Hello, I have what seems like a honeydew all over the stems of my diplodemia. Can anyone help me get rid of the bug causing this? Any advice would be much appreciated! I attach a photo.

Hi Adeylle, Your lovely Mandevilla (also known as Dipladenia) appears to have Aphids. A strong spray of water will get rid of them or spraying with insecticidal soap.

Here are a couple of articles by members regarding Aphids and how to rid plants of them:
https://garden.org/learn/artic...
https://garden.org/learn/artic...

I found Aphids on leaves of a container plant on my patio this morning.

Thanks very much. Wonderful information!