Eucalyptus leaf-blister sawfly mines

Description:

Pale creamy-brown papery tents of various shapes tightly stretched across the upper surface of gum (eucalyptus) leaves. Some of these had a central raised patch like a blister. The patches were so thin that they looked like a part of the leaf was involved but there was not much obvious damage to the leaves. From afar the tree looked like someone had splashed khaki-coloured paint all over it.

Habitat:

Eucalyptus trees of various species

Notes:

These paper thin patches are coalesced mines of the larvae of a small Australian wasp. The eggs are laid on the underside of leaves, the larva tunnels through leaving the lower leaf surface intact but eating the leaf tissue until only a papery thin cuticle is left. This forms the cover for several mines which join together. It takes about 4 weeks and 10 days from the start of the mine to emergence of the adult. Pupation occurs when the larvae spin themselves a silk cocoon which is attached to both surfaces of the leaves. The pupa appears as a raised hump in the centre of the blister ( Pic #1). The adult emerges through an opening cut in the papery cover. The adult seeks to mate straight after emergence - it does not eat and lives for 5 days only !. Rain increases mortality rate as it destroys the mine covers. The sawfly has many generations per year and development continues even if the leaves are removed from the trees. Biological controls are being used - mostly parasitoid wasps. The reference has some interesting information: http://www.nzffa.org.nz/farm-forestry-mo...