Aphids
Beginner
Scientific Name
Myzus persicae (green peach aphid), Macrosiphum euphorbiae (potato aphid), other aphids
Identification
- Small, pear-shaped insects, with cornicles or “tail-pipes” near the tip of their abdomen
- Typically found in colonies located on the underside of the leaf, or along the stem or petioles
- Aphids pierce the leaves and suck the sap from many vegetable crops, causing stunting, leaf yellowing, or leaf distortion if severe
- Aphids secrete honeydew, leading to sticky residue and sooty mould on the fruit and foliage
- Aphids act as a primary vector of several economically significant virus diseases, spreading the virus as they feed
Often Confused With
Tarnished plant bug nymphs
Leafhoppers
Period of Activity
Aphids are present throughout most of the growing season. Populations build quickly during hot, dry weather. Aphid populations are often kept below threshold levels where predators (lady beetles, lacewings, minute pirate bugs, etc.) and parasites are present in abundance.
Scouting Notes
Carefully inspect 10 groups of 10 plants across the field. Watch for the presence of aphids on the developing fruit. Take note of any aphid populations that continue to build over a several week period. Inspect the underside of leaves from the top, middle and bottom of plants. Note the presence of aphid honeydew on the foliage and fruit. Look for beneficial insects (aphid predators or parasites) as well. Look closely to distinguish live aphids from dead aphids and moulted aphid skins.
Threshold
None established. If high populations are causing significant visual plant damage or the fruit are becoming contaminated with honeydew or sooty mold, treatment may be warranted.
Advanced
Scientific Name:
Myzus persicae (green peach aphid), Macrosiphum euphorbiae (potato aphid), other aphids
Identification
Green peach aphids are uniformly creamy white, green or pink. They are opaque in appearance rather than shiny. Potato aphids may be pale green to yellowish or pinkish. Aphid colour is not a reliable way of distinguishing species. Either species may be winged or wingless.
Aphids have long, piercing mouth parts which allow them to suck juices from the plant. Heavy infestations can cause the foliage to become stunted, distorted, or yellow. The plant may also be covered with whitish, moulted skins and the bodies of dead aphids. Aphids exude a sticky honeydew that supports the growth of a black, sooty mould on the surface of leaves or fruit. Under dry conditions, aphids may reduce growth enough to affect yield.
Often Confused With
Tarnished plant bug nymphs
Leafhoppers
Biology
Aphids can take two forms, a winged form, capable of migrating across considerable distances, and a wingless form, that remains in place on one plant. As aphids become crowded, or the host plant begins to deteriorate, winged forms are produced. When these winged forms find suitable hosts, they produce wingless offspring. These wingless offspring are capable of reproducing without mating resulting in 'colonies' of wingless aphids that remain in place on the host until conditions deteriorate and more winged forms develop.
The green peach aphid overwinters outdoors as a small black egg on the twigs of peach and other Prunus species. Several generations develop on peach in the spring before the winged forms are produced which migrate to a large number of summer hosts. The wingless forms then develop on the summer host. Significant numbers reproduce indoors on numerous plant species and will escape outdoors when the weather becomes favourable. As well, bedding plants and transplants can become infested in the greenhouse. Potato aphids overwinter as eggs on rose species.
Period of Activity
In Ontario, aphids can be found beginning in late spring. Aphids are present throughout most of the growing season. Populations build quickly during hot, dry weather. Aphid populations are often kept below threshold levels where predators (lady beetles, lacewings, minute pirate bugs, etc.) are present in abundance. While aphids can be found on plants early in the season, damaging levels usually occur after mid-summer.
Scouting Notes
Aphids may be patchy within a field. Populations are often higher initially along field margins and hedgerows. Inspect the underside of leaves from the top, middle and bottom of plants. Note the presence of aphid honeydew on the foliage and fruit. Look for beneficial insects (aphid predators or parasites) as well. Look closely to distinguish live aphids from dead aphids and moulted aphid skins.
Thresholds
None established. If high populations are causing significant visual plant damage or the fruit are becoming contaminated with honeydew and sooty mold, treatment may be warranted.
Management Notes
- There are numerous species of predatory and parasitic insects which serve to regulate aphid populations. Important predators include the lady beetles, minute pirate bugs, lacewing larvae, syrphids, predatory midges, ground beetles and spiders. Aphids are also commonly attacked by small parasitic wasps such as Diaretiella rapae. Aphids that contain a developing parasite swell and turn a papery grey or brown.
- Aphid numbers often increase dramatically after the application of insecticides which are detrimental to beneficial insects.
- Later in the season, large numbers of aphids frequently become infected with fungal diseases. Outbreaks of disease are favoured by dense plant canopies, large aphid populations, and moist conditions. Periods of heavy rain can directly dislodge aphids from plants and promote the development of these diseases.
- In addition to direct feeding damage, aphids also vector viruses such as cucumber mosaic virus. Aphids transmit the virus in a non-persistent manner, meaning that an aphid can acquire the virus from an infected plant and transmit it to a healthy plant after feeding for a very short period of time. Insecticides are not an effective means of controlling cucumber mosaic virus, as infection occurs very rapidly and plants will become infected before aphids are killed. Aphids colonizing tomatoes, as well as winged migrant aphids can vector the virus.
- In years of high soybean aphid populations, the volume of aphids moving through the landscape (probing other crops as they search for soybeans) may spread vegetable crop viruses.
