The Fate of Ornamental White Fringetree Through the Invasion Wave of Emerald Ash Borer and Implications for Novel Host Use by This Beetle

Emerald ash borer (EAB, Agrilus planipennis Fairmaire [Coleoptera: Buprestidae]) is a wood boring beetle that is an invasive pest of ash trees (Fraxinus spp.) in North America. In 2014, it was reported that EAB had infested white fringetree (Chionanthus virginicus L. [Lamiales: Oleaceae]) in Ohio and was since found to have infested this species across its invasive range. In 2018, we reexamined 166 white fringetrees in Illinois, Indiana, Ohio, and Pennsylvania that had been previously examined for EAB attack in 2015 to determine their fate. We assessed tree health and EAB infestation in each tree, assigned an infestation status of newly, continuously, not reinfested, or never infested, and compared the trees’ current status to their 2015 status. This assessment was done to determine whether their health and infestation status had changed through the EAB invasion wave. We found that attack rates declined: 26% of trees were infested in 2015 whereas only 13% were in 2018, likely coinciding with declining beetle populations in the area. Overall tree health improved for trees that were not reinfested by EAB after a record of attack in 2015, suggesting that they can survive and recover from EAB attack. Conversely, health declined for newly and continuously infested trees, indicating that they became stressed from EAB attack. Although the majority of the trees survived the invasion wave, several were removed from various sites due to EAB attack suggesting that white fringetree varies in its resistance and tolerance to attack. As beetle populations continue to expand geographically, infestation rates will likely increase and health of white fringetrees will decrease with the EAB attack wave, especially as EAB reaches denser populations of fringetrees.

Existence and asymptotic behavior of invasion wave solutions in temporally discrete diffusion systems with delays

This paper is concerned with the existence and asymptotic behavior of invasion wave solutions for a time-discrete delayed diffusion competitive system with non-quasi-monotone conditions. The existence of invasion wave solution is investigated by applying upper–lower solutions method and Schauder’s fixed point theorem. Further, with the help of Ikeharaś theorem, we establish the exponential decay asymptotic behavior of traveling wave solutions at the minus/plus infinity.

Condition of green ash (Fraxinus pennsylvanica) overstory and regeneration at three stages of the emerald ash borer invasion wave

Assessing emerald ash borer (Agrilus planipennis Fairmaire) impacts in North American forests is essential for projecting future species composition of stands invaded by this phloem-feeding pest. We surveyed all species of overstory trees and regeneration in 2010 and 2011 in 24 forested sites with a major component of green ash (Fraxinus pennsylvanica), representing the Core, Crest, and Cusp of the A. planipennis invasion wave across southern Michigan. By 2011, an average of 78.6% ± 0.10%, 44.8% ± 0.11%, and 19.8% ± 0.07% of overstory ash trees representing 87%, 57%, and 14% of the total ash basal area had been killed in Core, Crest, and Cusp sites, respectively. Green ash seedlings, saplings, and recruits were abundant in all sites, but newly germinated ash seedlings were absent in Core sites and scarce in Crest sites. Canopy gaps resulting from current ash decline and mortality increased available photosynthetically active radiation (PAR) and sapling growth in Crest sites, but PAR was low in Core and Cusp sites. Lateral ingrowth of non-ash overstory trees has largely filled canopy gaps in Core sites, and there was little evidence of green ash recruitment into the overstory. Green ash appears unlikely to persist as a dominant species in forests invaded by A. planipennis.