They look like harlequin bugs, probably related. Those are hard to get rid of if you get a big infestation, because they way they feed (through their built in sippy straw) makes it unlikely they ingest any meaningful amounts of insecticides that rely on being eaten. Treat them the way you do squash bugs, I guess. That means some form of hand picking and maybe get some row covers if you get rid of most of them, and the nymphs will be more suceptible to any contact poisons than the adults.

I get harlequin bugs on my horseradish in midsummer sometimes. I get rid of them by cutting off the most infested leaves and drowning the bugs in soapy water, then do follow up on all the other leaves until I don't find any more. But that might not work for all crops.

Awww man they sound bad. I've been handpicking as much as I can but cannot get to the community garden more than twice a week. They are under the one row cover I have but there are less of them there.

I am spraying at night not to burn the plants but I think they are in the soil at night and not out feeding. I see them feeding during the day.

Looks like there was a hatch and most are nymphs now so going to try to spray them again tonight. I've lost most of my uncovered brassicas to them :( all my radishes/beets/turnips as soon as they come up :(

To make things harder, they run when they see or sense me and can fly! Ugh!

I heard they don't like fish emulsion so sprayed with that too. Still there. Bought another row cover to plant under hoping it will help.