To properly diagnose an insect problem on ornamental plants, it is generally best to visually see the organ-ism causing the problem. However, sometimes it is also possible to rely on insect leftovers as a means to determine the cause of the problem.
Insects can leave subtle reminders or remains, which indicate that they have been there.
Aphids, for example, leave white cast skins as evidence of molting. These cast skins may be mistaken for whiteflies or dead aphids. Many insects with piercing sucking mouthparts produce a clear, sticky liquid called honeydew as evidence of their presence. Plant sap contains an assortment of other materials in larger quantities than amino acids. Third, it is an excellent growing medium for black sooty mold fungi, which may reduce the plant s ability to manufacture food.