Could you give more info on the bugs? Are they beetles, caterpillars, wingless, etc.? How long and wide? Are they shield-shaped, oval, like a speck, do they have long or short legs, what is the pattern of the colors (stripes, spots, half-and-half)? This would really help.
Holes in the leaves on brassicas are often from slugs, which can be killed by using diatomaceous earth sprinkled around the ground in a ring at the base of each plant. Are you sure it is the bugs that are causing the damage (some bugs congregate to drink droplets of water or to mate on cool leaves that transpire alot of water)? If they are the guilty party, try an insecticidal soap. I have used Safer's, with success against many pests. It is an organic fomualtion.