2013 Annual Report
1a.Objectives (from AD-416):
To assess the establishment and impact of exotic and indigenous parasitoids on EAB populations in Maryland.
1. Establishment of at least four parasitoid release / research sites.
2. Determine the establishment and dispersal of released parasitoids at each of the release sites via general surveys.
3. Quantify EAB egg and larval survival and mortality factors via experimentally established cohorts and wild EAB populations.
1b.Approach (from AD-416):
Evaluations of egg and larval survival and mortality factors will be based on EAB life tables developed from marked cohorts of eggs and larvae on common American ash trees at a minimum of four field sites in natural forests, where some indigenous parasitoids may have become associated with EAB, and the three introduced Chinese parasitoids (Oobius agrili, Tetrastichus planipennisi, Spathius agrili) either have already been released or will be released in the first year of the study. Naturally occurring native species (if any) in each of the study sites will be treated as sequential and/or contemporary factors inflicting mortality of EAB along with the previously introduced Chinese parasitoids. If work from associated EAB projects leads to successful discovery and introduction of new species of parasitoids from Russia and/or China, these species will be introduced and then included in the evaluation studies.
In the summer of 2012 we selected 12 sites around Maryland for use in a study to construct life tables for the emerald ash borer (EAB), allowing us to examine the relative importance of different mortality factors on their population dynamics. We included three different levels of larval parasitoid treatments for our sites: two continuous years of releases, one year of releases, and control sites with no releases. We also designated sites in western Maryland to receive “low” numbers of parasitoids, while those in southern Maryland would receive “high” numbers of parasitoids, in order for us to examine the effects of parasitoid abundance on EAB. Consequently in western Maryland the two year release sites each received a total of 1900 T. planipennisi and 1200 S. agrili, and the one year release sites each received 400 T. planipennisi and 200 S. agrili. In southern Maryland the two year release sites each received 6300 T. planipennisi and 3000 S. agrili, and the one year release sites each received 800 T. planipennisi and 500 S. agrili. To establish our EAB cohorts we attached 30 eggs to each of 10 trees per site (for a total of 3600 eggs), then covered half of the trees with mesh fencing to exclude woodpeckers (enabling us to quantify the effects of woodpecker predation on EAB). In the spring of 2013, all 120 of our study trees were debarked and the fates of the EAB cohorts were determined. Findings from this study so far suggest that woodpeckers do not have a significant effect on EAB population growth at newly infested sites, but woodpecker predation on EAB larvae at these sites could hinder the establishment of introduced parasitoids. An additional 16 trees were also felled and debarked in full in spring 2013 to collect data on EAB mortality factors for inclusion in a general survey across multiple study sites. Currently for the summer of 2013, we are continuing our EAB life table research, and have started to establish experimental cohorts of larvae at the same 12 sites again, but this year we have not been able to include a woodpecker exclusion treatment (and therefore we are using only 60 trees in total) because of budget cuts. Additionally, to improve future monitoring of the EAB egg parasitoid Oobius agrili dispersal, field trials of different methods are underway.