NIPs can be prone to scale insects, mealybugs, whitefly, but most especially spider mites. Those are the primary pests of these particular plants.

Scale insects of any species can readily be seen by the naked eye when they are adults or nearly so. Look for small bumps along the stem or needles. Scale insects often excrete a clear, sticky substance that can cover the stems and any surface below the plant.

Pictures of common scale species can be found readily on Goggle Images.