Phoracantha semipunctata, the Australian Eucalyptus longhorn, is a species of beetle in the family Cerambycidae. Native to Australia, it has now spread to many parts of the world, including practically all countries where tree species of Eucalyptus have been introduced. It has been classified as an invasive pest species of Eucalyptus outside Australia.
Within Australia, Phoracantha semipunctata primarily seeks for decaying trees and branches which have been critically impaired due to natural disasters. In other regions of the world, it inflicts critical damage upon introduced Eucalyptus trees. However, the damage inflicted by Phoracantha semipunctata may be seen as a positive factor in some regions, as Eucalyptus trees that are introduced are seen as invasive plant species imposing harm on the natural environment.
Phoracantha semipunctata are typically dark brown & beige in colour and are approximately similar in size measuring at around 2.3cm long. They are primarily active during the more temperate initial dusk hours, and are found in populations within host trees, which are predominantly male-oriented. These host trees are determined according to the suitability of adult mating and oviposition, and the viability of larvae development.
Taxonomy
Phoracantha semipunctata was initially observed in the late 1980s in Setubal Portugal. The beetle is classified as a species within the Phoracantha genus, situated within the Phoracanthini tribe of beetles under the Cerambycinae subfamily, which it shares with 11 other genera including Coptocercus, Allotisis, Thoris, Epithora, Skeletodes, Atesta, Paratesta, Steata, Coleocoptus, Phytrocaria, and Semiphoracantha. Adult beetles within the Cerambycidae family are generally recognised as "longicorn" or "longhorned" beetles, due to their especially long antennae.
Description
Phoracantha semipunctata ranges from 15-23mm in length; however, females are recorded to be slightly larger than their male counterparts. Their bodies are of a darker reddish colour, and typically consists of a protruding spine at the end. Adults are primarily found during the spring and summer seasons, coming out during the evening hours, commonly feeding on pollen & nectar within host trees.
It is similar to the related P. recurva, but differs in the larger size and more extensive dark markings.
Elytra
The wings of Phoracantha semipunctata are predominantly dark brown and cream in colour, with a zigzag line dividing the cream coloured area of the elytra. Being crepuscular insects, adult flight activity is restricted to the warmer evening hours, when temperatures are above 15 degrees celsius. Adults fly, seeking mates and females scout for any potential areas in which they can oviposit. Flight activity is determined by host tree odours. This influences adults to fly in a more upwind motion and land on specific areas of the tree, and also acts as a factor upon when they fly-off. When adults acquire a distinct sense for the odour, they fly in a manner where they move in a compressed non-linear motion. When searching for a host tree, adults utilise a specific flight mechanic that consists of an odour oriented optomotor and autonomous contrary zig-zag movements.