Squash, pumpkins, melons, and cucumbers other than the parthenocarpic cultivars need insect pollinators. Most veggies including beans, corn, brassicas, okra, peas, tomatoes etc do not.

Corn is wind-pollinated, so it just needs a large enough population to provide good pollen density... hence the recommendation to plant corn in blocks. Okra & black-eyed peas will self-pollinate, but can be crossed if insects are present. Cantaloupe, like others of the gourd family, requires bees or other insects (or hand-pollination) to set fruit.