Location: Beneficial Insects Introduction Research Unit
Project Number: 8010-22000-031-053-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 15, 2021
End Date: Sep 15, 2024
Emerald ash borer (Agrilus planipennis Fairmaire) (EAB) is a destructive invasive pest of North American ash (Fraxinus spp.) and has now spread to 35 U.S. States. To date, it has caused billions of dollars in losses to timber, recreation, and ornamental ash industries, as well as catastrophic ecological harm to forests and our landscape. More recently, this invasive beetle has also developed a new association with another North American native species, the white fringe tree (Chionanthus virginicus L.). White fringe tree is limited to the eastern United States ranging from the gulf states to New York; however, it is a commonly stocked nursery plant across the United States. Currently, it is not known if and how acquisition of white fringe trees as a new host would affect the management of EAB on North American ash trees. Several natural enemies of EAB have been introduced from Asia into North America for protection of North American ash against EAB, including one egg parasitoid (Oobius agrili), and three larval parasitoids, Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae), Spathius agrili Yang and Spathius galinae Belokobylskij (Hymenoptera: Braconidae). While the establishment and impacts of these introduced natural enemies on EAB infesting ash tree stands in natural forests have been evaluated in several Northeast States (Connecticut, Massachusetts, New York), Midwest States (Michigan, Kentucky) as well as in Mid-Atlantic state of Maryland, few studies have evaluated the establishment and impacts of these newly introduced natural enemies of EAB infesting both ash and white fringe trees in urban areas. The proposed research aims to evaluate the effectiveness of recently introduced parasitoids on EAB populations infesting both ash and white fringe trees in urban forests in the Mid-Atlantic states (Delaware and Maryland). Specifically, we will determine: (1) behavioral and population responses of recently introduced natural enemies on EAB infesting ash vs white fringe trees, and (2) field establishment rate and effectiveness of previously released natural enemies in protecting ash and white fringe trees against EAB populations. The data collected will help inform future biocontrol release efforts as well as long-term EAB management strategies to ensure ash and non-ash host tree conservation and restoration, with the ultimate goal of protecting ash- and white fringe- dependent industries.
In the laboratory experiments: Objective 1, we will use EAB-infested ash and white fringe bolts to characterize the window of EAB larval susceptibility to parasitoids as well as the host attack rate or efficiency and critical fitness parameters of the test parasitoids. Bolts of green ash and white fringe tree (~ 3 cm diam, ~15 cm length) will be cut from natural stands of healthy ash saplings and white fringes trees. Each bolt will be soaked in a 10% bleach solution for 30 min, then scrubbed with a soft-bristled brush under tap water to prevent mold growth. Bolts of similar size will each be infested with 8 viable EAB eggs (golden color, 5 – 7 days old) and then incubated for various lengths of time (5, 6, 7, 8, 9 weeks) in an environmental chamber at ~ 30oC , ~65% relative humidity, and a photoperiod of 16:8 (L:D) h prior to use for parasitoid exposures. Each EAB-infested ash or white fringe bolt of different post incubation ages will be exposed to gravid females of each parasitoid species in a ventilated cylindrical container (at ~ 1:1 host to parasitoid ratios) for ~ 1 week and then will be removed from the exposure container and placed into clean containers for rearing under normal rearing conditions (~25oC, 65% RH, and 16:8 h (L:D) photo period). Emergence of adult parasitoids from each exposed ash or white fringe bolt will be monitored and recorded weekly. After the emergence of adult parasitoid progeny is completed, all bolts will be dissected to estimate host attack or parasitism rate by test parasitoids. For tests with the egg parasitoid (O. agrili), similar parasitoid exposure experiments will be conducted except that ash and white fringe bolts containing freshly laid EAB eggs (instead of suitable stages of larvae) will be used. Objective 2, we will use sentinel host methods to evaluate field establishment and effects of natural enemies on EAB population survival and/or growth in five different locations (study sites) where these introduced parasitoids have been released or are being released in Delaware and Maryland. Sentinel host methods are effective at detecting EAB parasitism by both introduced and native North American parasitoids. For egg parasitism detection, EAB eggs freshly laid on coffee filter paper will be enclosed within a wire mesh-pouch (~20 eggs per pouch) and then deployed on ash or white fringe trees at the study sites (3 -5 mesh pouch on each tree species per sites per deployment time). The mesh hole size is large enough to allow parasitoids access to the EAB eggs while protecting those eggs against some predators (such as ants) in the field.