Uraba lugens
(eucalypt leaf skeletonizer)

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).

U. lugens was recorded as invasive in New Zealand by Crabtree (1997). In its exotic range it has become a significant pest of amenity trees, particularly Lophestemon confertus (Australian brush box), which is commonly planted in some parts of Auckland City (Kriticos et al., 2007).

U. lugens is found in all states of Australia except the Northern Territory, in areas where the rainfall varies from 500 mm to more than 1500 mm (Campbell, 1962). In Western Australia, it occurs in south-western coastal areas (Kriticos et al., 2007). In Queensland it occurs in coastal areas from Cooktown in the north to the Atherton Tableland, and in southern Queensland (Common, 1990). It is also established in New Zealand, where it was first detected in 1992. As of 2008 it is widespread throughout the Auckland region, and also present in Waikato and Bay of Plenty regions. It is predicted to spread through most areas of New Zealand where eucalypts are grown (Kriticos et al., 2007).

U. lugens is likely to continue to spread within New Zealand, with the potential to reach all eucalypt growing areas of the country, which covers all but alpine areas, and central and western parts of the South Island (Kriticos et al., 2007). Agents of further spread are likely to be movement of plant material or wood containing eggs, larvae or pupae from infested areas. Unassisted dispersal is likely to occur at a slow rate, as adult moths are thought to fly a maximum of one km from their pupation site (Morgan and Cobbinah, 1977).

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.

Reproductive Biology

As is usual with Lepidoptera both males and females are required for reproduction. Potential fecundity ranges from 235-662 (Campbell, 1962). Egg masses contain between 40 and 200 eggs so it is likely that each female lays more than one egg mass. Newly hatched larvae are less than 1 mm in length and are gregarious, skeletonising leaves by feeding on the leaf surface. After around the fifth instar larvae disperse and become solitary, feeding on the entire leaf blade. Mature larvae wander to find a pupation site on the ground or in the tree in bark or leaf litter. A cocoon is spun, incorporating surrounding material for camouflage, in which the larva pupates. Adult emergence and mating takes place during the early hours of darkness (Campbell, 1962).

Thermal requirements and development thresholds (Allen and Keller, 1991):

Physiology and Phenology

U. lugens can have either one (univoltine) or two (bivoltine) generations per year. This seems to be determined to a large extent by climate (Campbell, 1962; Harris, 1974; Farr, 2002) but the position is not clear. Campbell (1962) identified two biological forms of U. lugens: one costal/inland form which is bivoltine, has 11 instars and the eggs are laid in parallel rows one egg diameter apart; and the highland form which is univoltine, with 13 instars and eggs laid in clumps with no intervening spaces (Farr, 2002). In Western Australia, U. lugens has characteristics of both forms (Farr, 2002). In South Australia U. lugens has between 8 and 13 instars (Morgan and Cobbinah, 1977). In its current range in New Zealand U. lugens is bivoltine, with a phenology matching that of U. lugens in Adelaide, South Australia, and eggs laid in parallel rows (Suckling et al., 2005).

Nutrition

U. lugens feeds on a wide variety of eucalypts and related tree species (Morgan and Cobbinah, 1977; Potter and Stephens, 2005), preferring newly mature and mature leaves for oviposition and larval feeding (Morgan and Cobbinah, 1977). Adults do not have functional mouthparts and thus do not feed (Cobbinah, 1978).
 

Detailed studies of parasitoids of U. lugens have been conducted in Adelaide, part of the natural range of the species (Austin and Allen, 1989; Allen, 1990a). Twenty-two parasitoid species were identified, including 11 primary parasitoids, 10 hyper-parasitoids, and one facultative hyper-parasitoid. All are thought to be indigenous to Australia. The primary parasitoids were mostly Hymenoptera, belonging to seven different families (Trichogrammatidae, Braconidae, Eulophidae, Ichneumonidae, Chalcididae and Eurytomidae), with two species of Tachinidae (Diptera) (Allen, 1990a). All immature stages of U. lugens were attacked by parasitoids, with parasitoids killing hosts from the third larval instar onwards. Although Allen (1990a) found that parasitism was high in some individual groups of U. lugens (up to 50%), parasitism accounted for only 5-10% of overall mortality at the sites studied. At least two of the primary parasitoids are thought to be specific to U. lugens (Coteisa urabae and Dolichogenidea eucalypti), and these are currently under investigation as possible biological control agents for U. lugens in New Zealand (Berndt et al., 2007).

An additional five hymenopteran parasitoids of U. lugens in Australia have been recorded by other authors (Austin and Allen, 1989). Irabatha sp. (Ichneumonidae) and Campyloneura sp. (Braconidae) were reared from U. lugens in Queensland by Brimblecombe (1962). Gauld (1984) lists three ichneumonids from U. lugens (Stiromesostenus spp., Campoplex sp. and Pristomerus sp.).

Five invertebrate predators have been recorded feeding on U. lugens. The mite Microsmaris goannae (Erythraeidae) feeds on eggs, sucking out the contents, although only a small proportion of eggs are affected (Campbell, 1962). The predatory bugs Oechalia schellenbergii and Cermatulus nasalis nasalis (Hemiptera: Pentatomidae), and the lacewing Chrysopa edwardsi (Neuroptera: Chrysopidae) were found to be significant predators of U. lugens larvae (Cobbinah, 1978). Crab spider Philodromus sp. (Araneae: Thomisidae) (Brimblecombe, 1962), jumping spiders (Araneae: Salticidae) and Nabid bugs (Hemiptera: Nabidae) (Cobbinah,1978) have also been found predating U. lugens. Pathogens recorded attacking U. lugens include Aspergillus parasiticus and A. flavus (Eurotiaceae), Chaetomium sp. (Melanosporaceae) and Beauvaria bassiana (Moniliaceae) (Cobbinah, 1978). Aspergillus has been recorded as an important regulator of U. lugens populations in the Murray Valley region of Australia (Campbell, 1962).

In New Zealand, Mansfield et al. (2005) recorded one larval parasitoid (Meteorus pulchricornis, Hymenoptera: Braconidae) and two pupal parasitoids (Xanthopimpla rhopaloceros and Anacis sp. (Hymenoptera: Ichneumonidae)) attacking U. lugens. Since that study two additional pupal parasitoids (Ecthromorpha intricatoria (Hymenoptera: Ichneumonidae) and Dibrachys sp. (Hymenoptera: Pteromalidae) have been recorded from U. lugens in New Zealand (Berndt and Kriticos, 2006). The current impact of these parasitoids on U. lugens in New Zealand is unknown, although it appears to be minor (LA Berndt, Scion, New Zealand, personal observation, 2008).

Animal feed, fodder, forage

• Invertebrate food

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).

In New Zealand, U. lugens cannot be mistaken for any other species. There is one other related species, Uraba deplanana Walker, present in Australia (Edwards, 1996).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

On discovery of U. lugens in New Zealand, the Ministry of Agriculture and Forestry, Biosecurity New Zealand (MAF BNZ, the government organisation with responsibility for new incursions) conducted a delimiting survey and treated infested trees with insecticide in an attempt to eradicate the insect (Ross, 2000). Ongoing surveys in the vicinity were conducted over the following four years (Ross, 2001). Following the second incursion of the pest in Auckland, NZ, in 2001, MAF BNZ followed the same procedure of surveying and insecticide treatment, with the addition of a large scale trapping programme using a synthetic pheromone when the affected area was found to be in the order of 11,000 ha (Thompson, 2003). Due to the large area covered, eradication attempts were not pursued but movement controls were put in place to help slow the spread of the pest (Ross, 2003). Recommendations for the use of selective insecticides for the control of U. lugens have been developed (Mansfield et al., 2006), and stem injection methods are under development for the treatment of individual trees (S Gous, Scion, Rotorua, New Zealand, personal communication, 2008). Biological control is also under development (Berndt et al., 2007).

Little information is available on the economic impacts of U. lugens in its natural range in Australia.

New Zealand: Scion (New Zealand Forest Research Institute Ltd), Private Bag 3020, Rotorua, http://www.scionresearch.com

02/05/08 Original text by:

Lisa Berndt, Ensis Forest Biosecurity and Protection, Scion, 49 Sala St, Private Bag 3020, Rotorua, New Zealand