My neighbor had a huge problem with potato bugs. If the patch is small, pick them off by hand and drop them into soapy water to kill them. Or else buy floating row covers, which let in light and water but keep out insects. The short term solution is to do what I just said. The long-term solution is to design a garden that has a wide host of plants that will attract a wide host of bugs.
Diversity is the key.
No magic, and chemicals from a bottle aren't the answer. They kill off bad and GOOD bugs. So your garden is vulnerable for the next wave of predators. Yes, that's a common organic approach. You can buy lady-bug beetles through the mail, for instance.