If left unchecked, aphids can stunt plant growth, deform and discolor leaves and fruit, or cause galls to form on leaves, stems, and roots. Some species also produce large amounts of white waxy filaments that cover their bodies and litter infested plant parts. This energy-rich anal secretion falls on leaves and other objects below the infestation. As a result, sunlight is unable to reach the leaf surface, which restricts photosynthesis which produces the plant sugars. Honeydew-covered surfaces, including car exteriors, decks, and sidewalks, become sticky and blackened with sooty mold.
Honeydew also attracts ants, flies, and other insects.
Some aphid species depend heavily on ants for survival and dispersal. Ants also carry aphids to uninfested parts of plants. The cotton aphid is known to transmit more than 50 plant viruses, and the green peach aphid more than 100. Aphids can occur anywhere on the plants, but they are often found on the underside of the leaves or on the new growth. Yellow sticky cards, available from garden stores and nurseries, are effective tools for monitoring winged aphid populations, particularly in greenhouses.