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Leaf-eaters

September 7, 2019

Young Yellow Box tree

While inspecting with dismay the considerable damage done by deer (Sambar and Fallow Deer) to revegetation plantings at the back of our place (bark stripped, defoliation and broken branches, even on well-established plants), we came across a young Yellow Box, Eucalyptus melliodora (see photo at left), with extensive damage of a different sort. Most of its leaves were severely skeletonised in patches, and in some cases eaten right through. A quick inspection of the foliage revealed many interesting-looking sacs hanging from branchlets in the tree (photo below). These we assumed were associated wih the leaf damage, and later discovered that they belong to the Ribbed Case Moth, Hyalarcta nigrescens.

Actually most of the sacs seemed to be old and inactive – one we dissected had only a dry pupa case inside, the moth having flown the coop. On closer inspection of the leaves, we noticed there were numerous much smaller cases (less than 1cm long), and these contained tiny dark larvae actively chewing and moving around, which were clearly responsible for much of the leaf damage.

The wingless female Ribbed Case Moths remain in the case for life, and lay their eggs in there. Hatched male larvae (caterpillars) leave the case and feed on the surface of eucalyptus leaves. They construct silken cases which they enlarge as they grow. Eventually they pupate and leave the case as a small hairy moth with transparent wings, as can be seen on the BowerBird website.

Larval case

Ribbed Case Moth caterpillar


The cases are built of tough silk and are incredibly strong. Unlike those of many other members of the Psychidae (case moth) family, they are not reinforced/decorated with leaves or sticks, apart from a few bits and pieces when small.
 
This young Yellow Box will no doubt survive and soon put on a new flush of growth, unlike some of the deer-damaged plants, unfortunately!

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