Answer: Cucumber beetles are yellowish green, with black spots or stripes. Larvae feed on the roots, they pupate, finally becoming beetles, which then chew the plant parts and are most destructive as well as visible. These adults overwinter in debris in your garden.
Now, how to control them. Since the adults overwinter in garden debris and lay the eggs in the spring when the soil warms up, your "modus operandi" should be to clean up that debris thoroughly. It's best to do this in the fall, to remove overwintering sites, but at the very least, do this FIRST thing in the spring when you get out into your garden. Do NOT put the debris in your compost!
Next, never plant those squash or cucumbers in the same garden spot year after year. You need to rotate these crops.
Try covering your plants from germination until bloom time with floating row covers secured all around so the adults can't fly in. (You'll need to check periodically to be sure you haven't trapped any beetles underneath.) Remove the cover when the plants flower, so the bees can pollinate them. By then, the plants should be large enough to withstand some feeding by the beetles. Also, a thick straw mulch around plants can deter beetles from laying their eggs there.
If you find yourself with an infestation of adult beetles, use a pyrethrum-based spray. Use this sparingly, since it can harm beneficial and pollinating insects.
Q&A Library Searching Tips