These are males and females which are located at different places on the plant. This condition is called monoecious. This is called pollination. Fertilization then takes place and seeds and fruit are produced. Cucumbers and watermelons generally have both male and female fruit-producing flowers.
Insect pollination is necessary for commercial production of most vine crops.
The honey bee traditionally has been the preferred pollinating agent. Although benefitting from honey bee pollination, most vine crops are poor sources of pollen and nectar. This means that honey bees cannot be expected to make any significant population gains while located on these plants. Indeed, the opposite is often the case. The best review of pollination requirements of specific crops continues to be Agricultural Handbook 496, Insect Pollination of Cultivated Crop Plants , by S.E. McGregor, published by the Agricultural Research Service, USDA, July, 1976.