If each plant has three of these bugs how many are finding mates?
What are they? Invasive beetles? Each plant has 1 or more looking for a mate. Will neem oil be enough to control them? I want you to tell me they're beneficial, as they are moving through my ornamental shrub and flower beds.
The insects in your images have several different common names, among them Hedge-nettle Stink Bug and Happy Bespectacled Stink Bug. (The Latin name is Cosmopepla conspicillaris.) The paired set are a male and female.
Little information is available about them. Thus, I'm unable to suggest how many might result from mating.
During my research, I located one sourcewhere they are listed as potential plant pests. [On page102 in the book "Insects of the Pacific Northwest"] Even so, we seldom receive questions or complaints about them.
See "Stink Bugs of Oregon" for brief text plus images of their eggs and younger stages - http://www.oregon.gov/ODA/shared/Documents/Publications/IPPM/StinkBugGuide.pdf.
If you have only a few, flick them into soapy water where they will drown.
Thanks, Jean! There must be 300 or more and as long as they're not a destructive beetle but a stink bug, I have no worries.