Spathius agrili
Encyclopedia
Spathius agrili is a parasitic non-stinging wasp of family Braconidae
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 destroyed tens of millions of ash trees in its introduced range in North America
. As part of the campaign against the emerald ash borer (EAB), American scientists in conjunction with the Chinese Academy of Forestry searched since 2003 for its natural enemies in the wild leading to the discovery of several parasitoid wasps, including Spathius agrili which was discovered in Tianjin
, China
where it is a prevalent gregarious ectoparasitoid of EAB larvae in stands of Fraxinus velutina
, an ash species native to Mexico
and southwestern U.S.A., and one ash tree endemic to the region, Fraxinus mandshurica and has been recorded to attack and kill up to 90 percent of EAB larvae.
The life cycle of the wasp 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. S. agrili completes three generations per year (Yang et al. 2005). The female wasps can oviposit through the tree bark, paralyzing the larva and laying a clutch of eggs on the integument. When the larvae mature, they spin a cocoon
and pupate within the host gallery. Spathuis overwinter as pupae inside cocoons under the bark of ash trees and emerge as adults in the summer. No-choice laboratory assays of larval wood-boring insects from China and North America showed some overlap in the physiological host.
, a solitary, parthenogenic egg parasitoid, has been introduced and released into the United States of America as a possible biological control of the EAB. However of the three, Tetrastichus planipennisi has showed best results in affecting EAB and establishing surviving populations.
Research on the viability of as an effective biocontrol agent is ongoing in the US. Laboratory methods have been developed for continuous rearing of this and other species of EAB parasitoid wasps. Extensive studies on the specificity of these parasitoids on native beetles and other insects has been carried out. No-choice laboratory assays of larval wood-boring insects from China and North America showed some overlap in the physiological host range of S. agrili, although successful parasitism was significantly lower in non-hosts than in EAB. S. agrili also did not attack any borers in genera other than Agrilus. S. agrili was only attracted to select species of Fraxinus and to Salix babylonica. Since in nature, if parasitoids are not attracted to the host tree they will be unlikely to encounter and parasitize the non-target larvae, and considering the results from no-choice and olfactometer tests, the lack of S. agrili reared from other Agrilus spp, the wasp has been accepted for controlled releases in specific study sites for further research.
Braconidae
Braconidae is a family of parasitoid wasps and one of the richest families of insects. Between 50,000 and 150,000 species exist worldwide. The species are grouped into about 45 subfamilies and 1,000 genera, some important ones being: Ademon, Aphanta, Asobara, Bracon hebetor, Cenocoelius, Chaenusa,...
which is native to North Asia
North Asia
North Asia or Northern Asia is a subregion of Asia, consisting of the Asian portion of Russia.The Phillips Illustrated Atlas of the World 1988 defines it as being most of the former USSR, the part that is to the east of the Ural Mountains...
. It is a parasitoid of the emerald ash borer
Emerald ash borer
The emerald ash borer is a green beetle native to Asia.In North America the borer is an invasive species, highly destructive to ash trees in its introduced range. The potential damage of this insect rivals that of Chestnut blight and Dutch Elm Disease...
(Agrilus planipennis Fairmaire, family Buprestidae), an invasive species
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
which has destroyed tens of millions of ash trees in its introduced range in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. As part of the campaign against the emerald ash borer (EAB), American scientists in conjunction with the Chinese Academy of Forestry searched since 2003 for its natural enemies in the wild leading to the discovery of several parasitoid wasps, including Spathius agrili which was discovered in Tianjin
Tianjin
' is a metropolis in northern China and one of the five national central cities of the People's Republic of China. It is governed as a direct-controlled municipality, one of four such designations, and is, thus, under direct administration of the central government...
, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
where it is a prevalent gregarious ectoparasitoid of EAB larvae in stands of Fraxinus velutina
Fraxinus velutina
Fraxinus velutina 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 to Coahuila and Nuevo León.-Description:Fraxinus velutina is a small deciduous tree growing to 10 m tall,...
, an ash species native to Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
and southwestern U.S.A., and one ash tree endemic to the region, Fraxinus mandshurica and has been recorded to attack and kill up to 90 percent of EAB larvae.
The life cycle of the wasp 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. S. agrili completes three generations per year (Yang et al. 2005). The female wasps can oviposit through the tree bark, paralyzing the larva and laying a clutch of eggs on the integument. When the larvae mature, they spin a cocoon
Cocoon
Cocoon may refer to:*Cocoon , a pupal casing made by moth caterpillars and other insect larvae*Apache Cocoon, web development software*Cocoon , a 1985 science fiction film**Cocoon: The Return, 1988 sequel to Cocoon...
and pupate within the host gallery. Spathuis overwinter as pupae inside cocoons under the bark of ash trees and emerge as adults in the summer. No-choice laboratory assays of larval wood-boring insects from China and North America showed some overlap in the physiological host.
Biological control
Spathius agrili, a gregarious larval ectoparasitoid, Tetrastichus planipennisi, a gregarious larval endoparasitoid, and Oobius agriliOobius 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 , an invasive species which has destroyed tens of millions of ash trees in its introduced range in North America...
, a solitary, parthenogenic egg parasitoid, has been introduced and released into the United States of America as a possible biological control of the EAB. However of the three, Tetrastichus planipennisi has showed best results in affecting EAB and establishing surviving populations.
Research on the viability of as an effective biocontrol agent is ongoing in the US. Laboratory methods have been developed for continuous rearing of this and other species of EAB parasitoid wasps. Extensive studies on the specificity of these parasitoids on native beetles and other insects has been carried out. No-choice laboratory assays of larval wood-boring insects from China and North America showed some overlap in the physiological host range of S. agrili, although successful parasitism was significantly lower in non-hosts than in EAB. S. agrili also did not attack any borers in genera other than Agrilus. S. agrili was only attracted to select species of Fraxinus and to Salix babylonica. Since in nature, if parasitoids are not attracted to the host tree they will be unlikely to encounter and parasitize the non-target larvae, and considering the results from no-choice and olfactometer tests, the lack of S. agrili reared from other Agrilus spp, the wasp has been accepted for controlled releases in specific study sites for further research.