''Leptocybe invasa'', the blue gum chalcid wasp or eucalyptus gall wasp, is a

chalcid wasp Chalcid wasps (, , for their metallic colour) are insects within the superfamily Chalcidoidea, part of the order Hymenoptera. The superfamily contains some 22,500 known species, and an estimated total diversity of more than 500,000 species, m ...

which is the only species in the

monotypic genus In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...

''Leptocybe'' in the subfamily

Tetrastichinae Tetrastichinae is a subfamily of the chalcid wasp family Eulophidae. It is one of the largest subfamilies of the Eulophidae containing over 100 genera and nearly 3,000 species. The species of the family Tetrastichinae are found in almost any type ...

, of the family

Eulophidae The Eulophidae is a large family of hymenopteran insects, with over 4,300 described species in some 300 genera. The family includes the genus '' Elasmus'', which used to be treated as a separate family, "Elasmidae", and is now treated as a subfa ...

. It is a

gall wasp Gall wasps, also traditionally called gallflies, are hymenopterans of the family Cynipidae in the wasp superfamily Cynipoidea. Their common name comes from the galls they induce on plants for larval development. About 1,300 species of this gene ...

which causes the formation of

gall Galls (from the Latin , 'oak-apple') or ''cecidia'' (from the Greek , anything gushing out) are a kind of swelling growth on the external tissues of plants. Plant galls are abnormal outgrowths of plant tissues, similar to benign tumors or war ...

s on a number of species of ''

Eucalyptus ''Eucalyptus'' () is a genus of more than 700 species of flowering plants in the family Myrtaceae. Most species of ''Eucalyptus'' are trees, often Mallee (habit), mallees, and a few are shrubs. Along with several other genera in the tribe Eucalyp ...

'', it was described in 2004 after galls were found in river red gums (''Eucalyptus camaldulensis'') in the Mediterranean and Middle East and has since been found to be a widespread species where its host trees are planted. It is indigenous to Australia.

Description

This tiny wasp is just over one millimeter in length. Its body is brown with a slight blue to green

iridescence Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear gradually to change colour as the angle of view or the angle of illumination changes. Iridescence is caused by wave interference of light in microstru ...

. Parts of the legs are yellowish in color.

Distribution

''Leptocybe invasa'' is native to

Queensland Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...

, Australia where its exact distribution has yet to be determined. It has now been found as an

invasive species An invasive species is an introduced species that harms its new environment. Invasive species adversely affect habitats and bioregions, causing ecological, environmental, and/or economic damage. The term can also be used for native spec ...

in eucalypts in northern, eastern and southern Africa, Asia, the Pacific Region, Europe as far north as the United Kingdom, southern Asia, southern South America, the Middle East, Mexico and the United States. It appears to be spreading.''Leptocybe invasa''.
FAO Forest Pest Species Profiles. August 2012.Blue Gum Chalcid.
Pest Fact Sheet. Asia-Pacific Forest Invasive Species Network.

Discovery

''L. invasa'' was discovered in 2000 when river red gums in the Middle East and Mediterranean began developing disfiguring

s. The damage became severe enough to cause crop losses in tree plantations. Galls were collected and a previously undescribed species of chalcid wasp emerged. In 2004 it was described to science as ''Leptocybe invasa''.

Biology

The adult female injects a neat line of minute eggs in the epidermis of new leaf buds on eucalyptus trees. The leaf tissue may exude a whitish sap, which covers the oviposition site. Heavy wasp infestations can kill new buds on the trees. If the bud survives it develops a layer of corky tissue within one to two weeks of oviposition. This corky scar widens and becomes glossy in texture. It turns from green to pinkish to dark pink or red in color. It loses its glossy texture and turns dull brown or reddish. The chalcid wasp larva develops inside the gall and when it emerges as an adult insect the gall is spherical and up to 2.7 millimeters wide. During an infestation there are usually 3 to 6 galls per leaf, but up to 65 have been observed on a single leaf. The adult wasps emerge from the galls after growing inside for 3–4 months. In temperate areas there may be 2-3 generations of adults in a year but in the tropics there can be as many as 6 generations. The females can reproduce asexually by thelytokous reproduction and live for up to 7 days, males are rare and the asexual reproduction allows ''L. invasa'' to rapidly increase its population size. Several eucalyptus species are susceptible to the wasp. Host species include bangalay (''Eucalyptus botryoides''),

apple box Apple boxes are wooden boxes or crates of varying sizes with holes on each end used mainly in film production. These boxes are specialized pieces of equipment belonging to the grip department, and should not be confused with simple crates, ot ...

(''E. bridgesiana''),

Tasmanian blue gum ''Eucalyptus globulus'' subsp. ''globulus'', commonly known as the Tasmanian blue gum, southern blue gum, or blue gum, is a subspecies of tree that is Endemism, endemic to southeastern Australia. It has mostly smooth bark with some persistent sl ...

(''E. globulus''), cider gum (''E. gunnii''), flooded gum (''E. grandis''), swamp mahogany (''E. robusta''),

Sydney blue gum ''Eucalyptus saligna'', commonly known as the Sydney blue gum or blue gum, is a species of medium-sized to tall tree that is endemic to eastern Australia. It has rough, flaky bark near the base of the trunk, smooth bark above, lance-shaped to c ...

(''E. saligna''),

forest red gum ''Eucalyptus tereticornis'', commonly known as forest red gum, blue gum or red irongum, is a species of tree that is native to eastern Australia and southern New Guinea. It has smooth bark, lance-shaped to curved adult leaves, flower buds in grou ...

(''E. tereticornis''), and

manna gum ''Eucalyptus viminalis'', commonly known as the manna gum, white gum or ribbon gum, is a species of small to very tall tree that is endemic to south-eastern Australia. It has smooth bark, sometimes with rough bark near the base, lance-shaped to c ...

(''E. viminalis'').

Control

Possible

biological Biology is the scientific study of life and living organisms. It is a broad natural science that encompasses a wide range of fields and unifying principles that explain the structure, function, growth, origin, evolution, and distribution of ...

agents for ''L. invasa'' have been actively searched for and numerous hymenopteran parasitoids of ''L. invasa'' were identified; in one study in

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

these were ''

Quadrastichus mendeli ''Quadrastichus'' is a genus of hymenopteran insects of the family Eulophidae. Species include ''Quadrastichus erythrinae ''Quadrastichus erythrinae'' Kim, 2004, (''quadra''=four, ''stichus''=line, ''erythrinae''=of erythrina) is a small pa ...

'', '' Aprostocetus causalis'' and ''

Megastigmus viggianii ''Megastigmus'' is a genus of minute wasps. There are more than 134 described species, more than half of which undergo larval development within the seeds of trees and shrubs. List of species * '' Megastigmus acaciae'' Noble, 1939 * '' Megast ...

'', and in another study in

Israel Israel, officially the State of Israel, is a country in West Asia. It Borders of Israel, shares borders with Lebanon to the north, Syria to the north-east, Jordan to the east, Egypt to the south-west, and the Mediterranean Sea to the west. Isr ...

these were '' Megastigmus zvimendeli'', '' Megastigmus lawsoni'', '' Selitrichodes kryceri'' and ''

''.Zvi Mendel, Alex Protasov, John La Salle, Daniel Blumberg, David Brand, Manuela Branco (2017) Classical biological control of two Eucalyptus gall wasps; main outcome and conclusions. Biological Control 105: 66-78. https://doi.org/10.1016/j.biocontrol.2016.11.010 ''

'' has a short developmental time and has proven to be an especially effective control agent in the Mediterranean Basin. '' Selitrichodes neseri'' is another eulophid ectoparasitoid which is species specific to ''L. invasa'' and was discovered in its native Australian range in 2014 and show potential as a biological control agent on ''L. invasa''.

References

{{Taxonbar, from=Q13393715 Eulophidae Insects described in 2004 Agricultural pest insects Hymenoptera of Australia