Emerald Ash Borer: the Complexities of a Catastrophic Invader Fraxinus sp. Deborah G. McCullough, Professor Dept. of Entomology & Dept. of Forestry Michigan State University
EAB is native to China, Korea, Mongolia & E. Russia. Likely arrived in solid wood packing material from Asia. ≈1990 : EAB becomes established in southeast Michigan. 2002 : EAB “discovered” & identified as Agrilus planipenni s 2017: EAB in 31 states & 3 Canadian provinces www.emeraldashborer.info
EAB adults select hosts for feeding & egg-laying Egg hatching Beetles feed on ash foliage throughout their 3-6 week life span. Oviposition begins 2-3 weeks after emergence. Probably 50-60 eggs per female; range is 2 to 268 eggs.
Larvae feed on phloem & cambium in S-shaped galleries from mid summer to fall. Complete 4 instars. Most larvae overwinter as prepupae in outer sapwood or outer bark. Prepupal larvae L2, L3 & L4 Gallery larvae in Sept.
Pupation (≈14 days) Pupation occurs in spring. New adults emerge from D-shaped exit holes beginning around 450 DD 50 F (mid May to June).
As larval density builds, galleries disrupt translocation. Woodpeckers prey on larvae (mostly in winter) & holes are often the 1 st sign of EAB. Eventually, foliage thins, branches die, bark cracks & epicormic sprouts appear.
EAB is already the most destructive forest insect to ever invade North America. Hundreds of millions of ash ( Fraxinus spp.) in landscapes & forests have been killed. Sept. 2017 : Ash is “red - listed” by IUCN.
Very difficult to detect, delimit & survey EAB 1. No external signs or symptoms at low larval densities. 2. Two-year EAB life cycle in healthy, newly-infested trees. 3. No long range pheromones. 4. Girdled & debarked ash most effective, but not often used. 5. Canopy traps & lures are not highly effective. USDA APHIS prism & Girdled trees - debarked funnel traps in ash trees Double-decker
Adult EAB dispersal: Most females lay eggs within 100 meters of their emergence point. But… a few females (maybe 1 to 5%?) disperse 1-5 km (?). This “long range” dispersal is unpredictable. Probability not detected NW NE W SW SE Years after establishment N Actual EAB distribution is likely 4-6 km or more beyond the detection threshold, even 6 years after establishment. Satellite populations “simmer” for at least 4 years before detection. Mercader et al. 2009, 2011, 2012 McCullough et al. 2011; Siegert et al. 2010
Adult EAB host preference varies among ash species Preferred & Less preferred vulnerable Green ash Black ash White ash Blue ash Anulewicz et al. 2007; Rebek et al. 2007; Chen & Poland 2010, Tanis & McCullough 2012, 2015; Robinett & McCullough 201X
Green ash condition at 3 stages of the EAB invasion Core: Southeast, near EAB origin Crest: Central; Densities peaking Cusp: Southwest; EAB more recent Green ash comprised 20-50% of the overstory in all 24 sites. Surveyed EAB density, overstory & regeneration in 1 ha areas in 2010 & 2011 (8 sites per stage). Cusp - SW Crest - central Core - SE
Average percent of green ash basal area that was alive declined as EAB invasion progressed (n=8 sites per stage) Core Crest Cusp 2010 2011 2010 2011 2010 2011 8% 5% 63% 45% 95% 85% Live basal area (1035 ash trees) No ash seedlings with 8 cotyledons in Core sites 2010 Live as basal area (m² per ha) c z 6 2011 4 b y 2 a x 0 Core Crest Cusp Core Crest Cusp Burr & McCullough. 2014. Can J For Res.
PAR intercepted by other overstory species in Core sites Photosynthetically active radiation (PAR) was lower in Core & Cusp than in Crest sites. Lateral in-growth of non-ash tree canopies filled most canopy gaps & intercepted PAR in Core sites. Ash recruits require sun to reach the overstory. Green ash persistence? Mean ( SE) PAR - 2011 20% a PAR as a percentage of full sun 16% 12% 8% b b 4% 0% Core Crest Cusp
Jasper: Long-Term Evaluation of EAB & Green Ash Green ash were inventoried (by DBH class) in 2007 in 2 sites, each 16.2 ha, then re-surveyed in 2015. From 2007 to 2013, ≥ 8 ash were felled & debarked annually to monitor EAB larval density. 800 m 400 m 50 x 50 m grids
Density of EAB larvae increased exponentially. Few green ash >10 cm DBH were alive in 2015. Average (+SE) Live EAB larvae per m 2 No. live green ash inventoried 90 2500 80 2007 2000 70 60 2015 1500 50 40 1000 30 500 20 10 0 0 J3 J5 2007 2008 2009 2010 2011 2012 2013
Green ash saplings & recruits are abundant. 2015 J3 J5 No. ash recruits per ha 784 1393 Percent alive in 2015 46% 58% Size & persistence of canopy gaps, plus EAB dynamics, will determine whether young green ash reach the overstory. Green ash could be functionally lost from many sites.
Current options for managing EAB & ash trees A. Remove infested trees (or pre-salvage ash timber) B. Insecticides (systemics) C. Girdled trees: Function as “sinks” to attract EAB adults then debarked, sectioned or destroyed to kill larvae. D. Natural enemies & biological control E. Integrated management – combinations of A-D
Ash trees in landscapes generally killed if not protected with effective insecticides. Dead trees are hazards. Tree removal is costly & unpleasant. Ohio Shields, MI Saginaw, MI Lansing, MI Minnesota
Systemic insecticide products & application methods are much improved compared to the early days of EAB TreeAzin TREE-äge Safari basal trunk spray Imidacloprid soil TREE-äge drench; (2x rate)
Emamectin benzoate (TREE-äge): Trunk injection in spring provides 3 years of nearly 100% EAB control, even at the lowest application rate. Control TREE-äge
Relatively new systemic insecticide options Products (active ingredient) Treat TREE-äge - trunk injection 2-3 years (emamectin benzoate) TreeAzin - trunk injection 1-2 years (azadirachtin) Azasol - trunk injection 1-2 years (azadirachtin) Safari, Transtect – basal trunk spray 1 year (dinotefuran) Imidacloprid products - 2x rate 1 year spring soil drench or soil injection
Information on insecticides for EAB & ash protection available free at www.emeraldashborer.info Avoid neo-nic applications to soil if flowering plants are near the tree. Otherwise, few non-target impacts of systemic insecticides used on ash. All aspects of insecticide registration are regulated by EPA under FIFRA. Effects of EAB insecticide treatments on pollinators. EAB University Webinar, Oct. 2017. Dr. Reed Johnson, Dept of Ent., OSU Risk assessment of imidacloprid use in forest settings on the aquatic macroinvert. community . Environ. Tox. Benton et al. 2017.
Economics favor treating ash trees; much less costly & disruptive than removals. Kovacs et al. 2010; 2014; McCullough & Mercader 2012; McKenney & Pedlar 2012; Sadof et al. 2017; Vannatta et al. 2012 Treating mature landscape trees retains ecosystem services & property values. Allows for long-term planning & staged replacement of ash trees in municipalities (e.g., 20-30 year period).
Forested settings: systemic insecticides are rarely used. Widespread use limited by costs & per acre restrictions. EA’s (environmental assessment) were prepared for national forest lands (e.g., for SLAM Pilot Project). Some insecticide use by NPS, state DNRs, etc. to protect individual trees in campgrounds, walkways, etc. EmBen - PA DCNR protects white ash in seed orchards. EmBen - some Native American tribes protect individual black ash trees for seed collection (cultural resource). Insecticide use on private forest land occurs occasionally; usually a few mature trees are protected.
SLAM Pilot Project: 2008-2012 (> 390 km 2 area) Tiny proportion of ash trees along roads were injected with EmBen. Treatment slowed EAB population growth 2+ years. Grids of girdled trees used for EAB detection & as “sinks.” Girdled trees slowed EAB pop. growth & spread for 1 year. McCullough et al. 2015 Mercader et al. 2013, 2015, 2016 McCullough SLAM webinar - 2015
Natural Enemies & Biological Control Woodpecker Predation WP holes are often the first sign of EAB; Flecking occurs on heavily infested trees. WP predation is the major source of EAB mortality but rates are highly variable. WPs prey on late instar EAB larvae & prepupae in winter & early spring. Behavioral response to EAB by WP populations but numerical response = ? No evidence that WPs can slow EAB population growth or rates of ash mortality.
Native Parasitoids A. cappaerti Native parasitoids, particularly Atanycolus spp., are increasingly common. A. cappaerti Native parasitoids are clearly learning to search ash trees for EAB larvae. Highest parasitism rates usually in heavily infested trees (attraction to stress volatiles). Potentially more important in the EAB Core, post-invasion? Phasgonophora sulcata
Asian parasitoids - Classical biocontrol for EAB USDA APHIS, ARS & USFS are spending $ millions on imported parasitoids. First releases were in MI in 2007. APHIS releasing >280,000 wasps annually since 2012. Spathius agrili Tetrastichus planipennisi S. galinae Oobius agrili (egg parasitoid)
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