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About laurel wilt and the Asian ambrosia beetle

The Asian ambrosia beetle carries the fungus that causes laurel wilt in its mouth parts. The beetle feeds on the fungus. As the beetle tunnels into a tree, it infects the tree with it. 

The beetles mostly live in avocado trees, but can live in several other laurel trees, including bay trees.

Global distribution of laurel wilt carried by the Asian ambrosia beetle

World map showing distribution of laurel wilt

Why laurel wilt is a risk to New Zealand

If laurel wilt established in New Zealand, it would harm our avocado industry.

Laurel wilt invades the tree's system for carrying water from the roots to the leaves (the vascular system). It blocks the vessels and stops water getting to the leaves. It's the lack of water that damages the tree.

Map of New Zealand showing where this pest/disease could establish

How could it get here?

It's most likely the fungus would enter New Zealand with the Asian ambrosia beetle. The beetle is most likely to get here in wood packaging or wood products. It might also come in on nursery stock.

The Ministry for Primary Industries has rules and treatments in place to detect and kill the beetle at the border.

How to identify these pests

Identifying laurel wilt

If a tree is infected, you'll see wilted leaves that have turned a reddish or purple colour. To start with, it may only affect part of the tree, but it can affect the whole tree. Eventually, the leaves will turn brown, but they tend to stay on the branches.

A red bay tree with over half of the leaves a purple colour.
A red bay tree infected with laurel wilt. Over half of the leaves on the tree have turned purple. Image: CC Albert (Bud) Mayfield, USDA Forest Service, Bugwood.org

Identifying Asian ambrosia beetle

You are unlikely to see the beetle itself because they spend most of their lives in their tunnels. Males never leave the tunnels and can't fly.

You may see strings of compacted sawdust at the entrance hole for a tunnel. They can look like toothpicks but they fall apart very easily.

tree trunk with worm-like sawdust protrusions
Sawdust strings protruding from the trunk of a tree. Image: with permission from Jiri Hulcr, University of Florida.

The adult beetles are:

  • small (2mm to 3mm long)
  • slender
  • brown-black in colour.
Top view of dark-brown beetle
Top view of an adult female ambrosia beetle. Image: © Lyle J. Buss, University of Florida.
Side view of a dark brown coloured beetle
Side view of an adult female ambrosia beetle. Image: © Lyle J. Buss, University of Florida.

Eggs are laid in the tree and the larvae live in the tunnels. You're only likely to see them if you cut down the tree.

What to do if you find laurel wilt or the Asian ambrosia beetle

If you think you've found the beetle, or your avocado tree has reddish or purple leaves:

  • photograph it
  • capture the beetle, if possible
  • call us on 0800 80 99 66 

 

Note: This information is a summary of this disease's global distribution and potential impacts to New Zealand.

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