Greetings fellow green thumbs!

I'm hoping you all can help me figure out what these bugs are... A type of aphid maybe?? I've had this issue for a few years, and they only seem to effect the same plants... My Sun Mandevilla Parisol. I have them around other plants like my oak leaf hydrangeas and dahlias, with no spreading. They stay only on the Mandeville, and seem to appear almost overnight!

As I hope you can see, they're yellow, and vary in size with the larger ones having black 'legs'. They will move if disturbed. I've tried neem oil and other insecticides, with little results.

Can you help?