Hemiptera : Psyllidae, Triozidae

psyllid-adult-800x451px-credit-denis-crawford

Image above: adult Lilly Pilly Psyllid on leaf covered in pit galls
(image courtesy of Denis Crawford)

Psyllids (pronounced ‘sillids’) are sap-sucking insects related to aphids, whiteflies and scale insects. The most common Psyllids in gardens are members of the families Psyllidae and Triozidae, and there are about 400 species that occur in Australia.

Australia has a unique group of Psyllids that produce sugary waxy coverings known as ‘lerps’, which are common on gum trees.

There are other Psyllids that cause galls to form on the leaves of gum trees, as well as the notorious Lilly Pilly Psyllid, which cause gross distortions of lilly pilly leaves. There are also ‘free-living’ Psyllids that don’t form galls or lerps.

Best Treatment for Psyllids

Psyllids are tiny sap-sucking insects that can cause considerable damage to some plants. The best thing you can do is keep an eye on susceptible plants, so that you can spot an infestation in its early stages.

Lilly Pilly Psyllid is the most problematic of these insects because this pest can make a real mess of a lilly pilly hedge. Pruning out the pest is effective but can be unsightly. Lilly Pilly Psyllid really takes hold in unhealthy plants, so water your Lilly pillies appropriately and use a slow-release fertiliser. Avoid giving too much nitrogen fertiliser because that will promote lots of flush growth, which just encourages the pest. Selecting the right (resistant) species of lilly pilly to plant allows you to avoid the problem entirely.

Lerp-forming Psyllids on gum trees are very common. A large tree is not in any danger from these insects, but a sapling gum can look unsightly. You can simply wipe off the lerps along with the psyllid nymphs underneath to prevent the insects causing further damage. Gall-forming Psyllids can be ignored as they will not seriously damage a gum tree.

Tomato Potato Psyllid is a potentially devastating pest that arrived recently in Western Australia. So far it has not been found in eastern states. Western Australian gardeners should contact the Western Australia Department of Primary Industries and Regional Development for more information on what chemicals are currently permitted to help control Tomato Potato Psyllid.

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Image above: leaf infected with Lilly Pilly Psyllid eggs and nymphs
(image courtesy of Denis Crawford)

What are Psyllids &
How to Get Rid of Them

Psyllids are also known as ‘jumping plant lice’. That name comes from the ability of adult Psyllids to catapult themselves into the air to escape from predators. Their leap is unique in that they rotate rapidly forwards, like a tumbling gymnast, many times per second as they spring upwards.

Many species of psyllids form ‘lerps’ on gum trees, and they may occur anywhere in Australia. Some psyllid species only feed on specific species of gum trees. Psyllid nymphs form the lerps - a white, sugary, waxy covering - from their own liquid excretions as protection from desiccation and predation.

Lilly Pilly Psyllid (Trioza eugeniae), also known as ‘Pimple Psyllid’ feeds on several tree species of three allied genera known commonly as ‘lilly pillies’. The insect is found in eastern Australia from South Australia to north Queensland.

The exotic Tomato Potato Psyllid (Bactericera cockerelli) is a recent arrival in Western Australia, and so far, is confined to that state. It is a ‘free-living’ psyllid that does not form galls or lerps.


Description

Adult psyllids resemble tiny cicadas with their clear wings in an inverted ‘v’ over their bodies. Adult psyllids are usually about 2 – 3 mm in length.

Lerp-forming Psyllids

Psyllid nymphs are miniature versions of the adults but without wings and hidden under the ‘lerp’. The appearance of a lerp varies between species, from simple sugary cones, shells and scales to intricately woven baskets and fans. The common name of these species usually describes the lerp (e.g., White Lace Lerp or Brown Basket Lerp).

Lilly Pilly Psyllid

The adult Psyllid has a dark brown body and clear wings. Eggs are yellow, elongated, and about 0.5 mm long. Lilly Pilly Psyllid nymphs are soft, flattened, scale-like, pale creatures about 1 mm long.

Gall-forming Psyllids

Nymphs are hidden inside galls. Common galls on eucalypt leaves caused by the psyllid Schedotrioza are large spherical, red and green distortions.

Free-living Psyllids

Nymphs are miniature versions of the adults but without wings. Nymphs may exude waxy material. Eggs are usually yellowish.

Tomato Potato Psyllid

The adult is brownish with pale markings, and a broad white band on the abdomen. Nymphs are yellowish, oval-shaped, and flattened with red eyes. Older nymphs are fringed with hairs.

Life Cycle

Psyllids pass through a life cycle of gradual metamorphosis – egg, nymph, and adult.

Lerp-forming Psyllids

Adult females lay eggs on leaves, either singly or in batches. They may lay several hundred eggs over their lifetime. Some species like to lay eggs on young leaves, while others prefer mature leaves. First instar nymphs (‘crawlers’) hatch and crawl to a suitable feeding site, begin feeding and start to build their lerp. Larvae pass through five instars under their ever-expanding lerps, before emerging as tiny winged adults. There are usually several generations per year.

Lilly Pilly Psyllid

Adult females insert their eggs in the margins of freshly expanding leaves. Hatching nymphs move to a suitable position on the underside of a leaf and begin feeding. After the first moult, a shallow pit begins to form under the nymph, which increases in size as the nymph goes through further moults. After the final moult an adult psyllid emerges, and the cycle begins again. Lilly Pilly Psyllid can only complete its life cycle on expanding leaves, not mature leaves.

Gall-forming Psyllids

Adult females insert groups of eggs into leaves. Nymphs hatch and burrow into the leaves, which causes galls to form. Each gall on a leaf contains one nymph. Eventually the nymphs reach adulthood and emerge from the galls.

Free-living Psyllids

Eggs are laid on the growing shoots of host plants. Nymphs hatch and pass through five growth stages before adulthood. Adults and nymphs at various growth stages are seen together feeding on the green shoots of plants.

Tomato Potato Psyllid

Eggs are laid on leaf edges or the underside of leaves. Nymphs hatch and pass through five growth stages before adulthood. Nymphs and adults are usually found together on leaves. There are several generations per year.

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Image above: pit galls on Waterhousea floribunda leaves
caused by Lilly Pilly Psyllid
(image courtesy of Elise Dando)

What Plant are Impacted by Psyllids

  • Lerp-forming Psyllids: eucalypts
  • Lilly Pilly Psyllid: Lilly pillies especially Syzygium paniculatum and Waterhousea floribunda.
  • Tomato Potato Psyllid (W.A. only): tomato, potato, capsicum, tamarillo, eggplant and sweet potato. 
  • Gall-forming Psyllids: eucalypts.
  • Free-living Psyllids: native plants, especially wattles and gum trees, occasionally kurrajongs and grevillea. Some free-living Psyllid species may also attack murraya hedges.
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Image above: pit galls on fresh new growth of Lilly Pilly

Symptoms of Psyllids

Lerp-forming Psyllids

A light infestation of lerps usually results in a motley appearance to leaves and/or purple patches on leaves. Some sooty mould may form on excess sap excretions. Plants that have already been stressed in some way, for example by drought, are particularly vulnerable to psyllid damage. A severe infestation may cause excessive defoliation, which leads to a decline in tree health and growth and, in extreme circumstances, tree death.

Lilly Pilly Psyllid

Nymphs cause pit galls on the underside of flush growth leaves of lilly pillies, which cause corresponding pimply distortions on the upper side of leaves. Severe infestations cause extreme leaf distortion and stunting of plants. Attacks are very unsightly but not fatal.

Gall-forming Psyllids

Obvious woody galls on the leaves of eucalypts. They can be ignored or just picked off if you find them unsightly.

Free-living Psyllids

Colonies of tiny insects congregating on young shoots of plants. Waxy secretions, sooty mould. Shoots and leaves may be deformed.

Tomato Potato Psyllid

Upward rolling of leaves, new foliage tinged with purple and stunted growth.

How to Prevent Psyllids Appearing

Monitor

  • Keep an eye on your trees to detect infestations early. Look for lumps and bumps forming on eucalypt leaves, especially of young trees.
  • Check the flush growth on lilly pillies regularly. Look for pimply distortions on leaves.

Prevent

  • Stressed plants are more susceptible to insect attack, make sure your trees are watered and fed regularly with Yates Dynamic Lifter Soil Improver & Plant Fertiliser.
  • Psyllids may be attended by ants seeking honeydew, which may drive insect predators away. Stop ants climbing trees by banding the trunk with horticultural glue.
  • Lerps can be wiped off with a damp cloth. This is an effective treatment of sapling gum trees. Heavily infested branches can be pruned, and the tree fed and watered to promote new growth.
  • Carefully check plants at your nursery before buying.
  • Grow less susceptible species of lilly pilly, such as Acmena smithii and Syzygium luehmannii.
  • Prune off the worst of the Lilly Pilly Psyllid damage to prevent another generation.
  • Prune off colonies of free-living Psyllids.

Natural Enemies

  • Predators such as birds, spiders, lacewings and ladybirds.
  • Parasitic wasps.

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