Common name: Aphids
Scientific name: Hundreds of species of aphids
Hosts: There is a wide range of hosts, depending on the species of aphid. Some species feed on only one host, some alternate between two host species and others feed on a number of hosts.
Aphids are soft-bodied, pear-shaped insects. They are very small, with most species under 1/8 inch in length. Aphids can be almost any color. Some are covered with a threadlike white material, which makes them appear woolly, while others may be covered in a fine dust. There are both winged and wingless individuals of most species.
Aphids can be identified by a beak-like mouthpart (rostrum) that sits far back on the underside of the head. Their antennae are rather long and placed in the front of the head, between the eyes. Aphids have a pair of projections, called cornicles, on each side of their posterior. These structures are reduced in size on some species. The cornicles are used to emit alarm pheromones to warn other aphids of nearby predators.
As individuals, aphids do little harm to a host plant, but large infestations can produce noticeable damage. Their behavior is determined largely by food preference and feeding site. Most are seen on the leaves, stems, and foliage of plants, especially on the new growth, but there are species that feed underground on roots and bulbs. Some produce galls or other deformities.
Damage
An aphid feeds on its host plant by inserting its beak-like mouthparts into plant tissue and sucking out sap. Aphids are often found in groups clustered on the new buds, stems, and young leaves or shoots and the feeding of these groups can cause decline in the health of the host.
Infested plants often show distorted growth that may be curled, puckered, or otherwise stunted. Leaves may show pale or yellow spots or entire leaves can turn yellow or brown. Flower buds and flowers may also become shriveled or reduced in size. Seedlings and tender ornamentals can be noticeably deformed by an infestation of aphids.
Aphids produce ‘honeydew’, a sticky substance that can provide a favorable environment for the growth of sooty mold, which blocks light from the plant tissue. The honeydew also attracts ants. These ants, in turn, take care of the aphids, even killing aphid predators.
Viruses can be spread by aphids. The possibility of virus transmission during feeding can be more serious than the feeding damage done by the aphids.
Life Cycle
Many species of aphid have a similar life cycle, presented here in a simplified overview. They overwinter in the egg stage, with the eggs often being protected by bark or ground litter. The eggs hatch in the spring, producing a generation of wingless, all-female aphids. These female aphids are parthenogenetic, meaning they can reproduce without being fertilized by a male. The next generation produced is also all-female and they are born with embryos in their bodies (essentially born pregnant and ready to reproduce). This allows for aphid populations to grow very quickly. The number of generations per year will vary by species, but, generally, only female aphids that can give birth to living young without mating are present during the summer. In late summer, reductions in day length and temperatures will trigger the development of male aphids, as well as females that can mate and lay eggs.
Management
Cultural Management
Aphids are attracted to the color yellow. Commercially available yellow sticky traps can be placed near susceptible plants to serve as traps. Aphids deposit eggs in leaf litter and twigs, so good garden sanitation in the fall and a thorough clean-up of flowerbeds in spring will help to eliminate sites where eggs may overwinter.
Aphids generally congregate in groups near the tips of stems. Cutting off the tip of the stem can remove an entire colony at once. Light infestations can be controlled by washing the plants with a forceful jet of water, paying particular attention to the undersides of leaves. Wash off new populations as soon as they are seen to minimize damage to the host plant.
Biological Management
Fortunately, aphids have many natural enemies that are very effective in controlling infestations. Chief among these are lady beetles, with both adults and larvae feeding on aphids. Other major predators include lacewings, small parasitic wasps, syrphid flies (hoverflies), and soldier bugs. Avoid the use of any chemical sprays to encourage and protect these natural enemies.
Another good practice is to encourage winter songbirds to visit your garden because many birds will search tree bark for overwintering aphid eggs. Good varieties are chickadees, nuthatches, purple finches, and warblers.
Chemical Management
Chemical management of aphids is often not necessary. Natural enemies and non-chemical measures offer good results on their own. If the situation needs chemical management, contact the Plant Clinic (630-719-2424 or plantclinic@mortonarb.org) for current recommendations.
For more information, contact The Morton Arboretum Plant Clinic (630-719-2424 or plantclinic@mortonarb.org).