Natural enemies implicated in the regulation of an invasive pest: a life table analysis of the population dynamics of the emerald ash borer

The emerald ash borer Agrilus planipennisFairmaire is a serious invasive forest pest of ash (Fraxinus) trees in North America. Life tables were constructed for both experimentally established cohorts and wild populations of A. planipennis on healthy host trees from 2008 to 2011 in six forests in central Michigan. Life table analysis showed that the net population growth rates (R-0) for the experimental cohorts (16.02.9) and associated wild A. planipennis (19.4 +/- 1.9) were the highest for the first study period (2008-2009) at three Ingham Co. sites but decreased to 4.7 +/- 0.9 and 4.6 +/- 0.4, respectively, for the second (2009-2010) study period at the same sites. By contrast, R-0 values of both experimental cohorts (5.7 +/- 2.2) and associated wild A. planipennis populations (11.3 +/- 2.5) were intermediate in the third (2010-2011) study period at different sites in the Gratiot and Shiawassee Cos. The sudden decrease in R-0 of both experimental and wild A. planipennis cohorts in the Ingham Co. sites corresponded with increases in parasitism by hymenopteran parasitoids Atanycolus spp. (native) and Tetrastichus planipennisiYang (introduced), as well as an increase in woodpecker predation, indicating the role of these natural enemies in regulation of the pest's population dynamics.