I have a 2-year-old gardenia plant on Cape Cod, MA. It's been replanted into a larger container a couple of times. Outdoors in summer; indoors in winter. I notice a very fine, small spotted (film?) on the leaves which seems to leave very small holes and is drying them. The plant is in a western window and receives periodic fertilizing, but has not bloomed. It isn't looking real healthy, although it has lots of new small leaves. I wipe them clean with my thumb and forefinger, but not sure it will remain clean.
Kill Aphids on Indoor Gardenia
Certified GKH Gardening Expert
I would recommend spraying the plant with neem oil. It is very effective against aphids and is organic and harmless to pets and people. You can find more information here: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm