Elm Zigzag Sawfly
This pest has spread rapidly throughout Europe!
- First recorded in Europe in 2003
- How it came to be in Britain is not known
- Identified in Britain in 2017 near Dorking in Surrey.
- Since June 2018, further reports have come in from south east England and the east Midlands
- It feeds only on Elm trees hence the name
Life Cycle/Damage caused
- Reproduction is exclusively done by parthenogenesis, as no males have been recorded.
- Eggs are laid by the adults into the serrations at the edge of elm leaves and the larvae hatch within 4-8 days.
- The larvae proceed to feed on the leaf tissues between the main leaf veins and whilst small, they produce a characteristic ‘zigzag’ pattern of feeding damage.
- During the later stages of infestation, the feeding damage to the leaves becomes more extensive and some of the smaller veins are eaten.
- The larvae has 4-7 growth stages), this lasts for about 15-18 days.
- After 15 – 18 days they build either a loose silk cocoon on the underside of a leaf, or later in the year, a stronger solid-walled cocoon that will protect the sawfly over the winter.
- During the summer, the adult sawflies emerge from the cocoon completing their life cycle. This normally takes a maximum 7 days within the normal temperature range.
- If the weather is unusually warm 24oC and above. This can significantly slow the completion of its life cycle to 23 – 24 days.
- If the weather is unusually cool e.g. 11oC . This can significantly slow the completion of it’s life cycle to as much as 85 days.
- During the summer it is known that multiple generations are produced. However the average amount for a typical summer is not known.
The Risk Posed by Elm Zigzag Sawfly
Their is a question mark as to what the level of risk is to Elm trees. It is believed that the British climate slows the life cycle of this pest which is an advantage in minimising the damage it can cause. On the continent where the weather can be much hotter it has caused extensive damage. It is assumed that the spread of this pest will continue throughout the UK.
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