Often simply referred to as green fly or black fly, these soft-bodied, 1 to 7 mm (up to about 1/4 in) long sap sucking insects actually include a variety of species. Typically pear-shaped and featuring long legs, some of these species are wingless, while others have wings. Colours vary from pink, black and yellow to white, red, green or mottled, and some of them - such as, for instance, the Woolly Beech Aphid and the Woolly Aphid - are often confused with scale insects, whitefly and mealy bugs, because they tend to cover themselves in the same fluffy, waxy white secretions.
Some Aphid species predominantly feed on plants' stems, foliage and flowers, while others attack the roots. They will appear any time - regardless of season - and multiply rapidly, causing a whole lot of damage before moving on to the next plant. In addition to the damage their feeding causes, many species transmit viruses from plant to plant, and all of them will leave secrete honeydew, a sticky substance likely to attract black sooty moulds.
Symptoms of Infestation
Typically attacking new plant growth, aphids can be found on house plants' growing tips, leaf axils, leaves (mainly on the underside) and flower buds. In addition to the actual insects, patches of honeydew and larvae, it is frequently also possible to spot accumulating cast off skins (white) on leaves' upper sides.
Visible effects of infestations include dark patches (black sooty mould), curled/ distorted leaves/ flower buds and stunted/ distorted overall plant growth.
Dealing with Infestations
While it is often possible to deal with infestations in gardens or greenhouses by introducing natural predators, such as, for example, parasitic wasps, ladybirds, lacewing or hoverfly larvae, this is obviously not a viable option for indoor plants. There are, however, many effective measures to get rid of these pests.
Naturally, the first step is to isolate infected plants in order to prevent the infestation from spreading to as yet unaffected plants.
Minor attacks can often be dealt with by simply squashing the insects between the fingers, or by spraying the plant with room-temperature water and/ or using a damp, soft cloth to gently wipe insects, eggs and larvae off the plant.
Dabbing aphids with a cotton swab doused in rubbing alcohol (should be repeated every two or three days) is also very effective, although this method should be used with caution, as covering large areas of a house plant with rubbing alcohol will result in tissue damage.
Giving the plant a wash with a washing up liquid (two teaspoons) and water (4.5 litre; 1 gallon) solution (carefully rinsing with clear water afterwards) also helps, as will spraying the plant with a citrus solution.
Insecticidal soaps, which typically consist of potassium or sodium salts, are also very effective and, if used as directed, also do not harm pets or humans.
Should an infestation be really stubborn, it may become necessary to reach for more drastic measures in the shape of chemical pesticides. There are two main types of pesticides. The first group is based on natural ingredients, including fatty acids, pyrethrum, urea/ mineral lattice, plant extracts, plant oils and/ or fish oils. Typically acting on contact, treatment must be extremely thorough and will last for short periods only, meaning applications need to be repeated several times.
The second group of pesticides uses synthetic ingredients. Synthetic pesticides using lambda cyhalothrin or Deltamethrin act on contact, making repeated thorough applications necessary. Systemic pesticides predominantly use acetamiprid or thiacloprid and are very effective, although caution is advised. It should be noted that acetamiprid may be used on ornamental plants only.In any case, reading and carefully following instructions and ensuring that the chemical pesticide used is suitable for the plant/ s to be treated is of utmost importance.