Giant Willow Aphid: A Mysterious Bug Which Disappears in Spring and Reappears at the End of Summer

The Royal Horticultural Society (RHS) is asking for sightings of the giant willow aphid (Tuberolachnus salignus) so that researchers can learn where it goes and how it interacts with garden plants.

It is one of the UK's largest aphid species, measuring close to 6mm long and with a distinctive shark-like fin, and an RHS team of entomologists is asking gardeners to send pictures if they see it.

The team wants to figure out why the "mysterious" and "interesting" garden bug has a fin, as well as learn more about its lifecycle and which plants may host it.

Have you seen this bug?

(Photo : horror by numbers/Unsplash)

From July to February, giant willow aphids are frequently seen, with a peak in sightings in the autumn.

They are found on willow, as the name suggests, but the RHS wants to know if they are found on other plants, especially if they are seen between February and the end of May, as per The Guardian.

The insects are visible to the naked eye, but they sometimes hide in bark crevices to avoid predators.

They are typically found on tree stems and branches, and they do not cause unsightly damage to host plants, which can withstand the delicate feeding of these insects.

Colonies of this aphid were discovered in May 2022 on a quince tree (Cydonia oblonga) in Hertfordshire, a new host for this aphid.

They were previously found primarily on willow and on occasion on other trees such as apple and poplar.

Dr. Andrew Salisbury, the RHS principal entomologist, stated that the discovery of giant willow aphids on quince, a previously unknown host, at a time of year when they are rarely seen, only adds to the myriad of mysteries surrounding this fascinating and sometimes elusive aphid.

Gardeners are being used as an untapped resource in science experiments more than ever before.

Private garden space in the United Kingdom covers approximately 728,900 hectares (1.8 million acres), so its potential as a wildlife haven is significant.

Gemma Golding, the RHS's chief ecologist, recently asked gardeners to send photos of interesting "weeds" in the hope that rare wild plants will be discovered growing in new places.

In recent years, the RHS has taken a greater interest in wildlife-friendly gardening, with meticulously maintained and sterile gardens becoming a thing of the past.

The RHS, which organizes the Chelsea Flower Show, has changed its stance on previously unwanted garden visitors, announcing last year that slugs and snails would no longer be considered pests.

Although gastropods were the most commonly reported garden visitor, Britain's leading garden charity stated that they should be considered an important part of the garden ecosystem.

You're just as likely to get advice on how to entice nature into your garden as you are to see perfectly pruned roses at RHS flower shows.

Also Read: Aphids Land on their Legs after Falling from Plants

Biological control of giant willow aphid

Scion entomologists identified and tested a biological control agent for giant willow aphid, which was approved and released in New Zealand.

The giant willow aphid (Tuberolachnus salignus), also known as GWA, was first discovered in New Zealand in 2013.

Aphids feed on willow sap, causing damage and even death to the trees.

Willows are widely used in New Zealand for slope stabilization, flood protection, crop and livestock shelter, fodder, and as a source of pollen and nectar for honeybees in the early spring.

Aphids also secrete a lot of honeydew, which attracts insects like honeybees and pest wasps.

Honey made from honeydew is granular and cannot be extracted from the comb, and wasps pose a threat to bees.

Excess honeydew also promotes the growth of sooty mold on and beneath infested trees.

Biological control, in which natural enemies control a pest, is a low-cost, long-term, and environmentally friendly method of pest control.

While GWA has few natural enemies in New Zealand, Scion scientists discovered parasitism by the parasitoid wasp Pauesia nigrovaria in natural populations of GWA in California.

The parasitoid wasp lays an egg in the aphid, which hatches into a larva that eats and eventually kills the aphid host.

A new adult parasitoid emerges from the dead aphid in two to three weeks.

Before releasing a biological control agent, extensive testing is required.

The first parasitoids were introduced into Scion's containment in 2017, followed by host specificity testing with non-target aphid species to ensure that the parasitoid only attacked GWA.

Following positive results, an application to the Environmental Protection Agency was approved, and permission to release was granted in December 2019.

Scion and partners released parasitoid wasps as part of a New Zealand-wide community effort.

Scion distributed mated female parasitoids to beekeepers, regional council employees, and others for use on infested trees.

Those involved in the releases, as well as citizen scientists, are now monitoring the parasitoid's survival and spread.

Not only did the tiny wasps survive the winter, but they also multiplied exponentially and spread up to 100 kilometers from the initial release sites.

Normally, a biocontrol agent disappears for a few years while it settles in before showing signs of establishment, followed by a slow spread.