Interceptions of Oemona hirta by the United Kingdom on Wisteria plants from New Zealand: addition to the EPPO Alert List
In June 2010, the NPPO of the United Kingdom intercepted a consignment of Wisteria plants from New Zealand because of the presence of an exotic longhorn beetle which was identified as Oemona hirta (Coleoptera: Cerambycidae). This beetle is native to New Zealand where it is a common pest attacking a very large number of woody plants, in particular citrus trees (hence is common name ‘Lemon tree borer’). In June 2010, this consignment of Wisteria rootstocks from New Zealand was delivered to several nurseries in the United Kingdom. In two counties (Worcestershire and Cheshire), living larvae of O. hirta were detected in Wisteria rootstocks and all the plants were destroyed. It is also recalled that in October 1983, a single living larva had been intercepted in a Wisteria plant from New Zealand. As a response to these findings, the NPPO of the United Kingdom conducted a rapid Pest Risk Analysis which indicated that O. hirta could be a threat to a wide range of plant species in the EPPO region, and its addition to the EPPO Alert List was recommended.
Oemona hirta (Coleoptera: Cerambycidae – Lemon tree borer)
Why: Oemona hirta is a common pest in New Zealand which attacks citrus trees (hence its common English name ‘lemon tree borer’) as well as a wide range of woody plants including fruit, ornamental, and forest species. This pest was intercepted by the NPPO of the United Kingdom on Wisteria plants for planting in 1983 and 2010. A rapid PRA conducted by the British NPPO concluded that O. hirta could be a threat to the UK and also to other parts of Europe, and recommended adding it to the EPPO Alert List.
Where: Oemona hirta is a native longhorn beetle of New Zealand, and so far it has only been recorded in this country.
Oceania: New Zealand. Present on both Islands (except in very dry areas), it is recorded mostly from the Northern half of the North Island and around Nelson in the South Island.
EPPO region: Absent. Intercepted by the United Kingdom in 1983, and again in 2010 on plants for planting of Wisteria imported from New Zealand.
On which plants: O. hirta is a highly polyphagous species which feeds on many plants (more than 40 plant genera). In New Zealand, Citrus spp. are the major host plants but many other species of economic importance can be attacked. O. hirta has been reported on fruit crops, such as: Diospyros kaki, Ficus carica, Malus, Prunus avium, Prunus domestica, Prunus dulcis, Prunus persica, Punica granatum, Pyrus, Ribes uva-crispa, Vaccinium, Vitis vinifera ; forest trees and woody ornamentals such as: Acacia, Acer, Aesculus hippocastanum, Alnus, Betula, Corylus, Crateagus, Juglans, Eucalyptus, Euonymus japonicus, Hibiscus rosa-sinensis, Pinus (conifers are mentioned as rarely attacked), Platanus, Populus, Quercus, Rosa, Ulex, Ulmus, Wisteria. In non-cultivated environments, O. hirta is also mentioned as part of the invertebrate fauna of mangrove trees in New Zealand.
Damage: Damage is caused by larvae which bore into the wood of branches and stems. Although living predominantly in branches, larvae can also mine into the trunk of trees. Adults feed on pollen and nectar. The larvae of O. hirta bore long tunnels in woody tissues (both sapwood and hardwood) with side tunnels leading to holes through which frass is ejected. Larval feeding activities can cause wilting and dying of twigs and branches, as well as die-back in tree crowns. Attacked branches are more susceptible to wind breakage. In New Zealand, O. hirta is mainly considered as a citrus pest (e.g. severe damage was reported in Northland and Gisborne regions in the late 1990s), but it can attack other fruit crops or ornamental trees and shrubs. In particular, damage has been reported in the 1990s on apple orchards near Hamilton, vineyards in Hawkes Bay, or persimmon (Diospyros kaki) in the Waikato region. In poplar nurseries, O. hirta may cause damage when it girdles the living stumps used for the production of cuttings.
In most parts of New Zealand, O. hirta requires at least 2 years to complete its life cycle. Eggs (2.0-2.2 mm) are laid singly (from October to January) in leaf and branch junctions, bark crevices, and fresh pruning wounds. During its 2 month’s life, a female can lay approximately 50 eggs. Newly hatched larvae bore directly into the wood. Larvae are creamy white with dark brown mandibles, and full grown larvae can reach 35 mm long. They can be found all year round and remain inside trees for more than a year. Pupation can be observed from June to October and lasts approximately 3 weeks. Pupation takes place in a cell which consists of a short length tunnel blocked with two plugs formed from short strips of wood. In New Zealand, adults emerge from October to January. Adults are slender beetles (15 to 30 mm long) with long antennae and fine transverse ridges on the prothorax. The body colour varies from red-brown to almost black.
Pictures of O. hirta can be viewed on the Internet
Transmission: In the literature, adults of O. hirta are reported to be good flyers, being most active in the morning (from 5 to 7 am) and the evening (from 7 to 9 pm). A peak of flight activity occurs in October and November in New Zealand. However, there is no data on the distance they can fly and on how rapid natural spread might be. Infested plants are likely to transport the pest over long distances, and the UK interceptions on Wisteria clearly demonstrate that such a possibility exits. Due to the hidden mode of life of this insect during most of its life cycle, infestations are difficult to detect during visual inspections (the presence of sawdust may be a sign).
Pathway: Plants for planting of host plant species from New Zealand, cut branches?. There is no evidence that this insect can be transported on wood (it seems unlikely as larvae feed on living plants).
Possible risks: O. hirta is a very polyphagous species and many of its host plants are of major economic importance in the EPPO region; being cultivated as fruit crops (e.g. citrus, pome and stone fruits, grapevine), woody ornamentals or forest trees. Although further studies are needed on the potential of establishment of O. hirta in the EPPO region, large parts of New Zealand have a temperate oceanic climate which is comparable to many parts of Western Europe. It seems that O. hirta has the potential to establish outdoors, at least in parts the EPPO region. There is relatively little information about the control of O. hirta in orchards or nurseries. Control of tree borers is in general difficult. Once larvae enter branches and trunks, chemical control is considered impractical. Research has identified possible biological control agents parasitizing larvae, such as: Xanthocryptus novozealandicus and Campoplex sp. (both Hymenoptera: Ichneumonidae), Apsicolpus hudsoni (Hymenoptera: Braconidae), and Steinernema feltiae. Pruning of infested twigs/branches at appropriate periods (with destruction of pruned parts and protection of wounds) can help to reduce pest populations. If introduced into the EPPO region, O. hirta is likely to present a threat to fruit orchards, forest and amenity trees, as well as to the nursery sector.
EPPO RS 2010/177
Panel review date: -
Entry date 2010-10
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FERA website (GB)
Rapid assessment of the need for a detailed Pest Risk Analysis for Oemona hirta, the lemon-tree borer. http://www.fera.defra.gov.uk/plants/plantHealth/pestsDiseases/documents/oemonaHirta10.pdf
Plant Pest Fact Sheet. Lemon tree borer Oemona hirta. http://www.fera.defra.gov.uk/plants/publications/documents/factsheets/lemonTreeBorer.pdf
HortNET. Horticulture and Food Research Institute of New Zealand. HortFACT by JR Clearwater (dated 1988) Lemon Tree Borer Life Cycle. http://www.hortnet.co.nz/publications/hortfacts/hf401033.htm
New Zealand Farm Forestry Association. Lemon-tree borer. http://www.nzffa.org.nz/images/design/Pests/Oemona-hirta/Oemona-hirta.html