Do they wipe off or do they seem to be a permanent part of the plant? I can't say I've ever seen anything quite like it. Can you tell us where you grow these? Indoors or out? Sun exposure - do they get full sun, dappled, morning only, etc.? The color of the bumps makes me think aphids, but they usually attack young stems and they're big enough to be identifiable. However, I know there are many species of aphids that differ from region to region. Aphids do love Hoyas, which is why I don't put very many at all outside...

If we can't figure it out here, I'd take a leaf to your local extension office (I assume all states have them). I have an old, old Hoya aldrichii that started getting yellow polka dots on the topside of the leaves last winter and it spread through the whole large plant. I took a leaf to our cactus club meeting yesterday as we have a horticulturist in the membership and even he was baffled. However, one of our members is a master gardener and she will take it to the extension office today and they will put it under a microscope and she said they have experts who will be able to definitively tell me what it is.

Denise in Omaha

These look like edema to me, which is sort of a humidity-related issue - the plant unable to transpire water as quickly as it takes it up.

If they don't move around or wipe off fairly easily it's probably edema. You could always take a leaf to a large nursery/garden center that should have a botanist.

Thanks for the answers. I keep it inside, in a bright east facing window but it doesn't get direct sunight. The bumps are part of the plant, I cant wipe them off so they are not aphids. Im from Hungary, Europe, we had temperatures around 100F in the last weeks so I hope its just some reaction to the heat. I cut the leaves off, just to be sure.

Hey Jake - my parents are from Hungary. I saw my first Hoya at my grandparent's house in Herend. It was a Carnosa that was huge with vines about 4 feet long and covered with flowers. It must have been a Carnosa Snowball because the flowers were large and almost completely round.

I have such wonderful memories of that plant (and visit with family) and that was 40 years ago.