From time to time I see an outbreak of flea beetles in the garden. They are very tiny, so I see their damage first, rather than the bug itself. The damage looks like some elf using a mini shotgun went around shooting the leaves with mini buckshot. I don't go hysterical when flea beetle population explodes, but I do try to reduce their numbers. The damage they do is unsightly on mature plants but doesn't make the food inedible. But when they go after the seedlings they can stunt their growth.
Flea beetles tend to damage my seedling cabbages and broccoli. Plus they really can do a number on the beet leaves. But I found that here at my location their all time favorite is radish tops. With radishes being so quick growing and not taking up much space, radishes (and daikon) become the ideal trap crop.
I will interplant radishes with the endangered seedlings, so that if the are any flea beetles around they will munch on the radish leaves instead. By the time the radishes are ready to harvest, the other veggie plants are big enough to withstand the flea beetles.
Once the radishes get harvested, I will lay down a layer of newspaper and cover with a light mulch. Although I have no proof, I suspect that this acts as a barrier to the next hatching generation of flea beetle. The new adults can't get to the plants, thus die.
I've never had a real bad problem with flea beetles, so using the radish trap crop method works for me. I've heard of people using lint rollers to try to "roll" the underside of the leaves and capture flea beetles on the sticky tape. I've heard of people trying to use a vaccum to suck them off. I don't know if either of those two methods work. I haven't tried them. For now I'll stick with radishes.