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Number 6
Revised October 1992
By Charlma Phillips, Principal Forest Health Scientist

Lerp insects are psyllids and are close relatives of scale insects (coccids). Like other psyllids, they are sap suckers. Forests Insects No 1 in this series describes the Blue Gum Psyllid which is a "free-living" psyllid. Lerp insects differ from free-living psyllids in that their immature stages (nymphs) construct a waxy scale like covering (a "lerp" or "test") beneath which they shelter and feed.
 
 

Lerps of Cardiaspina spp.

The name 'lerp' is derived from the aboriginal word 'larp', for the thick encrustations of these insects that were often collected for food.
Lerp insects often aggregate in colonies of mixed species as well as mixed stages and it is not unusual to find two or more species on the same leaf at the same time and in the same stage of development.

 
Lerp of Spondyliaspis plicatuloides

 
Lerp, nymph and adults of Lasiopsylla rotundipennis

Lerp insects are mostly rare and inconspicuous, but occasionally and without any obvious regularity, they may suddenly increase enormously in numbers and some time later, just as suddenly disappear. Lerp insects (Cardiaspina densitexta) are responsible for the periodic damage to Pink Gum (Eucalyptus fasciculosa) in areas of the Upper South East – particularly along roadsides. The damage is very noticeable as large numbers of trees turn brown and appear dead. Outbreaks of lerp insects (Cardiaspina albitextura) are also common on River Red Gums (Eucalyptus camaldulensis). There are no records of outbreaks of Glycaspis brimblecombei on eucalypts in South Australia but other species of Glycaspis have been involved in outbreaks on Eucalyptus saligna in other states.
Periodic attacks by lerps on eucalypts reduce their vigour and slow down growth. In some seasons huge areas of forest may be defoliated. The main lerp insects of importance in forestry are Cardiaspina spp. and Glycaspis spp.

Descriptions of the most commonly found lerp insects, together with their main host species and the damage they do, are given below in Table 1.

Life Cycle

Lerp insects all have essentially the same life cycle.
They usually live in colonies of mixed stages. Generation times vary with locality and time of year but most species go through several generations per year.
Each female lays between 45 and 700 eggs. These are laid on stalks plugged into the leaf tissue. Eggs hatch within 10-20 days and the young nymphs or "crawlers" move about the host plant searching for a place to settle. They usually settle within 48 hours of hatching. Once settled they insert their stylets (mouthparts) into the leaf and begin feeding and constructing a lerp, beneath which they will feed and shelter until they become adults. Eggs laid in late summer give rise to nymphs which overwinter in that stage and do not become adults until the following spring.
Lerps are formed from the honeydew excreted by the psyllid. In free-living psyllids the honeydew produced remains in liquid form but in lerp insects it hardens on contact with air to form the lerp. Lerps vary enormously in size, shape and design. They may be simple cones, univalves, bivalves or intricately woven basket or fan shapes. Each species has its own characteristic shape.
Nymphs pass through five stages or moults before becoming winged adults. At every moult the insect withdraws its stylets fro the leaf and selects a new feeding site. The new site is usually within the existing lerp but occasionally the insect moves to a new site and constructs a new lerp.
The whole life cycle takes approximately 1-2 months but may be longer, depending on temperature.

Damage

Lerp insects rarely cause the death of trees although defoliation may be severe and there may be some dieback. In some cases other insects move in to attack the weakened tree and the tree subsequently dies.

Periodically there are outbreaks of lerp insects, in particular Cardiospina spp. These outbreaks often last for 2-3 years with several cycles of defoliation and recovery. A feature of these outbreaks is the unacceptable brown appearance of the trees, often over large areas.

There are several theories as to the cause of outbreaks of lerp insects.

One theory suggests that outbreaks are associated with weather induced stress in the tree – usually rainfall (either too much or too little) - which results in changes in the quality of food the insects eat. For example, in times of drought or flooding there is an increase in available nitrogen in the leaves and this in turn means better survival of young insects.

Other theories suggest outbreaks occur when certain conditions combine to provide an environment that is just right for the insect to rapidly increase in numbers. These conditions include ineffective natural control and the abundance of leaves of the right age and quality for maximum growth and survival of the insect. Such conditions often apply in the season following that in which the trees were stressed. Persistent outbreaks often occur in low lying areas where both young and old trees are present.

Feeding by lerp insects causes discoloration of the leaf tissue. In some species no damage is obvious until the nymph reaches the 5th instar. In other species, leaves change colour from green to purple to red around the feeding site and then to brown as the leaf dies. Premature leaf fall is also common with lerp infestations.

The damage caused by individual species is given in Table 1.

Control

Controlling outbreaks of lerp insects is not usually practical and may be difficult to achieve. In general, lerp insects will be adequately controlled sooner or later by natural enemies.

Physical control:

This is not practical as infestations are usually on large trees.

Natural control:

Predators include birds such as honeyeaters, pardalotes, parrots, silvereyes, sparrows and willy-wagtails; other insects, including hoverflies (syrphids), ladybird beetles and lacewings; spiders, mites and lizards.
Parasites include tiny, black Encyrtid and Eulophid wasps. Parasites may reduce population numbers by 50-100%. They are more numerous when population numbers of lerps are high.

Chemical control:

Systemic insecticides, such as dimethoate, are the most effective chemicals to use against sap sucking insects but if attacks are on very large trees spraying is not possible and trunk injections may do more damage than the insect itself. If trees are small they can be sprayed with a mixture of nicotine sulphate + white oil or malathion + white oil but this is not feasible over a large area.

NOTE: When deciding if control is necessary it is important to make sure that the insects are still present under the lerps – often by the time damage is noticed, the lerp insects have become adults and only the empty lerp shells remain.

Summary

When to look:
All year. Make sure insects are still present under the lerps as lerps remain on the leaves long after the insects have gone.

Where to look:
On mature and young mature foliage.

What to look for:

• Trees taking on a brown, dead look.
• Patches of purple, red or brown on leaves.
• Lerps on leaves, often elaborate designs.
• Sooty mould on the leaves.
• Premature leaf fall.
   

For further information please contact PIRSA Forestry

Disclaimer: While this publication may be of assistance to you, the government of South Australia and its officers do not guarantee that it is without flaw of any kind or is wholly appropriate for your particular purpose. The Government therefore disclaims all liability for any error, loss or other consequence that may arise from you relying on any information in this publication.