Aphids, maybe? I guess it will depend on what type of Hoyas you would be treating before advice can be given. Someone more knowledgeable about Hoyas will come along with some helpful advice.....

May those little critters be sent to bug heaven.

GH

Yep, could be milkweed aphids.
In the DG Hoya Forum is a thread regarding diseases and a picture of those critters is posted there. See if they look like yours.

Yes these are what I have seen on some of my hoyas. Can I use dish detergent as a spray?

Yes you can use soapy water spray or just blast them off with the water jet from a watering hose. Only problem is that they'll be coming back again soon with these methods but it somewhat controls their population.

If you decide to use dish soap, make sure that it is not antibacterial. If sprayed at the right times (at each life cycle) soap will help you kill them.

I get these buggers on the outside hoyas on new growth and on flowers that are about to open. Usually I hit them with Shultz Household Insect Spray (which does a fine job and doesn't seem to hurt even the new tender growth or buds). However, this year my 4 yr. old grandaughter is all "into" bugs, and worms, etc, so I picked up a container of those lady bugs they sell in nurserys this time of year. They even had a "lady bug house" complete with food and bedding for them. Ha. It is cardboard with cute little door and windows.
Anyway, I have a couple of large hoyas outside that were getting the usual springtime aphids on them, so we let a bunch of those ladybugs into their pots, and instead of flying away like I thoght they would do, they went right to work, and by afternoon....no more aphids on those plants.
Now...I really don't expect those ladybugs will stick around long enough to clear my garden of all it's evils, but it worked for a day on the plants we dumped them in, and was big fun for Katie to play with them and watch them in action. :-)
Marcy
PS: (none came back to their house today.) Ha.

Wow, Marcy, that is amazing. I've read that LBs kill aphids, but I've never tried it. I think I will get some when my GC finally gets this year's batch. They are pretty to look at too. Did you actually see the LB's devouring the aphids? Oh, what fun!!!!

GH

I grow Hoyas outdoors , so unfortunately we 'collect' aphids. They sure are a nuisance and even if you get rid of them , eventually others take their place .
I keep spray bottles handy , of Safer's Insecticidal Soap and Organocide horticultural oil. Before I spray , I look for ladybugs on the plants and relocate them to a safe place.
Then I hose off the ( happy ) dead aphid bodies.
Both products work , but I have to keep vigilant.

Florajilly