Beetle (Lemon tree borer) Oemona hirta
Species: O. hirta
Binominal name: Oemona hirta
Common name: Lemon tree borer.
Oemona hirta is a native beetle of New Zealand and is a common pest. The adults are slender longhorn beetles which vary from red-brown to almost black and are covered with yellowish white hairs lying flat against the body. The head projects downward and bears two small patches of dense yellowish orange hair between and below the eyes. The antennae are slender and about as long as the body. The thorax is barrel-shaped, narrower than the elytra (wing cases), and bears about 10 irregular transverse ridges with short off-white hairs between them. The elytra are almost parallel-sided for most of their length and have numerous long hairs arising from shallow punctures over their entire surface. Between the elytra where they join the prothorax is a small shield-shaped area of dense yellowish orange hair. The legs are long and covered with short yellowish white hair. Overall length varies from 15 to 30 mm and width at the base of the elytra from 3 to 6 mm.
Oemona hirta is a highly polyphagous species which feeds on many plants (more than 40 plant genera). Citrus spp. is 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. So far it has only been recorded in this country. It is present on both Islands and it is recorded mostly from the Northern half of the North Island and around Nelson in the South Island. It is uncommon in very dry areas.
The damage to plants 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 bore long tunnels in woody tissues (both sapwood and hardwood) with side tunnels leading to holes through which frass (excreta of insects) are 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.
The 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. The larva is white and cylindrical and up to 25 to 40 mm long with gouge-like jaws. Each thoracic and abdominal segment has a swollen transverse ridge. Long brown hairs are present on the prothorax and on the sides of the other two thoracic segments and all the abdominal segments.
Oemona hirta larvae were intercepted by the National Plant Protection Organization of the United Kingdom in imported Wisteria plants in 1983 and 2010. 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.
Photographed mid January
Oemona hirta in rest position
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