Aphids are small, soft-bodied, sap-sucking insects. A few dozen of them are among the most damaging pests of crops worldwide: they multiply faster than almost any other insect, feed on nearly every crop, and are the most common carriers of plant viruses. This page explains the biology the species share, how they transmit viruses, and the principles of managing them. Each species has its own page with identification, life cycle and thresholds.
What aphids are
Aphids belong to the true bugs (order Hemiptera) and to the family Aphididae. Several thousand species are known, of which around a hundred are important on crops. Most are 1-4 mm long, pear-shaped and green, yellow, grey, pink or black, sometimes with a waxy coating.
Two features help recognise them: a pair of short tubes near the rear of the abdomen (cornicles or siphunculi) and a small tail (cauda). Aphids feed with needle-like mouthparts that reach the phloem, the plant's sugar-transport tissue. Because phloem sap is rich in sugar but poor in protein, aphids excrete the surplus sugar as sticky honeydew.
Aphid life cycle: why numbers explode
For most of the year, crop aphid colonies consist only of females that give birth to live young without mating. A newborn aphid already carries the developing embryos of the next generation inside it, so generations overlap ('telescoping generations'). In warm weather a nymph becomes an adult in about a week, and a colony can double in a few days.
Most aphids in a colony are wingless. Winged forms develop when colonies become crowded, when the plant declines, or when day length changes. Winged aphids carry the infestation, and any viruses, to new fields, often over long distances on the wind.
In temperate regions many species have a sexual generation in autumn. Females lay eggs that survive the winter, often on a different 'primary' host: the green peach aphid on peach and other Prunus trees, the bird cherry-oat aphid on bird cherry, and the soybean aphid on buckthorn. In warm regions, and in many invaded areas, aphids skip the sexual stage and reproduce asexually all year.
How aphids damage crops
Sap feeding: dense colonies weaken plants, stunt shoots and reduce flowering and pod or grain set.
Toxic saliva: some species inject saliva that streaks, rolls or yellows leaves even at modest numbers. The Russian wheat aphid is an example.
Honeydew and sooty mould: sticky honeydew covers leaves, fruit and cotton lint, and black sooty mould grows on it, reducing photosynthesis and quality.
Virus transmission: often the most costly effect, because a few winged aphids can spread a virus through a crop long before colonies are noticeable.
The aphids covered in this encyclopedia
Green peach aphidMyzus persicaeInsect · A small, soft-bodied aphid found on hundreds of crops worldwide. Colonies curl leaves and leave sticky…
Cotton aphid (melon aphid)Aphis gossypiiInsect · A small aphid, from pale yellow to almost black, that forms dense colonies under the leaves of cotton,…
Cowpea aphid (black legume aphid)Aphis craccivoraInsect · The cowpea aphid is a small, shiny black aphid that forms dense colonies on the growing tips, flowers and…
Mustard aphid (turnip aphid)Lipaphis erysimiInsect · The mustard aphid is a small grey-green aphid with a waxy coating that forms dense colonies on the flowering…
Soybean aphidAphis glycinesInsect · The soybean aphid is a small yellow aphid from East Asia that colonises the undersides of soybean leaves and…
Russian wheat aphidDiuraphis noxiaInsect · The Russian wheat aphid is a small, lime-green, spindle-shaped aphid that feeds inside rolled leaves of wheat…
Bird cherry-oat aphidRhopalosiphum padiInsect · A dark olive-green aphid of wheat, barley, oats, maize and grasses, recognised by a rusty-red patch around…
Sugarcane aphid (on sorghum and sugarcane)Melanaphis sacchariInsect · A small pale yellow to grey aphid that forms dense colonies on the undersides of sorghum and sugarcane…
How aphids transmit plant viruses
Aphids are the most important vectors of plant viruses. Viruses are carried in different ways, and the way a virus is carried decides which control methods work.
Non-persistent (stylet-borne): the virus sticks to the mouthparts and is picked up and passed on within seconds of probing, then lost within minutes to hours. Aphids that never colonise the crop can still spread it while testing plants. Examples are potyviruses such as potato virus Y, bean common mosaic and papaya ringspot. Insecticides cannot act fast enough to stop this, so control relies on clean seed, resistant varieties, barriers, timing and roguing.
Semi-persistent (foregut-borne): the virus is retained in the foregut for hours to a few days, and longer feeding is needed to acquire it.
Persistent, circulative: the virus passes through the aphid's gut into its body and salivary glands. Acquisition needs minutes to hours of feeding, a latent period follows, and the aphid then stays infective for life. Examples are potato leafroll virus, the barley and cereal yellow dwarf viruses, the assistor virus of groundnut rosette and banana bunchy top virus. Because colonising aphids must feed for some time, controlling them does reduce spread.
Managing aphids: IPM principles
Aphid management works best when it combines several methods and when chemical control is used only where it pays.
Monitor: count aphids on a set number of plants, using local thresholds where they exist, and watch flights with yellow water traps or regional suction-trap networks.
Protect natural enemies: ladybirds, hoverfly and lacewing larvae, parasitic wasps that leave mummified aphids, and fungal diseases often stop outbreaks on their own. Broad-spectrum sprays that kill them commonly lead to aphid resurgence.
Grow resistant or tolerant varieties where available, and use virus-free seed and planting material.
Use cultural methods: remove volunteers and weed hosts, avoid excess nitrogen, adjust sowing dates to avoid peak flights, and use netting, reflective mulches or barrier crops where viruses are the main risk.
Choose insecticides by mode-of-action group, rotate groups between generations, and check local resistance status. The green peach aphid and the cotton aphid have developed resistance to many groups.
Virus diseases they spread
Potato virus Y (PVY)Potato virus YVirus disease · Potato virus Y is the most important virus of potato worldwide and also attacks pepper, tomato and tobacco.…
Potato leafroll virus (PLRV)Potato leafroll virusVirus disease · Potato leafroll virus makes the lower leaves of potato plants roll upward, become stiff and leathery, and…
Bean common mosaic and bean common mosaic necrosisBean common mosaic virus and Bean common mosaic necrosis virusVirus disease · Bean common mosaic and its close relative bean common mosaic necrosis are virus diseases that mottle bean…
Papaya ringspot disease (PRSV)Papaya ringspot virusVirus disease · Papaya ringspot is the most destructive disease of papaya worldwide. Aphids spread the virus in seconds as…
Groundnut rosette diseaseGroundnut rosette virus complexVirus disease · Groundnut rosette is the most destructive virus disease of groundnut in sub-Saharan Africa. Infected plants…
Banana bunchy top disease (BBTV)Banana bunchy top virusVirus disease · Banana bunchy top is the most destructive virus disease of banana and plantain. Infected plants grow narrow,…
Sweet potato virus disease (SPVD)Sweet potato feathery mottle virus with sweet potato chlorotic stunt virusVirus disease · Sweet potato virus disease is the most damaging disease of sweet potato. It develops when a plant is infected…
Chemical control: IRAC mode-of-action groups
Chemical options for aphids are named here only by IRAC mode-of-action group. Products, and what is registered, differ by country and change over time, so follow the label and your local plant-protection authority. Groups commonly used against aphids include:
The evolution of insecticide resistance in the peach potato aphid, Myzus persicae — Insect Biochemistry and Molecular Biology (Elsevier). https://doi.org/10.1016/j.ibmb.2014.05.003
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