More Bugs: Soft-shell scale, mealy bugs, spittle bugs, spider mites and cyclamen mites
A number of insects feed unnoticed on houseplants until perplexing changes alert you. Yellowing leaves are often seen as an indication that the plant is hungry and needs a dose of fertilizer. Yellowing leaves can also mean soft-shell scale insects are feeding on your rubber tree, crotons, philodendrons or related foliage plants. In sufficient numbers, these insects can cause leaves to turn yellow and appear deficient in nutrients.
Look for scale insects on stems, veins in leaves and leaf tissues between the veins.