''Spathius agrili'' is a parasitic non-stinging wasp of family

Braconidae The Braconidae are a family of parasitoid wasps. After the closely related Ichneumonidae, braconids make up the second-largest family in the order Hymenoptera, with about 17,000 recognized species and many thousands more undescribed. One analysis ...

which is native to

North Asia North Asia or Northern Asia, also referred to as Siberia, is the northern region of Asia, which is defined in geographical terms and is coextensive with the Asian part of Russia, and consists of three Russian regions east of the Ural Mountains: ...

. It is a parasitoid of the

emerald ash borer The emerald ash borer (''Agrilus planipennis''), also known by the acronym EAB, is a green buprestid or jewel beetle native to north-eastern Asia that feeds on ash species. Females lay eggs in bark crevices on ash trees, and larvae feed undern ...

(''Agrilus planipennis'' Fairmaire), an

invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...

which has destroyed tens of millions of

ash trees ''Fraxinus'' (), commonly called ash, is a genus of flowering plants in the olive and lilac family, Oleaceae. It contains 45–65 species of usually medium to large trees, mostly deciduous, though a number of subtropical species are evergr ...

in its introduced range in

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

. As part of the campaign against the emerald ash borer (EAB), American scientists in conjunction with the

Chinese Academy of Forestry Chinese can refer to: * Something related to China * Chinese people, people of Chinese nationality, citizenship, and/or ethnicity **''Zhonghua minzu'', the supra-ethnic concept of the Chinese nation ** List of ethnic groups in China, people of va ...

began searching in 2003 for its natural enemies in the wild, leading to the discovery of several parasitoid wasp species, including ''Spathius agrili. S. agrili'' was discovered in

Tianjin Tianjin (; ; Mandarin: ), alternately romanized as Tientsin (), is a municipality and a coastal metropolis in Northern China on the shore of the Bohai Sea. It is one of the nine national central cities in Mainland China, with a total popul ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

where it is a prevalent parasitoid of EAB larvae in stands of an introduced ash species (''

Fraxinus velutina ''Fraxinus velutina'', the velvet ash, Arizona ash or Modesto ash, is a species of '' Fraxinus'' native to southwestern North America, in the United States from southern California east to Texas, and in Mexico from northern Baja California east ...

)'', and an

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

ash species (''

Fraxinus mandshurica ''Fraxinus mandshurica'', the Manchurian ash, is a species of ''Fraxinus'' native to northeastern Asia in northern China (Gansu, Hebei, Heilongjiang, Henan, Hubei, Jilin, Liaoning, Shaanxi, Shanxi), Korea, Japan and southeastern Russia (Sakhalin ...

''). ''S. agrili'' has been recorded to attack and kill up to 90 percent of EAB larvae. This wasp is a gregarious ectoparasitoid, meaning it lays multiple eggs on the surface of its host, and the larva feed externally. The life cycle of ''S. agrili'' was found to be synchronized with that of its preferred host stages - the emergence of adult wasps took place when third and fourth-instar larvae of EAB were available. The female wasps oviposit through the tree bark, paralyze the host larva and lay a clutch of eggs on the

integument In biology, an integument is the tissue surrounding an organism's body or an organ within, such as skin, a husk, shell, germ or rind. Etymology The term is derived from ''integumentum'', which is Latin for "a covering". In a transferred, or ...

. The eggs hatch and the wasp larvae feed on the paralyzed host. When the larvae mature, they spin a cocoon and pupate within the host gallery. ''Spathuis'' overwinter as pupae within their cocoons under the bark of ash trees and emerge as adults in the summer.

Biological control

''S. agrili'', and two other species of parasitoid wasps (''Tetrastichus planipennisi'', and ''

Oobius agrili ''Oobius agrili'' is a parasitic non-stinging wasp of family Encyrtidae which is native to North Asia. It is a parasitoid of the emerald ash borer ('' Agrilus planipennis'' Fairmaire, family Buprestidae), an invasive species which has destroye ...

)'', were introduced and released into the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

biological control Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also invo ...

agents of the EAB. However, of the three, ''Tetrastichus planipennisi'' has been the most effective at parasitizing EAB and establishing self-sustaining populations. Detailed research was conducted on the wasps before they were approved for release as biocontrol agents. Laboratory methods have been developed for continuous rearing of this and other species of EAB parasitoid wasps. Extensive tests of the specificity of these parasitoids on native beetles and other insects were carried out. No-choice laboratory assays of larval wood-boring insects from China and North America showed they were capable of attacking other species of ''Agrilus'', although success of parasitism was significantly lower in species other than EAB. ''S. agrili'' was only attracted to select species of ''Fraxinus'' and to ''

Salix babylonica ''Salix babylonica'' (Babylon willow or weeping willow; ) is a species of willow native to dry areas of northern China, but cultivated for millennia elsewhere in Asia, being traded along the Silk Road to southwest Asia and Europe.Flora of China'' ...

''. In natural settings, ''S. agrili'' will be unlikely to encounter and parasitize non-target larvae as it does not search other tree species. This, in addition to other tests of host specificity, led to approval of the wasp for controlled releases in specific study sites in the United States for further research.

References

{{Taxonbar, from=Q3958372 Braconidae Biological pest control wasps Insects described in 2005