If bees fail to pollenize these flowers, the fruit will start to develop but shrivel and fall off. If bees pollenize the flowers only sparingly, the fruit may develop but be misshapen or poorly filled. Many questions also arise regarding cross-pollination of plants in the garden. For all practical purposes, this does NOT happen. Each of these crops has different chromosome numbers which means they will not cross with one another even if you tried.
Cucumbers cross only with other cucumbers, etc.
In addition, you would not see the result of any cross until you planted the seed from a fruit produced this year and grew out the resultant fruit in the next generation next year. Remember self-pollenized crops do not cross with anything else. The vine crops are insect pollenized so that crossing might happen ONLY for crosses within the crop and ONLY if you save your seed for next year's crop. In plants that are self pollenized, this is not a problem with bees. Many plants set more flowers than the plant can develop fruit.