Giant Willow Aphid
Giant willow aphid (Tuberolachnus salignus) was first detected in Tasmania on 11 March 2014 at Longford. This was the first record for Australia. Within weeks it was found across much of Northern Tasmania but at only two locations in the south, near Hobart. By April 2014 it had been found in parts of New South Wales and the ACT and subsequently found in Melbourne and Albury. In 2016-17 public reports of this aphid in southern Tasmania became more frequent. It is now widespread across most of Tasmania, although it is has not yet been reported from the Tasman Peninsula or the Bass Strait islands.
Giant willow aphid
Giant willow aphid (GWA) is found primarily on willows, but also sometimes on poplars, where it sucks sap from tree stems and young branches, often forming dense colonies. It remains unclear how and where the aphid first entered Australia.
Dense colony of giant willow aphids (image courtesy of Alan Flynn, Ministry of Primary Industries, New Zealand)
Giant willow aphids produce copious amounts of sugary honeydew while feeding. This falls onto branches and structures under willow trees. A black mould then grows on the honeydew. Some dieback of younger tree limbs has been observed where GWA is prevalent.
Sooty mould and dieback on willow trees at Branxholm, infested by giant willow aphid
Giant willow aphids produce copious amounts of honeydew from feeding, which can attract large numbers of bees and wasps, which feed on this sugary liquid, creating a nuisance in localized areas where willows are prevalent. European wasps attracted to the aphid honeydew can increase wasp attacks on beehives.
New Zealand beekeepers have found that when bees feed on large amounts of giant willow aphid honeydew, the honey they make can be hard and crystallized and difficult to extract, reducing yields. In April 2021, the first case of 'concrete honey' in Tasmania was reported (Fig. 1). Beekeepers are urged to monitor willows for this aphid in the vicinity of their hives to reduce the likelihood of 'concrete honey' and hive disturbance by wasps.
Giant willow aphid is easy to spot and difficult to confuse with any other aphid. It is one of the largest aphids in the world (up to 6mm in length), dark grey in colour, with distinctive black spots and large tubercles (Fig. 2). Giant willow aphids build up dense colonies in summer, which persist through autumn (Fig 3). This aphid feeds on the stems rather than the leaves and can persist after the leaves fall.