How to recognise it
The initial signs may be the appearance of tiny while skin shells on and round the plant, which are shed by the aphid nymphs during a process called ecolysis. As the infestation increases the aphids become clearly visible on the plant.
You may also notice sooty mould growing on the plant, this is attracted by the honeydew aphids excrete after feeding. The toxic saliva the aphids secrete can also cause leaf distortion and/or discolouration.
The aphids themselves are often found on the stems of plants and also on the underside of leaves, the areas which make them closer to the plant’s phloem, from which they feed. They are generally 1 to 5mm long with soft bodies, relatively long legs and antennae and usually a conspicuous pair of tube like structures at the rear end of the abdomen. The body colour varies between species. Colonies include both winged and unwinged adults.
Aphids have an incomplete lifecycle, being classified as endopterygeta insects. Eggs, laid at the end of the previous season on plants to overwinter, hatch in spring producing wingless ‘nymphs’, all of which are female. The nymphs are born pregnant and continue to produce live young (again all female and all pregnant) while all living on the same plant, hence the rapidness with which an aphid infection can spread. In summer temperatures the nymphs mature in about a week, therefore populations can increase very rapidly.
With some species, if the food supplies start to run out, a proportion of the aphids will grow wings and fly to new plants where they will give birth to further live young, so continuing the cycle.
In some species, when the temperature and day length starts to decrease in autumn this triggers the production of male aphids. They then mate with females which enables the females to produce eggs (instead of live young) which can survive the winter. The live aphids then all die out over winter. In other species only asexual reproduction is found.
Why it’s a problem
As well as sapping the plant’s own food supplies (aphids suck food out of the phloem transport system within the plant) and excreting honeydew which can attract sooty mould, they can also act as ‘vectors‘ (carriers) for plant viral and fungal diseases – they are the most common form of transfer for some diseases. This is the case for both nymph and adult aphids.
Where you are likely to find it
Aphids can potentially be found on any plants (eg broad beans, roses, clematis, tulips, penstemon, tropeolum and lupins), but there are some types which have particular hosts:
Found on fruits – rosy apple aphid, rosy leaf-curling aphid, apple-grass aphid, green apple aphid, woolly aphid, pear-bedstraw aphid, peach-potato aphid, leaf-curling plum aphid, mealy plum aphid, damson-hop aphid, cherry blackfly, currant aphids, gooseberry aphid, raspberry aphid and strawberry aphid.
Found on vegetables – black bean aphid, cabbage aphid, currant-lettuce aphid, lettuce root aphid, willow-carrot aphid, pea aphid, melon and cotton aphid, potato aphid and glasshouse and potato aphid.
Found on ornamentals – rose aphids, chrysanthemum aphids, mottled arum aphid, tulip bulb aphid, honeysuckle aphid, lupin aphid, viburnum aphid, elder aphid, privet aphid, violet aphid, water-lily aphid, lime leaf aphid, birch aphids, sycamore aphid, beech aphid, large willow aphid, green spruce aphid, fern aphid, root aphids, cypress aphid and juniper aphids.
How to deter it
Once grown, removing the tips from plants such as broad beans can discourage aphids by removing the succulent growth they are normally attracted by.
Companion planting(eg of Allium spp.) can be an effective deterrent either by repelling the aphids or by attracting predatory insects.
How to get rid of it
Nymphs and eggs can be manually removed by hand or by a strong spray from a hosepipe.
Encourage natural predators such as lacewings, hoverflies, ladybirds and blue tits.
Biological controls for aphids include the predatory midge Aphidoletes apidomyza, the larvae of which eats aphids. Alternatively Aphidius spp., a parasitic wasp, lay their eggs in aphids, the larvae developing within the aphid and then eating its way out.
Chemical controls include pyrethrum, fatty acids (on nymphs and adults) plant oils, synthetic pyrethroid compounds (such as bifenthrin), acetamiprid, imidacloprid and thiacloprid.
Is it good for anything?!
Other useful information
Ants ‘milk’ aphids for their honeydew, however they don’t kill the aphids in the process and can in fact protect the aphid colonies from predators.
More than 500 aphid species exist in Britain alone. Most are individual to just one or a few plant species, but some have a wider ranging impact.
We have information on the following species of aphid: