Perilampella acaciaediscoloris: An Australian Gall Wasp

The small but incredibly diverse chalcidoid wasps are mostly known as parasitoids, their larvae attacking the eggs and young of others insects. Some, however, have chosen the vegetarian option, inserting their eggs into plant rather than animal tissue. As the larva develops, it induces the host plant to develop an often bizarre-looking growth around it that provides both shelter and food; this growth is known as a gall.

Antenna, forewing venation and dorsum of Perilampella acaciaediscoloris, from Bouček (1988).

Perilampella acaciaediscoloris is an gall-forming wasp that was first described by Froggatt in 1892 from galls that he collected on the wattle Acacia discolor, a species now regarded as a synonym of the sunshine wattle A. terminalis of south-eastern Australia. Froggatt placed his species in the genus Cynips (which is not part of the Chalcidoidea but belongs to a different micro-wasp superfamily, the Cynipoidea) but it is now placed in the chalcid subfamily Ormocerinae in the (polyphyletic) Pteromalidae. Ormocerinae are fairly generalised 'pteromalids' that are non-metallic in colour and often finely sculpted. So far as is known, ormocerines are all associated with galls in one way or another, either as gall-causers themselves or as inquilines (species that lay their eggs in the galls caused by other insects). Another ormocerine species, Trichilogaster acaciaelongifoliae, has been introduced from Australia to South Africa to help control the Sydney golden wattle Acacia longifolia.

The related ormocerine Trichilogaster acaciaelongifoliae, copyright Simon van Noort. Perilampella acaciaediscoloris most obviously differs from this species in its hairier and darker wings, and more shiny mesosoma.

The genus Perilampella differs from other ormocerines in being particularly shiny, with little clear setation. Bouček (1988) listed four Australian species in the genus, noting that P. acaciaediscoloris could be recognised by its very dark, long wings and shiny orange-yellow mesosoma. Froggatt (1892) described the galls of P. acaciaediscoloris as formed at the inception of a leaf bud or new shoot. Sometimes, they would be little more than swellings at the base of the shoot. More often, they would be oval with three irregular horns formed from aborted leaf buds. Sometimes, P. acaciaediscoloris galls would be the target of inquilines of their own that caused the gall to degrade to a shapeless mass.

REFERENCES

Bouček, Z. 1988. Australian Chalcidoidea (Hymenoptera): A biosystematic revision of genera of fourteen families, with a reclassification of species. CAB International.

Froggatt, W. W. 1892. Notes on Australian Cynipidae, with descriptions of several new species. Proceedings of the Linnean Society of New South Wales, second series 7: 152–156.