A squash bore is a larva that bores a hole into the stems of squash and eats the core of the stem. This causes parts of the plant to wilt and die. Spray early in the season with a good vegetable pesticide.
Russell Feed & Supply offers a couple different chemical control products that can be used as a preventive or if you have a problem with squash bores in your garden. First, you can spray with Biological Spray Bt (Bacillus thuringiensis) or pyrenthrins along the stems of the plant. Another option is to try Carbaryl (Sevin) that can be applied as a spray or dust.