Biological control against Agrilus planipennis in Canada and the USA
In North America, Agrilus planipennis (Coleoptera: Buprestidae - EPPO A1 List) was first found in southeastern Michigan and adjacent areas of Canada in 2002. It is suspected that it was introduced in the early 1990s via wood packaging material from Asia. As of March 2016, A. planipennis occurs in 25 US states (Arkansas, Colorado, Connecticut, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland, Massachusetts, Michigan, Minnesota, Missouri, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia, and Wisconsin) and 2 Canadian provinces (Ontario and Québec). In the USA, it is estimated that federal and state resource managers are spending 29.5 million USD per year to manage A. planipennis populations. Considering the severity of damage to ash trees (Fraxinus spp.) eradication measures were implemented soon after the first detection of A. planipennis. However, due to the rapid spread of the pest and general lack of effective detection and control methods, strategies shifted from eradication to containment programmes. In particular, the current strategies are focusing on the use of biocontrol agents, and several hymenopteran parasitoids collected from China, the Republic of Korea and Russia have been identified as potential candidates. Four species (Oobius agrili, Spathius agrili, Spathius galinae, and Tetrastichus planipennisi) have been approved for release as biocontrol agents in the USA, and others are under consideration. During recent studies a new species, Oobius primorskyensis n. sp., has been described. This egg parasitoid has been collected from A. planipennis near Vladivostok in Russia.
- Oobius agrili (Hymenoptera: Encyrtidae) is an egg parasitoid of A. planipennis. In China, it can parasitize up to 60% of the pest eggs during summer. Each female can parasitize up to 80 eggs during its lifetime.
- Spathius agrili (Hymenoptera: Braconidae). It has been observed that this species could parasitize up to 90% of A. planipennis larvae in ash trees in Tianjin (China). Females parasitize larvae by drilling through the bark and laying an average of 8 eggs on the host larva.
- Spathius galinae (Hymenoptera: Braconidae) has a similar biology to S. agrili but has been collected from Russia and the Republic of Korea. In Russia, S. galinae can parasitize up to 60 % of the larvae inside ash trees.
- Tetrastichus planipennisi (Hymenoptera: Eulophidae) is a larval parasitoid. In some areas of China, it can parasitize up to 50% of the pest larvae. Its life cycle is similar to that of Spathius species but females lay eggs inside the larvae.
Since 2009, parasitoids are being reared in a dedicated facility in Michigan (US). As of February 2016, more than 3 million parasitoids have been reared and released in 22 US states and 2 Canadian provinces. Tetrastichus planipennisi and Oobius agrili are establishing in multiple states. These two species are dispersing from the release sites and percentages of parasitism continue to increase. Spathius agrili has not been able to establish in northern states. For the moment, Spathius galinae was only released in small numbers in 2015 but more releases are taking place in 2016.
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USDA-Forest Service. Emerald ash borer. http://www.nrs.fs.fed.us/disturbance/invasive_species/eab/control_management/biological_control/
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