Cucumbers are the prima donnas of the veggie garden. Yellowing is a sign of lacking something; water, nutrients, sunlight, some or all of these.

Cucumbers are very hungry and very thirsty plants and need full sun, but don't get the leaves wet (mildew). Train them up a trellis and keep the ground moist. If they lack water at anytime, the cucs will taste bitter. I would remove the cover and let the bees at them and more light and rain. You can pollinate with a small paint brush or cotton swab or plant flowers nearby to draw the bees in (sunflowers work real well for this) Also certain companion plants will help keep the beetles at bay; marigolds, nasturtium, basil, onions.

Yellowing is also a sign of failed pollination. If these vines aren't really parthenocarpic, I'll have no choice. I'm wondering how to know for sure - other than waiting even longer for fruits to set - or not.

Some varieties of parthenocarpic still produce male and female flowers. Since you say the cucs are forming, something else is causing them to yellow.

Those don't sound like parthenocarpic cucumbers. If it were me, I'd just treat them as regular cukes and let them be pollinated.

No, the cukes aren't forming, that's the problem. The flowers fall off then the embryo turns yellow and shrivels. Like not pollinated.

The variety is alleged to be gynoecious as well as parthenocarpic, which is why the presence of male flowers bothers me. But given that there are male flowers, if the cukes won't form parthenocarpically, I'm thinking maybe I should expose them to the ravages of bacterial wilt and see if something will pollinate them. IF they will in fact pollinate.

But if they turn out to be parthenocarpic after all, I'm giving up prematurely.

otoh, if the beetles are going infiltrate the cover anyway, I might as well take it off.

My parthenocarpic butternuts (as they turned out to be) produce male flowers as well. The female flowers just don't seem to need them. But if your cukes are supposed to be gynoecious, then you have a problem.

I would just start ordinary cucumber plants since it's still early in the season. If you get anything off of the parthenocarpic plants, consider it a bonus. I never had much luck with cucumbers.

Bacterial wilt resistant cukes include County Fair (a great cuke) and Little Leaf--both bacterial wilt and downy mildew resistant.

I've tried some of those last year. Bacterial wilt killed them.

Also, the cukes that claim resistance all seem to be pickling varieties.