Emerald Ash Borer: the Complexities of a Catastrophic Invader

Transcription

1 Emerald Ash Borer: the Complexities of a Catastrophic Invader Deborah G. McCullough, Professor Dept. of Entomology & Dept. of Forestry Michigan State University Fraxinus sp.

2 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 planipennis 2017: EAB in 31 states & 3 Canadian provinces

3 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 eggs per female; range is 2 to 268 eggs.

4 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. L2, L3 & L4 larvae in Sept. Gallery Prepupal larvae

5 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).

6 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.

7 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.

8 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 & funnel traps in ash trees Double-decker Girdled trees - debarked

9 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. N W NW NE E Probability not detected N Ash Phloem Area (m 2 ) m SW SE Years after establishment W E S S 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

10 Adult EAB host preference varies among ash species Preferred & vulnerable Less preferred Black ash Green ash White ash Blue ash Anulewicz et al. 2007; Rebek et al. 2007; Chen & Poland 2010, Tanis & McCullough 2012, 2015; Robinett & McCullough 201X

11 Green ash condition at 3 stages of the EAB invasion Cusp - SW 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). Crest - central Core - SE

12 Live as basal area (m² per ha) Average percent of green ash basal area that was alive declined as EAB invasion progressed (n=8 sites per stage) Core Crest Cusp % 5% 63% 45% 95% 85% Live basal area (1035 ash trees) c z No ash seedlings with cotyledons in Core sites b y a x Core Crest Cusp Burr & McCullough Can J For Res.

13 PAR as a percentage of full sun 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? 20% 16% Mean ( SE) PAR a 12% 8% 4% b b 0% Core Crest Cusp

14 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 From 2007 to 2013, 8 ash were felled & debarked annually to monitor EAB larval density. 800 m 400 m 50 x 50 m grids

15 Density of EAB larvae increased exponentially. Few green ash >10 cm DBH were alive in Average (+SE) Live EAB larvae per m No. live green ash inventoried J3 J5

16 Green ash saplings & recruits are abundant J3 J5 No. ash recruits per ha Percent alive in % 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.

17 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

18 Ash trees in landscapes generally killed if not protected with effective insecticides. Dead trees are hazards. Tree removal is costly & unpleasant. Ohio Saginaw, MI Shields, MI Lansing, MI Minnesota

19 Systemic insecticide products & application methods are much improved compared to the early days of EAB TreeAzin TREE-äge Safari basal trunk spray Imidacloprid soil drench; (2x rate) TREE-äge

20 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

21 Relatively new systemic insecticide options Products (active ingredient) TREE-äge - trunk injection (emamectin benzoate) TreeAzin - trunk injection (azadirachtin) Azasol - trunk injection (azadirachtin) Safari, Transtect basal trunk spray (dinotefuran) Imidacloprid products - 2x rate spring soil drench or soil injection Treat 2-3 years 1-2 years 1-2 years 1 year 1 year

22 Information on insecticides for EAB & ash protection available free at 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 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

23 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 Treating mature landscape trees retains ecosystem services & property values. Allows for long-term planning & staged replacement of ash trees in municipalities (e.g., year period).

24 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.

25 SLAM Pilot Project: (> 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 Mercader et al. 2013, 2015, 2016 McCullough SLAM webinar

26 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.

27 Native Parasitoids Native parasitoids, particularly Atanycolus spp., are increasingly common. Native parasitoids are clearly learning to search ash trees for EAB larvae. A. cappaerti A. cappaerti Highest parasitism rates usually in heavily infested trees (attraction to stress volatiles). Potentially more important in the EAB Core, post-invasion? Phasgonophora sulcata

28 Asian parasitoids - Classical biocontrol for EAB USDA APHIS, ARS & USFS are spending $ millions on imported parasitoids. First releases were in MI in APHIS releasing >280,000 wasps annually since Spathius agrili S. galinae Tetrastichus planipennisi Oobius agrili (egg parasitoid)

29 Classical biocontrol for EAB Research begins in native range to assess life history, hosts, reproduction, develop rearing methods, etc. Insects are imported & held in quarantine labs in US for further host range testing with North American species. EAB parasitoids - Environmental Assessment & Federal Register announcement in 2007 Large scale parasitoid rearing occurs at USDA APHIS facility in Brighton, MI State approval typically requested for releases Ideally, releases are followed by evaluations to assess establishment (MapBiocontrol website) but doesn t always occur.

30 Classical biocontrol for EAB Spathius agrili Cold tolerance poor. Host specificity? Tetrastichus planipennisi Good disperser but tiny ovipositor Oobius agrili Difficult to study in the field Spathius galinae Too soon to assess Issues: Rearing sustainability? Requires infested ash logs for EAB rearing; No adequate artificial diet. Parasitoids have not slowed EAB population growth or ash mortality rates in newly infested sites or post-invasion sites. Little evidence of subcortical insect populations that are regulated by predators or parasitoids. But few other options for ash in North American forests.

31 Integrating tactics for EAB systemic insecticides & biocontrol are compatible Additive or even superadditive effects could occur: (1) Tactics target different life stage of the pest (2) Insecticides do not interfere with natural enemies (3) Natural enemies engage in non-random searching for their prey or hosts. Barclay & Li Theor. Pop. Ecol. Berec et al Trends Ecol. Evol. Sucking et al Environ. Entomol.

32 Other questions from the Committee Focus on the insect or the host? Many Fraxinus species occur in North America ( 18 species) & Europe. Host preference or host suitability varies, but EAB probably can develop on all ash species. In its native range, EAB is a secondary pest. Co-evolved resistance breaks down - stressed trees are attractive & vulnerable to EAB. Reducing EAB success (e.g., host-finding, reproduction, dispersal ability?) would presumably benefit all ash species.

33 Other questions from the Committee Focus on the insect or the host? Contrast with hemlock woolly adelgid (HWA) (Adelges picea) HWA: Passive dispersal - no flight; Immature life stages dispersed via wind, birds); No host selection; No mating (parthenogenic) Two hosts of concern (Tsuga canadensis, T. caroliniana), while western hemlock (T. heterophylla) is relatively resistant. Insect predators help control HWA populations in Pacific NW. Some amount of host resistance is generally needed for effective biocontrol.

34 Other questions from the Committee HWA mutation rate: On average, a mutation arises each generation at every base 10 pair in the entire A. tsugae genome within infested areas of only 40 ha (Butin et al. 2005). Selection for cold tolerance observed in New England Altering the host(s) to enhance HWA resistance (and perhaps biocontrol) seems more likely to be successful than modifying the pest.