Hi, Marianne.  Thanks for reaching out to the Ask Extension Helpline.  It seems that you have the four-lined plant bug on your oregano.  This is a common bug where both the adults (greenish-yellow with four black stripes) and the nymphs (red) feed on leaves, leaving dark, round sunken spots.  They like mints, oregano and other herbs, as well as a surprising range of perennials and shrubs.  Although they rarely seriously damage plants, they can cause wilting, brown leaves and disfigurement.  Luckily, there is only one generation per year.

For management, if there are not too many bugs, the standard practice is to ignore them.  They will be gone around mid-summer.  In the case of your oregano, I would cut off the upper parts of the affected stems now and wait for new growth below.  In the fall, cut stems all the way to the ground and discard/destroy them, as the bugs insert their eggs into the stalks to overwinter.  By removing the stalks you are removing the next generation!  (I cut my oregano back drastically last fall, and this year there is minimal damage- yay!)

Here is a link to good basic info, including management choices: https://extension.umn.edu/yard-and-garden-insects/four-lined-plant-bugs

For a more detailed scientific description, try this: https://entnemdept.ufl.edu/creatures/veg/leaf/Poecilocapsus_lineatus.htm

I hope this helps!






 

You're welcome!  Good luck.