Overview
Adult orussids are rarely collected, but can sometimes be seen on sunlit tree trunks and logs. Females use their highly modified antennae and fore legs to echolocate in wood to locate suitable sites for oviposition. They oviposit into the frass-filled galleries of wood-boring cerambycid and buprestid beetles and Siricidae. The larvae develop as ectoparasitoids and later enter the host's remains to pupate.
Description
Orussids (parasitic wood wasps) are unique among the sawflies in that they are
parasitic rather than phytophagous
,
feeding externally or internally on living plant tissue,
and are considered to be an evolutionary link (i.e. sister group) to the apocritan wasps. They are characterised by having rasp-like tubercules on the vertex of the head, eyes with minute hairs, antennae inserted low on the face close to the mouth, and the ovipositor of females long and internally looped in the abdomen. Some species also have the ability to jump due to their swollen hind femora.
Most larval Symphyta differ from those of Apocrita in possessing jointed thoracic legs, although some wood-boring species are apodous. Several species, especially those that feed externally on the foliage of eucalypts, produce noxious secretions when disturbed, often accompanied by acute body contortions and a synchronised 'group response' if larvae are clustered together.
Distribution
This small family of sawflies has about 70 species worldwide and 11 described species from Australia. The only orussid in New Zealand is
Guiglia schauinslandi
, a parasitoid of the introduced
Sirex noctilio
(Siricidae).
Further information about the Orussidae can be found in Goulet 1993, Rawlings 1957, Riek 1955, Schmidt & Vilhelmsen 2002 and Vilhelmsen 2003.