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Thứ Ba, 28 tháng 4, 2015

Sap sucking insect plays role in changing the colour of eucalytps - WA today

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Pictures of lerp in Canberra.

Pictures of lerp in Canberra. Photo: Supplied

One of the great features about living in our bush capital is the four distinct seasons we experience.  

As we travel around our beautiful city, the tell-tale signs of autumn are everywhere. Along with the truly spectacular colours on show, you may have also noticed some eucalypts changing colour.

We have more than  750,000 trees which form the stunning visual backdrop that is our urban forest. Outside of the city limits, we have our beautiful mountain landscape. 

The common species among these spectacular trees are the eucalypts. With the changing season a number of these eucalypts are now suffering from the seasonal effects of a tiny native insect, psyllids.


 This insect infestation can give the appearance the tree is changing colour or even dying.

As the years roll by, I've come to appreciate how nature has designed a role for everything and everything has a role in nature – including sap sucking insects.

Psyllids resemble tiny cicadas. During their larval phase they develop a thirst for syrupy eucalyptus sap, sucking up the nutrients from the eucalypt leaf turning it a golden brown colour. 

It's during this phase of their development they develop a sweet, protective white coloured shelter known colloquially as a lerp. The lerp in turn becomes a sweet tasting morsel for our birdlife. 

The circle of life continues with one species relying on another.

Lerp infestations are a seasonal influence and will not normally kill affected trees. A dilemma arises with extensive and repeated defoliation through heavy lerp infestation year after year. This repeated infestation can lead to dieback or even the death of some trees.

The red gum trees planted in the median strip of Northbourne Avenue more than 60 years ago were removed in the early 1980s because they had been severely affected by repeated lerp infestation over many years.

We do not attempt to control lerp because of the large number of trees involved, however the use of an insecticide can control the insects. 

The difficulty with using an insecticide is it can also kill beneficial organisms like predatory wasps which are a natural form of lerp control.

The next time you find yourself marvelling at the changing colour of our eucalyptus forest, ponder the role a sap sucking insect is having in making our bush capital the special place it is.

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