Do the tiny white insects look like cotton? If so, they may be mealybugs. If you can post a picture, perhaps we can tell for sure what insect it is affecting your plant. I didn't think I had any Syngonium indoors but I just went and looked around and I do have one growing in a terrarium. I haven't had mealybug issues in quite awhile thank goodness but in the past I had problems with mealies when I had plants all crammed together on my deck and there wasn't much air circulation. I've used Isopropyl Alcohol and q-tips to wipe the from plants that don't have heavy infestations but I always keep a spray bottle of Garden Safe brand Insecticidal Soap (available at Home Depot) in with my gardening supplies too ... it's a great product that takes care of mealybugs and a bunch of other insects.
A Syngonium in a terrarium, another in a pot sitting out in the yard and another outside, trailing from the pot and beginning to head up an oak tree.
