PEST
 
   NAME
     Psyllid, Lerps (General)
     Various Species
 
   ORDER
     Hemiptera
 
   FAMILY
     Psyllidae

Description of the Pest
There are many types of psyllid, Lerps are one type. All are sap sucking insects and the adults have two pairs of wings that when closed form a roof-like covering. The adults are small from 2mm to 10mm long and are poor filers. Generally psyllids and lerps live in colonies that consist of all stages of nymphs.

Lerp nymphs are so called as they secrete a shell (lerp) under which they shelter; feed and the lerp grow to 5mm across. Each species has a distinctive lerp shape and colour. The nymphs remain active throughout all stages and the lerp protects the nymphs from dehydrating. 

Psyllids nymphs do not form a lerp covering but secrete a waxy material on the leaves where they are feeding. They remain mobile, selecting a site on the underside of leaves or on terminal shoots to feed. 

Cottonwood Psyllid (Mesohomotoma hibisci) is a small fleshy brown insect to 6mm long and produces nymphs that exude white waxy material. It feeds in colonies of mixed stages on new growth or leaves from tropical to subtropical regions. It attacks plants in the Malvaceae family particularly Hibiscus tiliaceus.
 
The Laurel Psyllid (Trioza alacris) is a European species where the eggs are laid on the leaf margins and the nymphs make them curl. 

Appearance and Distribution of the Pest
Psyllids are found from the tropics to warm temperate regions, particularly on the coast after a dry or wet period. Distribution is erratic and it is unpredictable which species will be heavily infested. The adults fly to host plants or can be carried on contaminates plants or prunings. High populations decline due to a lack of suitable leaves or a changing weather conditions.  

Life Cycle
These insects have a Hemimetabolous life cycle, ie. When the immature nymphs resemble the adults.
They have a gradual metamorphosis that consists of five nymphal stages and several generations each season, each takes one or two months. The eggs are deposited on leaves and the emerging nymph locates and feed on the leaf vein, then producing a waxy cover. The adults emerge from these covers to commence a new cycle. The abandoned lerp remains on the leaves for some time.

 Brown Lace Lerps	 Sugar Lerps

Period of Activity
They are active from spring to autumn preferring new growth and a heavy infestation occur during autumn as trees recover from previous attacks. Larvae may also feed from autumn, through winter, to spring depending on climatic conditions.

Damage Caused
Colonies occur on leaves or new growth sucking the sap and producing honeydew. This in turn is infected by sooty mold. Affected leaves are distorted and disfigured, forming bronze or yellowish blotches where the nymphs suck. These blotches may dry out turning brown and giving the plant an unsightly appearance. Infestations reduce the vigour of the host and repetitive attacks can defoliate a tree.  Secondary infestation of borers occurs as epicormic shoots appear.

Susceptible Plants
There are many species of Eucalyptus that are attacked by psyllids and lerps, Eucalyptus botryoides and Eucalyptus robusta are particularly at risk.  Lillypillies especially Syzygium australae, S.coolminianum and. S. paniculatum are also attacked.

Cultural Control
It is difficult to control this pest when it is 30m up a tree and small plants that are repetitively attacked should be replaced with less susceptible species. The vigour of large trees can be improved through cultural practice, but if the tree produces ample nutritious sap the faster the insect population grows.

Biological Control
Psyllids and lerps are attacked by many natural predators including small birds, spiders, scorpions, assassin bugs, ladybirds and lacewings. The eggs may be infected by the parasitic wasp.
Natural predators make little difference to numbers in heavy infestations.

Chemical Control
Contact sprays are limited due to the protective covering (lerp) and systemic insecticides are only affective on plants under 3m. Nursery stock may be sprayed with systemic insecticides as soon as the pest is detected. Large trees may be injected but normally not necessary, because when the damage is seen it is too late to treat it. 
Note
Always read the label for registration details and direction of use prior to application of any chemicals.