Adelgids are true bugs (Hemiptera) closely related to aphids, and like aphids they also feed on plant sap. They are found on conifers and can have complex lifecycles including more than one host. Several species can be found in gardens, any plant damage is often superficial and in most cases these insect can usually be considered part of the biodiversity a healthy garden supports. 

Spruce pineapple gall adelges, Adelges abietis. Found on spruce (Picea) this species causes green pineapple shaped galls up to 20mm long, usually on young shoots. The galling can cause distortion of shoots, affecting the appearance of trees. Yellow, winged adults (gallicolae) leave the galls in late summer and lay eggs, the nymphs soon hatch and overwinter close to buds. In spring the nymphs feed on plant sap but do not cause galls, maturing into light green wingless females (pseudo-fundatrices). These females lay eggs covered in white waxy threads. The nymphs hatching from these eggs induce the galls when they feed at the base of needles. The galls contain numerous chambers within which groups of pale orange nymphs develop.

Douglas fir adelges, Adelges cooleyi. A native of North America which has become widely established in Britain. It alternates between spruce (Picea) and Douglas fir (Pseudotsuga menziesii). It can be most noticeable on Douglas fir where foliage can become encrusted in white fluffy wax, sooty moulds and can become mottled. On spruce the adelgid causes galling which can affect the growth of new shoots. The adelgid lays eggs in the spring on Douglas fir. The nymphs soon hatch and feed on the needles producing large amounts of white wax and honeydew. The adult females are less than 2mm in length and reddish brown to black, both winged and wingless forms occur. In early summer the winged forms migrate to spruce where they produce a generation that overwinters. In spring the overwintered generation induces elongate galls on spruce, this generation matures in the summer producing winged females that migrate to Douglas fir and overwinter, laying eggs in the spring.

Larch adelges, Adelges laricis. This species is only found on larch (Larix) and spruce (Picea). On larch it covers itself in a white waxy material and it can cause the foliage to become discoloured and distorted and a premature loss of needles. On spruce it forms pineapple galls that are up to 15mm long. The blackish nymphs of this adelgid overwinter on young larch shoots, maturing in early spring and laying eggs at the base of leaves. Nymphs from these eggs develop into wingless or winged 1.5 mm long dark green adults. The winged individuals migrate to spruce. Wingless individuals continue to breed on larch and extensive populations can develop, characterised by large quantities of white wax threads and honeydew. Those that migrate to spruce give rise to a wingless generation that produces gall forming individuals in the following spring. Winged individuals mature in these galls in summer and migrate to larches where they lay eggs.

Scots pine adelges, Pineus pini. This adegid produces a white wax which can disfigure Scots pine (Pinus sylvestris) but damage is usually minor. This adelgid overwinters as nymphs that mature into 2mm long dark brown to red adults in early spring. These adults lay eggs which develop into winged or wingless adults by early summer. The winged forms migrate to other Scots pine, whilst the wingless forms produce further generation on the original tree. There can be several generations in a year.

Weymouth pine adelges, Pineus strobi. Very similar in appearance and lifecycle to Scots pine adelges but only affects Weymouth pine, Pinus strobus. Native to North America and now widespread in Europe.

Balsam woolly adelgid, Adelges piceae. This adelgid is found on firs, Abies species. Found on the woody parts of the plant, the white waxy ‘woolly’ areas can become extensive. Large populations can cause buds to fail and twigs to enlarge, a symptom sometimes called gout disease.  This insect is becoming more frequent in Britain.
 

The damage adelgids cause is often minor and can usually be tolerated and treated as part of the biodiversity the host trees can support. Which is fortunate as on large trees they cannot be treated.
Check susceptible conifers frequently so action can be taken before a damaging population has developed.  When choosing control options you can minimise harm to non-target animals by using the methods in the non-pesticide section below. Little can be done to deal with adelgids on tall trees as treatment is only likely to be successful if the entire plant can be reached. Pesticide treatments are likely to kill natural enemies.

Non-pesticide

• Where possible tolerate or accept populations of adelgids as part of the biodiversity in a garden
• Use finger and thumb to squash adelgid colonies where practical
• Encourage predators in the garden, such as ladybirds, ground beetles, birds, hoverflies, parasitoid wasps and earwigs

Pesticides 
The RHS recommends that you don’t use pesticides. Most pesticides (including organic types) reduce biodiversity, including natural enemies, impact soil health and have wider adverse environmental effects.
 
Where you cannot tolerate adelgids, manage them using the information above as your first course of action.
 
Pesticide treatments are likely to kill natural enemies and so reduce the likelihood of natural control and can lead to resurgence of the target animal.

Within this group the shorter persistence pesticides (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife than those with longer persistence and/or systemic action.
 
The pesticides listed are legally available in the UK. This information is provided to avoid misuse of legal products and the use of unauthorised and untested products, which potentially has more serious consequences for the environment and wildlife than when products are used legally.
 
Always follow the instructions on the products. For edible plants, make sure the food plant is listed on the label and follow instructions on maximum number of applications, spray interval and harvest interval.

Homemade products are not recommended as they are unregulated and usually untested.
Be aware that products such as Neem oil are not registered for use in the UK and we cannot advise on their use.

Plants in flower must not be sprayed due to the danger to bees and other pollinating insects.

• Adelgids are difficult to control with insecticides as they are protected their waxy secretions and there are no controls for the gall forming stages. In addition it is only feasible to treat adelgids on trees that are small enough to be sprayed thoroughly; infestations on tall trees have to be tolerated
• Pesticide controls available for these insects are the same as for aphids which can be found here

Inclusion of a pesticide product does not indicate a recommendation or endorsement by RHS Gardening Advice. It is a list of products currently available to the home gardener.

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