Location: Beneficial Insects Introduction ResearchTitle: Natural enemies implicated in the regulation of an invasive pest: a life table analysis of the population dynamics of the emerald ash Borer) Author
Submitted to: Agricultural and Forest Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/31/2014
Publication Date: 5/27/2014
Publication URL: DOI:10.1111/afe.12070
Citation: Duan, J.J., Abell, K., Bauer, L., Gould, J., Van-Driesch, R. 2014. Natural enemies implicated in the regulation of an invasive pest: a life table analysis of the population dynamics of the emerald ash borer. Agricultural and Forest Entomology. DOI:10.1111/afe.12070. Interpretive Summary: The emerald ash borer (EAB), Agrilus planipennis Fairmaire, is a serious invasive forest pest that has killed tens of millions of ash (Fraxinus) trees in the United States and Canada. Understanding EAB population changes and the role of various factors in suppressing their population growth is critical to the development of sound pest management strategies. By caging EAB adults on trunks of healthy ash trees, we studied the impacts of different factors on the population changes of this pest from 2008 to 2011 in six forests in central Michigan. Findings from our study showed that levels of the beetle mortality varied significantly among different insect life stages. Throughout the study, later stages had higher levels of mortality than earlier stages. Host tree resistance and/or disease were the dominant mortality factor associated with the earlier stages. The primary mortality factor for the last stage appeared to be parasitism by native parasitic wasps (Atanycolus spp.) and an introduced, exotic parasitic wasp (Tetrastichus planipennisi). Predation by woodpeckers was the dominant mortality factor for the mature larvae that had already made chambers in the sap wood for overwintering. These finding suggests that factors such as parasitoids and woodpeckers played a critical role in regulating the EAB population dynamics in Michigan.
Technical Abstract: The emerald ash borer (EAB), Agrilus planipennis Fairmaire, is a serious invasive forest pest that has killed tens of millions of ash (Fraxinus) trees in the United States and Canada. By caging EAB adults on trunks of healthy ash trees, we established three generations of experimental cohorts from 2008 to 2011 in six forests in central Michigan and subsequently measured the apparent mortality of immature stages of those cohorts, along with measurements of abundance of naturally occurring (wild) populations. Based on separate estimates of adult fecundity and egg mortality, we then constructed life tables for both experimental and wild EAB cohorts and compared their net population growth rates (R0) for each generation across different study sites. Results showed that R0 (+/- SE) for the experimental cohorts (16.0 +/- 2.9) and associated wild EAB stages (19.4 +/- 1.9) were the highest for the first (2008-2009) generation at three Ingham Co. sites, but decreased to 4.7 +/- 0.9 and 4.6 +/- 0.4, respectively, for the second (2009-2010) generation at the same sites. This sudden decrease in R0 of both experimental and wild EAB cohorts in those sites corresponded with increases in parasitism by native parasitoids (Atanycolus spp.) (Hymen.: Braconidae) and the introduced biocontrol agent Tetrastichus planipennisi Yang (Hymen.: Eulophidae). In contrast, R0 values of both experimental cohorts (5.7 +/- 2.2) and associated wild EAB populations (11.3 +/- 2.5) were intermediate in the third (2010 – 2011) generation at different sites in the Gratiot and Shiawassee Cos. There was no significant difference in R0 values between the experimental cohorts and wild EAB populations for the first and second generations. However, R0 of the experimental cohorts was significantly lower than that of associated wild EAB population for the 3rd generation. Relevance of our findings to EAB population dynamics in the invasion process is discussed.