I have straight eights planted in a raised with tomatoes planted late April. So far only one female flower it went unfertilized although I have lots pollinators of different kinds all over the perennials planted near by. The vine looks great and I tossed in some slow release balanced fertilizer. Any ideas or is this just a bad cucumber year in Northern Virginia?
Female flowers are the fewest on the main stem and their number is greatest on 3rd level of ramifications.
Also, when the plant is young it will produce a female flower for every 10 male flowers, and the number of female flowers grows with the plant's age.
Drought results in more male flowers. Low temperatures results in more female flowers.
Update: As suggested in the comments, I'm adding the source of the above info. It's a book called "Cultivation of vegetables", 3rd edition (2012), coordinated by D. Indrea. The chapter regarding cucumbers is written by D. Mănuțiu and he provides a table for causes of the variation of flower gender. This table has a citation that states the info came from an old book "Legumicultura" by M. Bălașa, published in 1973.
Unfortunately, I don't have an English version of the book.