Alison’s property and field trial near Rotorua. Left: evidence of a larval activity, frass is pushed out of the tunnel as the insect larva tunnels into the trunk. Right: Alison cleaned away the frass to reveal the entrance and the damage done to the outer bark. (Photos courtesy of Alison Bentley.)
Turns out, New Zealand’s native puriri moth (Aenetus virescens) loves hazelnut trunks too. Originally thought to be lemon borer, seven of the 62 hazels in Alison Bentley’s trial developed these signs of incursion.
Alison works to organic principles and didn’t use pesticide to kill them. On one tree where the burrow was low on the main trunk, she amputated below the burrow, the tree re-sprouted and she chose three leaders to form the new growth. On others, no action was taken, and the larva didn’t kill the tree, but slowed it down.
Murray Redpath, who lives in the Bay of Plenty, has a lot of experience with puriri moths in his orchard. His property is surrounded by native bush, and at night the puriri moths invade, apparently loving all the exotic trees.
Puriri moths are endemic to the North Island, so they were a novelty for the South Island members. Normally they complete their life cycle in native plants like puriri trees, putaputaweta and kohekohe, but clearly they have taken to the introduced plants like moths to a candle.
Below is the link to the Landcare website which has photos of the larvae inside the trunk of trees (not hazels). The extent of the burrows demonstrates why it is so difficult to kill the larvae, PLUS the larva creates a cap to seal the tunnel while it pupates. [Ed: the photos are copyrighted so I couldn’t copy them over for easy viewing.]
https://interestinginsects.landcareresearch.co.nz/taxa/99ebf990-871a-4515-90e5-a9a93ada8637
Another annoying fact, from the human perspective, is that the caterpillar spends between 5-7 years in the trunk before emerging as New Zealand’s largest moth.
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