Is this bug harmful to my plant?

Asked August 13, 2015, 7:44 PM EDT

I found the Oncopeltus fasciatus on my milkweed plant that I have in my butterfly garden. It's eggs seem to be coating quite a lot of the plant. I'm worried that it will overtake the plant and kill it. I'm also worried that it will drive the bees that have already shown up, as well as the butterflies I'm hoping to attract. Should I be worried about this? Is this bug harmful to the plant, should I get rid of the bug? If I need to get rid of it how would I do that without killing the plant, bees and butterflies in the process?

Dodge County Wisconsin milkweed bug insect id

4 Responses

Your insect is commonly known as the milkweed bug, Oncopeltus fasciatus. This insect is more of a nuisance than a pest and one strategy is to simply ignore it. This insect eats the seeds of the plant, so it is a late season insect and doesn't harm the plant. If you choose this option, be sure to practice good sanitation practices this autumn/early winter.
If you choose to attack the insects, insecticidal soap will work fine.

They seem to have gone for now. I would like to harvest the seeds myself in order to have more plants later on. I would therefore be interested in the insecticidal soap you referred to, but I have questions about that. Is the soap something that will be harmful to the bees, caterpillars/butterflies that visit the plant? Also do you have an example of that soap (name/brand) that I could use to help locate it in a store?

Also if I choose to ignore them as I have so far what sanitation practices are you referring to?

Insecticidal soap is available in most garden centers, farm stores, hardware stores, and probably most large home stores. There are several brands available (Conserve, Safer, etc.), however, the active ingredient in all of them is 'potassium salts of fatty acids'..
You should attempt to spray the soap directly on the bugs as you see them. The residual will not harm bees or other pollinators.
Milkweed bugs over-winter in garden debris, so the sanitation practices include raking up all plant material or other debris and disposing of it.