Primefact 1514, Second edition, May 2026
Giant willow aphid (Tuberolachnus salignus) is an established plant pest in New South Wales.
Primary hosts of giant willow aphid are willows (Salix species) with secondary hosts including apples (Malus species), quince (Cydonia oblonga) and poplar (Populus species).
Giant willow aphid is a large aphid that clusters in colonies on the stems of willow trees (Figure 1). It is not usually found on leaves.
Giant willow aphids are relatively easy to see. Clusters of aphids are found on the end of branches of willow and sallow trees (Figure 1) but may also be seen on thicker inner branches (Figure 2).
Damage
Giant willow aphids suck sap from the host tree and produce large amounts of sugary ‘honeydew’. This honeydew rain may attract wasps and other insects or cause slip hazards (Figure 3). Honeydew will contaminate the fleece of sheep sheltering under infested trees.
Bee honey produced by feeding on giant willow aphid honeydew cannot be processed and sets hard. It is sometimes called “concrete honey.”
Colonies of giant willow aphid are frequently characterised by black sooty mould growing on host plant stems and leaves.
Giant willow aphids are not known to carry disease; however large colonies can reduce the vigour of infected host plants. They impact willow health by reducing shoot and root biomass and increasing water use, causing drought stress and reduced growth. Giant willow aphid has reportedly killed old willow trees overseas.
Description
Giant willow aphid is considered one of the largest aphid species known, with adult body lengths measuring 5.0-5.8 mm long. Wingless individuals are mid-brown to dark brown with several rows of distinct black spots on their abdomen. The body is covered with numerous fine hairs, which give a greyish-golden sheen to the abdomen. There is a prominent large dark brown thorn-like bump in the centre of the back and near the back of the body are two smaller black cones. The antennae are less than half the body length (Figure 4).
Lifecycle and behaviour
No males have been recorded in this species. Female aphids are able to reproduce without males and give birth to live young that are genetically identical. During certain seasons aphids can produce hundreds of young in a couple of weeks but more often one aphid produces 5-10 young a day, for 10 to 20 days.
Aphids form dense colonies on trunks and branches of host trees but generally not on the leaves. If disturbed, aphids kick out their long back legs and wave them about.
In Britain, aphids seem to be very active during cold frosts and snow. They spend time leaving their host plant, walking along the ground and over rocks. Hence, winters in Australia are not likely to limit the survival of this aphid.
Spread
Winged forms of giant willow aphid can fly, however flight distance is not known. All forms may be carried by water if they fall from branches into waterways.
In autumn, or when hosts become overcrowded, aphids may leave the host tree and walk quickly along the ground, over rocks and man-made structures such as buildings, fences, footbridges and along handrails in search of new hosts.
Distribution
Giant willow aphid was detected in New Zealand in 2013. It has now spread through most of New Zealand in both the North and South Islands.
In 2014 giant willow aphid was detected in the north of Tasmania and in southern New South Wales and Victoria. It was later detected in Queensland in 2018 and is regarded as an established pest in these locations.
Actions to minimise risk
- Put in place biosecurity best practice actions to prevent entry, establishment and spread of pests and diseases:
- practice “Come clean, Go clean”
- ensure all staff and visitors are instructed in and adhere to your business management hygiene requirements
- monitor your plants regularly
- keep records