Lots of small irregular holes in the leaves of seedlings and young transplants are the first clue that flea beetles may be dining in your garden.
Some species of flea beetles feed on a variety of plants while others just attack members of one family. These tiny dark beetles can be difficult to see and jump out of sight when disturbed.
The adults overwinter in leaf litter, producing just one generation in the north, but two or more in milder climates. Remove plant debris in fall to eliminate their winter homes.
Cover seeded rows and transplants with floating row covers at planting.
And remove weeds in and around the garden that can attract these pests.
A bit more information: Try trapping flea beetles with a shield or box coated with a sticky substance like tanglefoot. Pass it over the plants and catch the insects as they jump.