Blue gum chalcid

Blue gum chalcid
Leptocybe invasa
Leaf gall forming

Leptocybe invasa is a gall-forming wasp of various Eucalyptus species. Gall-formation occurs on the leaves, petioles and stems of the young growing plant part.  Area of gall-formation (i.e. leaves, petiole, stem) on the host is dependent on the host species. Large numbers of the wasp result in a high frequency of oviposition which may results in stunted growth or even tree death. Seedlings, coppice growth and young developing leaves are at highest risk (Mendel et al. 2004).

The wasp is 1.1 – 1.4 mm in size with a brown head and body which has a blue to green metallic shine. The head is weak with a distinct groove between the head and thorax. The fore coxa are yellow and the middle and hind coxae the same colour as the insect body. The wings are translucent with a “smoky” patch  (Mendel et al. 2004).

There are two distinct genetic lineages present in South Africa (Dittrich-Schröder et al. 2018), but they are morphologically indistinguishable.

Leptocybe invasa has a thelytokous reproductive system, where all offspring are female and are produced parthenogenetically. Male specimens are absent or very rare. Oviposition occurrs on young plant tissue of the stem, petiole and leaves as early as 1-2 weeks after bud break out. Eggs are laid in a line on the young plant tissue and are often visible as minute black scarring or dots, especially along the leaf midrib. Average developmental time from oviposition to wasp emergence is approximately 4.5 months.

Wasps are most active in the early morning and late afternoon and may survive to 6 days if provided with sources of honey and water. Oviposition occurs in the summer months with a single female being able to lay up 250 eggs.

As there are differences in susceptibility between Eucalyptus varieties, selection of more resistant planting material is a possible management strategy. In addition, a biological control agent, Selitrichodes neseri, was released in South Africa in 2012 (Dittrich-Schroder et al. 2014) and is now widely established throughout the country. Other parasitic wasps have also been found associated with galls of Leptocybe invasa, adding to the suppression of this pest. Host selection and biological control should preferably be used in combination.

2007 (Dittrich-Schröder et al. 2012)
All provinces
Various eucalypt species and varities, but with differences in susceptibility.
Australia

Gallery

Galls on petioles
Adult female
Oviposition marks/scars along midrib of leaf
Galls on midrib of leaves
Adult male
Larvae inside cavities within gall

Dittrich-Schröder G, Wingfield MJ, Hurley BP, Slippers B. 2012. Diversity in Eucalyptus susceptibility to the gall-forming wasp Leptocybe invasa. Agricultural and Forest Entomology 14:419-427

Dittrich-Schröder G, Harney M, Neser S, Joffe T, Bush S, Hurley BP, Wingfield MJ, Slippers B. 2014. Biology and host preference of Selitrichodes neseri: A potential biological control agent of the Eucalyptus gall wasp, Leptocybe invasa. Biological Control 78:33-41

Dittrich-Schröder G, Hoareau TB, Hurley BP et al. 2018. Population genetic analyses of complex global insect invasions in managed landscapes: a Leptocybe invasa (Hymenoptera) case study. Biol ogical Invasions 20: 2395–2420.

Mendel Z, Protasov A, Fisher N, La Salle J. 2004. Taxonomy and biology of Leptocybe invasa gen. & sp. n. (Hymenoptera: Eulophidae), an invasive gall inducer on Eucalyptus. Australian Journal of Entomology 43:101-113