As a result, sunlight is unable to reach the leaf surface, restricting photosynthesis that produces the plant sugars. Honeydew also attracts ants, flies and other insects. Some species are heavily dependent on ants for survival and dispersal. The honeydew-loving ants 'tend' the aphids and prey upon natural enemies of aphids and otherwise unhealthy aphids. Ants also carry aphids to uninfested parts of plants.
Aphids are important vectors of plant diseases, particularly viruses.
However, any aphid may be considered a potential pest when conditions are favorable for reproduction. The reproduction rate of aphids is dependent upon food quality, host plant species and temperature. Food quality can be controlled to some extent by applying fertilizer and other chemicals. A listing of biological control agents, non-chemical methods and insecticides for suppressing aphid infestations on ornamental plants is presented in Table 2 . Chemical control of certain aphid species has become extremely difficult due to resistance to insecticides, particularly organo-phosphate, carbamate and pyrethroid insecticides.