Answer: Mealybugs look like fluffy little white bits of cottonwool and tend to sit at the juncture of branches, here are some photos of mealybugs just to make sure this is the problem.
The first thing to do is isolate the plant because this pest is prone to spreading. They reproduce by eggs, so it is possible they were on the plant or they may have hitchiked in on another new plant or just hopped on over because they are a fairly common pest in greenhouses.
You can try dabbing at them with a swab dipped in rubbing alcohol but this is pretty time consuming. Washing the plant with a good spray of tepid water from the spray attachment at a sink can do a good job of knocking them down. Try this once a week and it will help keep the foliage clean as well as help control mealybugs, aphids and spidermites -- another common ivy pest during the dry winter heating season.
You can also use insecticidal soap being sure to read and follow the label instructions per dilution rate and the timing of follow up treatments. Be sure to contact all surfaces of the plant with the spray. (Insecticidal soap is effective against not only mealybugs but also scale which is another relatively difficult pest to control on ivy houseplants.)
Good luck with your ivy!
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