Hi Cukes!
Your cucumber might be still young so the pollination process is not yet ready for the female flowers.
You'll notice that cucumber has two separate flowers; the male and female. In their early growth, the first to come out are the male flowers, these are the flowers that will pollinate the female flowers. The second stage to come out are the female flowers.
So, once these two flowers comes together, then there will be pollination process that will takes place, of course with the presence of pollinating insects (e.g. bees, butterflies, etc.).
Therefore, extra care must be observed when you use insecticides to control some insect pests - you might kill these insects that helps you pollinate your flowers.
The best remedy is use organic farming to avoid destroying those friendly insects.
Happy gardening!
Cris
www.crisramasasa.com