What are these “eggs” on cereal heads in my field?

Quite a few people over the past week have sent in photos (as in Figure 1 below) asking what are these “eggs” on the cereal heads, and noticing that they can be quite abundant in some fields.

Parasitoid Pupal Cases

Figure 1. Pupal cases of a wasp parasitic to armyworms. Photo from Dean McCowan, Agree Ag Services.

These are not eggs, but are the pupal cases of parasitic wasps. These are being found in fields that contained armyworms, and it is likely that armyworms were hosts for the parasitoids. For some parasitoids it is common for dozens of parasitoid larvae to emerge at the same time from an individual armyworm, killing it in the process. This is because an initial egg laid in the armyworm starts dividing and can become dozens or at times hundreds of eggs, that results in multiple parasitoid larvae of the same general age feeding in the armyworm. When the parasitoids emerge form the armyworm, they all emerge at approximately the same time, and very soon after form these clusters of pupal case, which are together in a cluster on the plants. So each cluster would have been parasitoids form a single armyworm, and will result in multiple wasps looking for more caterpillars to parasitize.

Information by:  John Gavloski, Entomologist, MAFRD

This article was taken from the Manitoba Insect & Disease Update: July 14, 2015.  For the complete issue, please visit MAFRD’s website at http://www.gov.mb.ca/agriculture/crops/seasonal-reports/insect-report-archive/insect-update-2015-07-14.html





Leave a Reply

You must be logged in to post a comment.