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The small hairy larvae of U. lugens feed gregariously on the upper and lower epidermis, the pallisade tissue and the spongy mesophyll of the leaf but avoid the oil cells and the veins. This feeding habit results in the leaf being ‘skeletonised’, hence the common name of the insect. Larger larvae, from the fifth instar, feed individually and consume the entire leaf blade down to the mid-rib (Cobbinah, 1978). From around the fifth instar, U. lugens larvae retain their moulted head capsules on top of their head, creating a distinctive ‘head dress’. Larvae spin a camouflaged pupal cocoon incorporating their own hairs and fragments of surrounding materials. Adult moths are approximately 10 mm in length with a wingspan of 25 to 30 mm. The forewings are dark grey with several dark wavy lines connecting front and rear wing margins (Anonymous, 1979). The hindwings are pale grey-brown.

Recoginition

U. lugens can be detected by searching leaves. Eggs are laid in batches on the leaf surface, and young larvae feed gregariously adjacent to the egg batch after emergence. Oviposition tends to occur mainly in the lower crow of the tree (Morgan and Cobbinah, 1977). Young larvae skeletonise the leaves, making leaf damage easy to detect. Skeletonised leaves often have characteristic patches of cast skins where larvae have moulted before moving on. After the fifth instar larvae disperse and can be found singly, often in the vicinity of abandoned skeletonised leaves. When close to pupation, larvae wander in search of a suitable site. Camouflaged cocoons are formed in the bark or leaf litter and are very difficult to find. A synthetic pheromone has been developed, and can be used for detection and delimiting surveys (Suckling et al., 2005).

Related invasive species

  • Uraba lugens

Related Farm Practice

  • Feeding
  • Damage
  • Defoliation
  • Materials
Impact

U. lugens was first considered a serious pest of natural eucalypt forests in Western Australia in 1983 when the first severe outbreak occurred there (Strelein, 1988). Prior to that it was widely known as a pest of eucalypt forests in eastern Australia (Campbell, 1962;Harris, 1974). As these natural forests are or were managed for timber production, it is considered an economically important pest in its native range. Damage to amenity trees is also a common problem, although few trees are killed by this defoliation (Anonymous, 1979).

Has Cabi datasheet ID
55727
Symptons

Early instar larvae skeletonise leaves, which then turn brown, giving the tree a scorched look when damage is heavy. Older larvae feed on the entire leaf blade down to the midrib, which can resemble defoliation.

Hosts

Morgan and Cobbinah (1977) list 149 Eucalyptus species and one Angophora species found to be oviposition hosts, out of more than 250 species surveyed in a field study in Adelaide, South Australia. Not all of the oviposition hosts proved to be suitable larval hosts. That work was part of a wider study in which over 580 tree species were surveyed (Cobbinah, 1978). Significant defoliation events have occurred in natural forests of Eucalyptus camaldulensis, E. calophylla and E. marginata in mainland Australia (Campbell, 1962;Strelein, 1988;Farr, 2002), and in plantations of E. nitens in Tasmania (Anonymous, 1994) although damage is common on a wide range of eucalypt species. E. nitens and E. fastigata are important commercial plantation and farm forestry species in New Zealand, although commercial impacts of U. lugens on these species have yet to be felt. The iconic native species Metrosideros excelsa (pohutukawa) has been recorded as a host in New Zealand, although this seems to only occur through spill-over feeding from near by eucalypts (Potter at al., 2004) and is not significantly impacting these trees. A number of other new host records have occurred in New Zealand since U. lugens arrived in that country, most notably on a range of deciduous Northern Hemisphere species. The most significant damage on these species has occurred on Betula pendula (silver birch), where some trees have been defoliated (J Bain, Scion, Rotorua, New Zealand, personal communication, 2008).
In New Zealand, U. lugens has been recorded on 58 tree species (J Bain, Scion, Rotorua, New Zealand, personal communication, 2008), mainly from the genus Eucalyptus. It is causing significant damage in New Zealand on Lophestemon confertus, which is commonly planted as a street tree in some parts of Auckland. In a laboratory study of larval suitability of 18 highly valued eucalypt species in New Zealand, Potter and Stephens (2005) found E. nitens, E. nicholii and E. fastigata were most at risk.

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