head armyworm caterpillar body, and emerge en masse.
It sounds like something from a horror film (Alien franchise, anyone?) but, hey, nature is a great place for sci-fi inspiration. In short, Wist says that wheat head armyworm might be kept in check effectively by the as-of-yet unidentified Cotesia species offspring.
Wist’s number one suggestion for protecting these parasitoids that control wheat head armyworm? Make sure you’re at economic threshold before taking any in-field action to control the armyworm, and the Cotesia species will take care of the issue.
Wist concludes that although the relationship looks promising, more research will need to be done.