Each species of conifer aphid has a restricted host range and specific symptoms. Some of the conifer aphids frequently encountered in gardens are listed below.
Note: When searching for aphids, it is easy to confuse them with harmless insects known as psocids or barklice. These aphid-sized insects, may be winged or wingless, are generally brownish-white in colour. They feed on algae and fungal spores and may be abundant on trees affected by sooty mould. They run rapidly over the foliage and stems, unlike slow-moving aphids. Adelgids are usually either associated with galling or are covered in a white waxy substance.
Green spruce aphid (Elatobium abietinum): A small dark green aphid (1.5-1.8 mm long) with red eyes. It feeds on spruces, Picea species, especially P. abies (Norway spruce or Christmas tree), P. sitchensis (Sitka spruce) and P. pungens (blue spruce). It is unusual amongst aphids in that it is active during from autumn to spring. It can be found on spruce throughout the year but the summer months are spent as non-feeding nymphs. These start to mature during August and numbers can gradually build over the following six months. The green spruce aphid is favoured by mild winters which may result in damaging population levels occurring by late winter-early spring. The old foliage develops a pale mottled discolouration and many of these needles fall from the tree during the spring. This species produces honeydew and the resulting sooty mould is often noticed on stem joints. New growth in the spring is unaffected and its bright green appearance contrasts strongly with the discoloured and sparsely foliated older stems.
Juniper aphid (Cinara fresai): This species is of North American origin but is now widespread on Juniperus species in gardens in southern England. It is a large aphid (2.2-4.2 mm long) which varies in colour from pinkish-grey to brownish-grey. The dorsal surface of the body is marked by a darker inverted V towards the head end. It can form dense colonies on the younger shoots and is found from May to October. This species produces honeydew and the resulting sooty mould is often noticed on stems and foliage. Large populations can result in dieback of shoots or even the death of plants. The Gardeners often use the word variety when referring to a specific plant, but the correct botanical term is 'cultivar'. Whichever word you use, it means a distinctive plant or plants, given a specific cultivar name and usually bred to enhance certain characteristics, such as flower or fruit size, colour, flavour or fragrance, plant size, hardiness, disease resistance, etc. Additionally, it is worth knowing that, botanically, variety has another meaning - it refers to a naturally-occurring distinct plant that only has slight differences in its looks. For example, Malva alcea var. fastigiata differs from typical plants by having an upright habit.
Cypress aphid (Cinara cupressivora): This aphid feeds on Cupressus species especially C. macrocarpa, Thuja occidentalis, Chamaecyparis lawsoniana and x Cuprocyparis leylandii. It is 1.8-1.9mm long and yellowish-brown although it appears greyish due to a dense coating of fine hairs. There is a dark stripe running down either side of the upper body, particularly at the head end. It is active from May to November but are most noticable during the early summer. Small colonies tend to develop at the bases of the green shoots, which often become blackened by sooty moulds Transferring young plants from one container to a slightly larger one, where they will have more room to grow and fresh potting compost. This encourages continuous, healthy growth.
Cedar aphid (Cedrobium laportei): A small aphid (1.5-2 mm) long and greyish-brown with a paler mid-dorsal stripe running from the head end. It feeds on cedars including Cedrus atlantica, C. deodora and C. libani. Dense colonies can occur at the bases of the leaves during May and June, this can result in the affected leaves being shed. This aphid excretes large quantities of honeydew and sooty mould frequently develops, both on the tree and on the ground underneath.
Large cedar aphid (Cinara confinis): The largest populations occur in June-July but this aphid is active on Cedrus and Abies species from March to October. A very large aphid at up to 7.8 mm long they are greenish black or dark brown with a double row of dark spots on the upper surface of the abdomen. The foliage can become sticky with honeydew and blackened by the growth of sooty moulds. It can become active in winter on Abies brought indoors for use as Christmas trees.
Black spruce bark aphid (Cinara piceae): The adult aphids are large (5-6 mm in length) and sometimes mistaken for spiders or beetles. The adult aphids are shiny black with reddish-brown legs, while the nymphs have duller greyish-black bodies. They suck Sap is a fluid that circulates through a plant's vascular system, in a similar way to blood moving through our veins. Phloem sap carries the sugars produced in the leaves by photosynthesis down to roots and other storage organs, as well as carrying minerals and hormones. Xylem sap is watery and transports nutrients absorbed by the roots upwards to the rest of the plant. Some plants leak sap from wounds or pruning cuts, and this is known as bleeding.
Bark is the outermost layer of woody plants (trees, shrubs and woody climbers). It is several cells thick and provides protection against physical damage, disease and environmental stresses. Bark comes in a wide variety of colours and patterns, and these can help gardeners when identifying plants. The fissures and crevices of bark on older plants also creates valuable habitat for many garden creatures as well as lichens and small plants.
Grey pine needle aphid (Schizolachnus pineti): Dense colonies of this 1.2-2.5 mm long aphid can occur on the undersides of the mature leaves of Scots pine and other Pinus species. The aphids are coated with a greyish-white wax and they are present from May until the autumn. Large populations may cause yellowing of the foliage.