Oemona hirta, the lemon tree borer, also known as the whistling beetle or the singing beetle, is a longhorn beetle endemic to New Zealand. Its larvae are generalist feeders, boring into the wood of a wide variety of trees, native and introduced. When citrus orchards were first established in New Zealand, this beetle started inflicting serious damage, and so gained the name "lemon tree borer". Four species within the genus Oemona have been identified, suggesting that more species could be found. When disturbed by predators or humans, the adult beetle stridulates creating a "rasp" or "squeak" sound by rubbing its thorax and head together against an area of thin ridges. Māori would eat a liquid called "pia manuka", which was produced by manuka trees when its wood was damaged by the larvae. When Captain Cook first arrived in NZ, his naturalists, Banks and Solander, collected a lemon tree borer in their first collection between 1769 and 1771. This oldest collected specimen can be found in the British Museum. A few years after the first collection, the species would be first described by the Danish naturalist Fabricius in 1775.
Description
Adults: The lemon tree borer is a plain looking, medium to large sized beetle, reaching long. It has a slender body with elongated antennae. Antennae are usually the same length as or longer than the body, and able to sit in front of, or curve backwards against the body. Adults can vary from red-brown to almost black in colour, with patches of pale yellow hairs on the head and scutellum, which is a small spot on their back where the thorax joins the elytra (hard wing cases). Females are larger and heavier than males, but have proportionally shorter antennae, but the sex can only be reliably determined by looking at the genitalia using a microscope. A distinctive feature of O. hirta is the transverse wrinkling on the dorsal surface of the pronotum; this is especially distinctive on males.
Eggs: White and large (2.0-2.2mm) with a fine waxy surface pattern, they are laid singly in leaf or stem junctions, pruning and cicada scars, damaged bark or dead twigs on the outer edge of trees.
Larvae: Their skin is white to pale cream with orange to brown gut contents, growing 25-40mm long. Body is cylindrical with each thoracic and abdominal segment having a swollen transverse ridge; an enlarged head holds gouge-like mandibles (biting jaws) which are large but short and dark brown to black. Many minute rigid brown hairs line the lateral margins, especially towards the head. When disturbed, larvae are able to move surprisingly fast due to dorsal and ventral muscle ridges gripping its surroundings.
Pupae: Approximately 20-25mm long. Pupa are a pale reddish clay colour with darker shades on the wing cases. The pupa chamber is a short length of larval tunnel with tightly packed wood shaving plugs at each end. The beetle shape is more obvious in the pupal stage, showing long antennae folded adjacent to the body and larger legs bended in. While the individual is pupating, it can twist around the chamber using small black spines on its abdomen.