Establishment and Abundance of <I>Tetrastichus planipennisi</I> (Hymenoptera: Eulophidae) in Michigan: Potential for Success in Classical Biocontrol of the Invasive Emerald Ash Borer (Coleoptera: Buprestidae)

Abstract

Tetrastichus planipennisi Yang is a gregarious larval endoparasitoid native to China and has been introduced to the United States since 2007 for classical biological control of the invasive emerald ash borer, Agrilus planipennis Fairmaire, an exotic beetle responsible for widespread ash mortality. Between 2007-2010, T. planipennisi adults (3,311-4,597 females and approximately 1,500 males per site) were released into each of six forest sites in three counties (Ingham, Gratiot, and Shiawassee) of southern Michigan. By the fall of 2012, the proportion of sampled trees with one or more broods of T. planipennisi increased to 92 and 83% in the parasitoid-release and control plots, respectively, from 33 and 4% in the first year after parasitoid releases (2009 fall for Ingham county sites and 2010 for other sites). Similarly, the mean number of T. planipennisi broods observed from sampled trees increased from less than one brood per tree in the first year after parasitoid releases to 2.46 (at control plots) to 3.08 (at release plots) broods by the fall of 2012. The rates of emerald ash borer larval parasitism by T. planipennisi also increased from 1.2% in the first year after parasitoid releases to 21.2% in the parasitoid-release plots, and from 0.2 to 12.8% for the control plots by the fall of 2012. These results demonstrate that T. planipennisi is established in southern Michigan and that its populations are increasing and expanding. This suggests that T. planipennisi will likely play a critical role in suppressing emerald ash borer populations in Michigan.

Buying Time: Preliminary Assessment of Biocontrol in the Recovery of Native Forest Vegetation in the Aftermath of the Invasive Emerald Ash Borer

“…First, parasitoid release information (number of released T. planipennisi, as this was the most successful parasitoid establishing and spreading [37,62]) was used to analyze ash sapling density, then invasive and weedy species density was analyzed as a function of the estimated ash sapling densities, and we finished by using estimates of invasive and weedy species densities to analyze the native tree seedling data (Figure 1b). This multilevel approach allowed sharing of information across the data sets [65], potentially better informing the dynamics taking place in these plots.…”

“…At the release sites, the relative release proportions for O. agrili, T. planipennisi, and S. agrili were 19%, 68% and 13% respectively. Both O. agrili and T. planipennisi were confirmed established at one of the seven parasitoid-release plots, whereas establishment of T. planipennisi was confirmed at two other release plots; establishment of S. agrili has not been confirmed [61][62][63].…”

Progress and Challenges of Protecting North American Ash Trees from the Emerald Ash Borer Using Biological Control

“…The long-term study consisted of six forested sites in southern Michigan, each comprised of a release and non-release control plot, which were established between 2007 and 2010. At each release plot, small numbers of adult O. agrili, S. agrili, and T. planipennisi were released, and in subsequent years, infested ash trees are being sampled to estimate EAB egg and larval parasitism, and other causes of larval mortality [81,82].…”

“…Using this approach, average larval parasitism by T. planipennisi was~1 to 6% from 2008-2011 and increased to~30% by 2014 in both the release and control plots [81,95,96]. As more recovery work is done in this and other regions, researchers are finding a rapid spread of T. planipennisi across EAB-infested sites (Figure 2b).…”

“…In 2007, after USDA APHIS issued permits for the environmental release of O. agrili, S. agrili, and T. planipennisi in Michigan, small numbers (a few hundred per species) were laboratory-reared and released at a few sites [18,81,82]. In subsequent years, larger numbers of parasitoids were released (tens of thousands) in additional states after USDA APHIS' EAB biocontrol mass-rearing facility in Brighton, Michigan became operational in 2010 [19,20,83].…”