Marigolds will deter Mexican Bean Beetles, but will probably not be completely effective. If you grow your beans and melons in rows try incorporating a row of marigolds in between each row of beans or melons. If growing in beds try getting them close to plants, but not so close the marigolds overtake everything. Neem oil does suffocate the eggs, and larvae of these bettles, but does not control the adults, which can be hand picked.