Are your cucumbers, squash, melons or zuchnini getting eaten? Look for cucumber bettles (yellow with stripes or spots). The adults eat the leaves and they aren’t too bad, but the main problem is that they lay their eggs near the roots of the plants and then the larve suck nutrients from the plant. There isn’t really an effective organic way to get rid of them, except to keep the adults from laying their eggs, as best you can.
Update: You can also try using diatomaceuous earth. It’s like a fine, greyish powder from a certain rock. You sprinkle around you plant and/or on the leaves and it irritates the shell of bugs and they die. You do have to reapply after a rain as it gets washed away. We have a couple of bags of it in the shed (the ones wrapped in plastic bags). Feel free to use it on your cucumber, zucchini and other plants affected by the cucumber beetle. Wash your hands after putting it on and don’t breathe the dust (very fine). See http://en.wikipedia.org/wiki/Diatomaceous_earth for more info.
Hill Street Community Garden 