) 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.
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.
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 (Fig 4).
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.
Further information about the giant willow aphid is available on the
Agriculture Victoria website.
Figure 1. First record of concrete honey in Tasmania in April 2021 (image courtesy of Guy Westmore, Department of Primary Industries, Parks, Water and Environment, Tasmania)
Figure 2. Giant willow aphid (image courtesy of Guy Westmore, Department of Primary Industries, Parks, Water and Environment, Tasmania)
Figure 3. Dense colony of giant willow aphids (image courtesy of Alan Flynn, Ministry of Primary Industries, New Zealand)
Figure 4. Sooty mould and dieback on willow trees at Branxholm, infested by giant willow aphid (image courtesy of Stephen Pryor, Department of Primary Industries, Parks, Water and Environment, Tasmania)