Hello Eric,
Welcome to this National Gardening forum.
" can the tubular petal flowers be insect pollinated? I have seen flowers that start out tubular, and then later petals are normal and the stigmas can be easily accessed, but in your fully tubular selections, Is there any insect crossing happening? "
Good question. I think the short answer is "no". The stigmas are inside a tube and they are inaccessible to an insect. So far my tubulars have been mostly propagated by floret seeds at the base of pollen florets, and occasionally by me breaking the tubes to expose the enclosed stigma. Tubular zinnia blooms are perfectly capable of seed production via floret seeds.
But, in my opinion, it is not even desirable for tubular zinnias to set seeds at the base of their tubes. If they did that, the plants would "go to seed" prematurely. That just would sap the energy of the plant. I do stay on the lookout for a tubular mutant that has a viable seed at the base of an intact tube, because that would be a significant development. But that will not imply insect pollination. It would be just be another mode of natural self pollination, like with the pollen florets.
We should be careful what we wish for. The inaccessible stigmas in tubes is probably a good thing, allowing the zinnias to display decorative blooms with out excessive seed production. Tubular petals can supply variety to zinnia blooms.
I have seen butterflies methodically inserting their feeding tubes down the tubes of tubular zinnias, as recently as day before yesterday, but that doesn't imply insect pollination. Apparently at least some tubular blooms have some nectar in the petal tube along with the enclosed stigma.
Butterflies and skippers actually do very little actual zinnia pollination. Their visits to a zinnia bloom to feed on available nectar are fairly gentle and they don't knock the pollen from florets around much.
Bumblebees and Honeybees and Hummingbirds do knock the pollen around and contribute significantly to zinnia pollination of normal petal stigmas. But even they do a lot more selfing than crossing. Most of the crossing in my zinnia garden is done by me.
We currently have a significant hummingbird population working our two hummingbird feeders that are near my zinnia garden and the hummingbirds also visit the zinnia blooms daily. Our Mimosa tree is still in bloom on some branches, and the hummingbirds visit those daily as well. So I
do not consider it a problem that tubular zinnia petals are not insect pollinated.
I think that tubular zinnia petals offer a variety of decorative looks to zinnia blooms, without endangering their ability to propagate.
ZM