Generally speaking natures work horse, the bumble bee, is the primary vessel through which cucumbers are pollinated. Bees however are commonly hampered in the task of pollinating our gardens by over zealous and poorly informed gardeners using broad spectrum pesticides that kill off pests as well as beneficial insects, bees.
Poorly planned gardens will also fail to attract very many bees and other pollinators. A well balanced garden should include a diversity of symbiotic plants, vegetables, herbs, fruits and berries, and even some ornamental flowers to draw in as many bees as possible. If you believe your garden is not attracting as many bees as is desirable hand pollination is an option. See: Hand Pollination.
When a full dose of pollen is received by the stigma of the female flower, the finished cucumber should be a quality fruit, barring other negative variables. It should mature quickly into a crisp and crunchy cucumber fit for a salad or brine.
Quality cucumbers need to grow rapidly for optimal quality. Temperature fluctuation, nutrient issues - fertilizer, fluctuations in moisture - water, excessive malevolent insect activity or plant disease are the other negative variables. Slow growing cucumbers are usually bitter and lack the crunchy crispness we have come to expect from our cukes.
Related Declining Bee Populations Cucumber Bacterial Wilt
Why Cucumbers Turn White Cucumber Insect Problems Cucumber Mosaic Virus