Abstract
Emerald ash borer (EAB), (Agrilus planipennis Fairmaire), first identified in 2002 in southeast Michigan, has caused catastrophic ash (Fraxinus spp.) mortality in forests within the core of the invasion and has spread to 35 states and five Canadian provinces. Little is known about persistence and densities of EAB populations in post-invasion sites after most ash trees have died. We monitored EAB populations from 2014 to 2016 using double decker (DD) traps set in the midst of white ash (F. americana) trees in 30 post-invasion sites in southeast and south-central Michigan. Two DD traps were deployed at each site. One trap had a dark green upper prism and light purple lower prism, both baited with cis-3-hexenol lures. The other had two dark purple prisms baited with cis-3-hexenol on the upper prism and Manuka oil on the lower prism. In 2014 and 2016, size and condition of ash trees were recorded and area of live white ash phloem was estimated in an 18-m-radius plot centered around each of the DD traps. Area of live white ash phloem per site ranged from approximately 24 to 421 m2 in 2014 and from 24 to 411 m2 in 2016. Canopy condition of live white ash trees generally improved; 65% and 89% of the trees had healthy canopies (<20% dieback) in 2014 and 2016, respectively. Traps in 28, 29 and 30 of the sites captured a total of 580, 585, and 932 EAB adults in 2014–2016, respectively. Area of live ash phloem explained relatively little of the variation in total EAB captures in all three years. Low trap catches, along with relatively stable canopy conditions and continued abundance of live white ash, indicate that EAB populations remain below the carrying capacity of the sites, and ash phloem availability is not a limiting factor for EAB abundance. Further monitoring to track both EAB dynamics and tree condition is needed to determine the long-term outlook for white ash in these sites.
Highlights
Emerald ash borer (EAB) (Agrilus planipennis Fairmaire) (Coleoptera: Buprestidae), a phloem-feeding beetle native to Asia, was first identified in 2002 in North America when adult beetles were collected from dying ash (Fraxinus spp.) landscape trees in the Detroit metropolitan area in southeast Michigan, USA [1,2]
Along with relatively stable canopy conditions and continued abundance of live white ash, indicate that EAB populations remain below the carrying capacity of the sites, and ash phloem availability is not a limiting factor for EAB abundance
In plots established in the original core of the EAB invasion in southeast Michigan, 80 to 99% of green ash (F. pennsylvanica Marsh.), black ash (F. nigra Marsh.), and white ash (F. americana L.) trees in forest overstories had died by the early- to mid-2000s [8,9,10]
Summary
Emerald ash borer (EAB) (Agrilus planipennis Fairmaire) (Coleoptera: Buprestidae), a phloem-feeding beetle native to Asia, was first identified in 2002 in North America when adult beetles were collected from dying ash (Fraxinus spp.) landscape trees in the Detroit metropolitan area in southeast Michigan, USA [1,2]. An extensive dendrochronological study spanning 1.5 million ha showed that EAB had killed ash trees in southeast Michigan by 1998, indicating it likely became established in this area by the early 1990s [3]. Hundreds of millions of ash in forests, rural and urban areas have been killed by EAB, which has become the most destructive and costly invasive forest insect in North America [5,6,7]. In plots established in the original core of the EAB invasion in southeast Michigan, 80 to 99% of green ash (F. pennsylvanica Marsh.), black ash (F. nigra Marsh.), and white ash (F. americana L.) trees in forest overstories had died by the early- to mid-2000s [8,9,10]
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