What are Willow Sawflies?

These few summary paragraphs represent the views of the writer, who has no formal qualification in this area but is interested and involved in controlling seeding willowa in Australia.


What is willow saw fly?
sawfly larvae sw.JPGWillow saw fly is a small insect that comes from Europe. There are many saw flies and the scientific name for the willow sawfly currently (2007-08) impacting willows in Australia is Nematus oligospilus. It can progress through the lifecycle of egg, larva, pupa and adult in about 4 weeks and so they can go through between 4 and 6 life cycles in a season. They hibernate over winter in cocoons, mainly in the leaf litter around willow trees. It is the Lava stage that eats the willows leaves and with large populations they can defoliate the willow tree more than once over the growing season. There are currently only female willow sawflies in Australia defoiliation sw.JPGand so they reproduce clonely and there is a research project underway to determine if the different populations share a common genetic source. The research is also looking to see if this genetic source is shared with populations in New Zealand, South America and North America. There is also research in New Zealand and Victoria into the impact that Willow Sawfly may have on willow populations. There is concern that continued defoliations of the tree particularly when the tree is under stress, like during droughts, may result in deaths of large numbers of willows.

  

What are the implications of willow sawflies on the need for continued willow control?
Initial research in New Zealand found that if there were successive seasons with 4 or more life cycles of the saw fly willows were found to be dying. However, to date the Victorian DPI research has found no extensive evidence of that happening in Australia.
Is the lack of a natural predator in Australia the reason why willows are weedy here and not in the northern hemisphere? So will the presence of Sawfly curtail the spread of fragile willows and be a long term solution that allows landowners to retain willows in appropriate high risk erosion areas without the issue of them spreading downstream into areas managed for their conservation values
The research into the water usage or willows found that during days of temperatures above 40C willows defoliated and water usage declined. Although the decline was not down to that of river red gums. Will the defoliation by saw flies result in a decline in the water used by willows and allow some of our creeks to flow again.

For a more educated view of willows sawfly and also more information I suggest looking at the reports form the research that has been undertaken.

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