Q: We have a puriri tree in our bush. About a couple months ago it started to die back on one branch. There’s a moth hole in the bark, could this be the cause? Do I need to worry about it? It also looks like there are new shoots coming out of the ground, are they young puriri?
Question from J. Murr, via email
A: The hole in your puriri branch looks like it was caused by a puriri moth larva quite some time ago, probably several years ago. Puriri moth is the largest of all native moths with a wingspan reaching 80-150mm. Females are velvety green with dark markings; the male is smaller and green with white markings. The life cycle from egg to adult can take several years. The female lays eggs in the soil where the larvae hatch and spend the first few months feeding on fungi, sheltering under a cover of silken threads. After a few months they moult and crawl up a tree or shrub to bore a tunnel into the wood sloping slightly upwards for a short distance then turning vertically down the stem. The tunnel entrance is covered by a silken web and the larva comes out at night to feed on callus (scar tissue) that grows around the tunnel entrance. Larvae can grow to 100mm long and live in these burrows for anything from eight months to several years. When fully grown the larva pupates in the vertical tunnel and four to five months later emerges as an adult moth which lives for a week or so, surviving on fat stored from its time as a larva, long enough to find a mate and for eggs to be laid.
Quite a range of trees and shrubs, both native and exotic, can be home for puriri moth larvae. Once the larvae have vacated the hole other insects often move in, including tree weta. Sometimes the damaged tissue in the hole can become infected by fungi which may be the cause of the dieback you observed. I wouldn’t be concerned about this, puriri are perfectly capable of surviving under these conditions.
The shoots you see arising from the ground below the tree are puriri, possibly seedlings, but look to me like suckers growing from the root system. All these are indicators that the tree is still relatively healthy.
Answer by Andrew Maloy (The Plant Doctor)