Identification
Small (1–3 mm) soft-bodied insects, green, black or pink, feeding in clusters on young shoots and the underside of leaves. They excrete sticky honeydew. The diagnostic feature that distinguishes aphids from other small sucking insects is the pair of siphunculi (tubular projections) at the rear of the abdomen together with a tail-like cauda; a single colony usually holds wingless forms (parthenogenetic females) alongside winged migrants that fly onto new plants in summer. In summer aphids reproduce parthenogenetically and viviparously over many generations, so the population builds up explosively; in autumn many species produce a sexual generation that lays overwintering eggs on the host, and host-alternating species move between a winter host (often a tree or shrub) and a summer host (a herbaceous plant). Feeding symptoms include curling, crinkling and distortion of young leaves, stunted growth, yellowing, and the shedding of buds and fruitlets. Abundant honeydew coats the leaves, and the sooty mould fungus that develops on it forms a black film which limits photosynthesis; the honeydew is fed on by ants, which in return defend the colony against predators. Aphids are also important vectors of plant viruses (mosaics among them), transmitting them from plant to plant even during a brief probing puncture.
Treatment
Washing off with a strong jet of water, potassium soap, introducing ladybirds and lacewings, and insecticides as a last resort. The water jet and potassium soap (or an oil-based contact product) act only at the point of direct contact — they destroy the outer covering and desiccate the insects, but have no follow-on (residual) action, so they require thorough wetting of the leaf undersides and repeat treatments every 5–7 days. Biological control is most effective early: besides ladybirds and lacewings, aphids are controlled by hoverfly larvae, the aphid midge (Aphidoletes) and parasitic aphid wasps (Aphidius) — it is worth supporting them with nectar-bearing plants and avoiding broad-spectrum insecticides that wipe them out. As prevention: moderate nitrogen fertilisation (excess nitrogen gives lush, soft growth preferred by aphids), monitoring with yellow sticky traps, and controlling ants, which 'farm' aphids and protect them from natural enemies. Chemically and only as a last resort: a contact pyrethroid quickly knocks the population down but destroys beneficial insects and encourages resistance, whereas a systemic product selective against sucking insects acts for longer — treatments are done outside pollinator flight times (in the evening) and modes of action are rotated (IRAC) to limit resistance build-up. Neonicotinoids are heavily restricted or banned in field crops in the EU, so they are not a routine solution.
How to tell it apart from look-alikes
| Feature | Aphids | Glasshouse whitefly |
|---|---|---|
| Appearance of the adult insect | Soft, pear-shaped insects 1–3 mm, green, black, pink or yellow; usually wingless colonies with occasional winged individuals | Small (1–2 mm) white insects with wings coated in a waxy powder |
| Reaction when the plant is disturbed | Remain motionless in the colony | Take off en masse in a white cloud |
| Body-structure feature | A pair of siphunculi and a cauda at the rear of the abdomen | No siphunculi; motionless larvae that are flat, transparent and stuck to the leaf underside (resembling small scale insects) |
| Honeydew and sooty mould | Abundant | Abundant — a shared symptom that does not by itself distinguish the culprit |
Control — organic and chemical methods
Organic and biological methods
| Method | How it works | When to use |
|---|---|---|
| Washing with a jet of water | A strong jet of water knocks the colonies off shoots and leaves; a supporting method that must be repeated, because some of the insects return. | As needed, at the start of an infestation |
| Potassium soap (soft soap) | A contact product — it dissolves the waxy covering and desiccates the soft body; it acts only on wetted insects, so thorough wetting of the leaf undersides and repeat treatments are essential. | — |
| Oil-based contact product | Oil (rapeseed, paraffin) blocks the spiracles and suffocates the insects and their eggs; a contact product with no systemic action, not to be applied in full sun or heat. | — |
| Natural enemies (biological control) | Ladybirds, lacewings, hoverfly larvae, the aphid midge (Aphidoletes) and aphid wasps (Aphidius) reduce the population; support them with nectar-bearing plants and do not wipe them out with insecticides. | From the early stage of infestation |
| Agronomic prevention | Moderate nitrogen fertilisation, monitoring with yellow sticky traps and controlling the ants that farm aphids; this slows the build-up of the colony but does not eliminate it on its own. | — |
Chemical methods
| Method | How it works | When to use |
|---|---|---|
| Contact or systemic insecticide | A contact pyrethroid quickly knocks the population down (at the cost of beneficial insects), while a systemic product selective against sucking insects acts for longer; rotate modes of action (IRAC) and protect pollinators. | A last resort, in a mass outbreak |
We give active-ingredient groups and modes of action, not brand names — specific products and their approval vary by country and are sometimes withdrawn. Always check and follow the current label.
Sources
- Atlas of plant pests
