Measuring the Impact of Biotic Factors on Populations of Immature Emerald Ash Borers (Coleoptera: Buprestidae)

Abstract

Cohorts of emerald ash borer larvae, Agrilus planipennis Fairmaire, were experimentally established in July of 2008 on healthy green ash (Fraxinus pennsylvanica) trees in two wooded plots at each of three sites near Lansing, MI, by caging gravid emerald ash borer females or placing laboratory-reared eggs on trunks (0.5-2 m above the ground) of selected trees. One plot at each site was randomly chosen for release of two introduced larval parasitoids, Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae) and Spathius agrili Yang (Hymenoptera: Braconidae), whereas the other served as the control. Stage-specific mortality factors and rates were measured for all experimentally established cohorts and for associated wild (i.e., naturally occurring) emerald ash borer immature stages via destructive sampling of 2.5 m (above the ground) trunk sections of cohort-bearing trees in the spring and fall of 2009. Host tree defense was the most important mortality factor, causing 32.0 to 41.1% mortality in the experimental cohorts and 17.5 to 21.5% in wild emerald ash borer stages by spring 2009, and 16.1 to 29% for the remaining experimental cohorts, and 9.9 to 11.8% for wild immature emerald ash borer stages by fall 2009. Woodpecker predation was the second most important factor, inflicting no mortality in the experimental cohorts but causing 5.0 to 5.6% mortality to associated wild emerald ash borer stages by spring 2009 and 9.2 to 12.8% and 3.2 to 17.7%, respectively, for experimental cohorts and wild emerald ash borer stages by fall 2009. Mortality from disease in both the experimental and wild cohorts was low (<3%) in both the spring and fall sample periods. In the fall 2009 samples, ≈ 1.5% of experimental cohorts and 0.8% of the wild emerald ash borer stages were parasitized by T. planipennisi. While there were no significant differences in mortality rates because of parasitism between parasitoid-release and control plots, T. planipennisi was detected in each of the three release sites by the end of the study but was not detected in the experimental cohorts or associated wild larvae in any of the three control plots.

Factors Affecting the Flight Capacity of <I>Tetrastichus planipennisi</I> (Hymenoptera: Eulophidae), a Classical Biological Control Agent of <I>Agrilus planipennis</I> (Coleoptera: Buprestidae)

“…In Michigan, emerald ash borer development rates vary from 1 to 2 yr depending on tree species, tree health, environmental conditions, and time of oviposition (Cappaert et al 2005;Duan et al 2010;Siegert et al 2010;Tluczek et al 2011;Herms & McCullough 2014). Therefore, emerging parasitoids encounter a great deal of variation in the presence and abundance of suitable hosts throughout the year.…”

Population responses of hymenopteran parasitoids to the emerald ash borer (Coleoptera: Buprestidae) in recently invaded areas in north central United States

“…EAB populations in the northern United States (e.g., Michigan and Pennsylvania) may require two years to complete development, especially in newly infested, healthy ash trees (Cappaert et al 2005;Siegert et al 2007;Duan et al 2010). Similar developmental plasticity is known for Agrilus anxius Gory, a native buprestid that feeds on birch trees (Barter 1957).…”

“…(Eupelmidae) (Bauer et al 2004Lyons 2008;Cappaert and McCullough 2009;Duan et al 2009;Kula et al 2010). The highest known level of mortality, however, is caused by woodpeckers, which attack the larger, immature stages of EAB in North America (Cappaert et al 2005;Lindell et al 2008;Duan et al 2010). Host-tree resistance and pathogenic microorganisms also influence the survival and reproduction of EAB in both North America (Bauer et al 2004;Rebek et al 2008;Duan et al 2010) and Asia (Liu and Bauer 2006;Liu et al 2007;Duan et al 2011).…”

“…The highest known level of mortality, however, is caused by woodpeckers, which attack the larger, immature stages of EAB in North America (Cappaert et al 2005;Lindell et al 2008;Duan et al 2010). Host-tree resistance and pathogenic microorganisms also influence the survival and reproduction of EAB in both North America (Bauer et al 2004;Rebek et al 2008;Duan et al 2010) and Asia (Liu and Bauer 2006;Liu et al 2007;Duan et al 2011). Although the combined rate of attack by these various mortality agents is inadequate to suppress EAB spread and ash mortality in North America, their potential role in regulating population dynamics may increase over time and needs to be investigated for the purpose of managing this invasive pest.…”

Parasitoid Guilds ofAgrilusWoodborers (Coleoptera: Buprestidae): Their Diversity and Potential for Use in Biological Control

“…These classical biological control efforts for EAB have led to the discovery and introduction of several egg and larval parasitoids that have the potential to establish and suppress the pests' populations in the newly introduced regions [19][20][21]27]. Similar programs for GSOB commenced in 2010 and are too immature to reach tentative conclusions about natural enemy diversity and impacts.…”