If they are not, jack them up, because they should be. Other gardeners are putting up mason bee homes, which are simple drilled wooden blocks, which are used by these solitary bee females for nesting sites. Stingless mason bees are excellent fruit pollinators, but not for garden veggies, because they go dormant after the spring. Bumblebee culture is also a booming business, but so far is so expensive that it is mostly used for greenhouse production of tomatoes, peppers, strawberries, etc. A visit by a bumblebee on your cuke blossom is worth about three visits by a honeybee, because the bumbler is so much more brawny and fuzzy.
Bumblebees are poor for fruit, because their populations are very small early in the season.
They are great pollinators for vegetables or very late blooming fruit, when their colonies are established. One third of our food supply must have bees. One bee going to a flower is not usually sufficient to make a quality fruit. Many flowers require 15 or 20 visits to make perfect fruit. Each time the bees come, they rub against the sticky pistil and smear on more pollen grains.