Modest Effects of Host on the Cold Hardiness of Emerald Ash Borer †

Lindsey Christianson,Robert Venette

doi:10.3390/f9060346

Abstract

The emerald ash borer, Agrilus planipennis Fairmaire, is invading North America and Europe but has not yet reached its ultimate distribution. Geographic differences in host availability and winter temperatures might affect where this species will occur. In central North America, black ash (Fraxinus nigra) is more abundant than green ash (F. pennsylvanica) at northern latitudes, but much of our current understanding of A. planipennis cold tolerance is based on observations of overwintering larvae from green ash. The effects of black and green ash on the cold hardiness of A. planipennis larvae were measured over three winters. Supercooling point, the temperature at which insect bodily fluids spontaneously begin to freeze, was marginally greater for larvae from artificially-infested black ash than green ash in one trial, but not in three others. Host species also did not consistently affect mortality rates after larval exposure to subzero temperatures, but larvae from black ash were less cold hardy than larvae from green ash when there were differences. Comparisons of mortality rates among chilled (unfrozen) and frozen larvae indicated that overwintering A. planipennis larvae are primarily freeze avoidant, and this cold tolerance strategy is unaffected by host. All of our studies suggest that A. planipennis larvae from black ash are not more cold hardy that larvae from green ash. Where temperatures annually decline below ~−30 °C, overwintering morality may substantially affect the population dynamics and future impacts from this invasive alien species.

Highlights

The invasions of North America and Eurasia by the emerald ash borer, Agrilus planipennisFairmaire (Coleoptera: Buprestidae), portend significant ecological, economic, and social impacts, many of which have been realized and others theorized
Fraxinus nigra Marsh., blue ash, F. quadrangulata Michx., green ash, F. pennsylvanica Marsh., and white ash, F. americana L. have been colonized naturally by this insect in eastern North America [1,2,3], and tens of millions of ash trees have died from infestation [4,5,6]
Supercooling points occurred at warmer temperatures in 2011 (November) than in 2013 (January) for larvae from black ash and green ash

Summary

Introduction

The invasions of North America and Eurasia by the emerald ash borer, Agrilus planipennis. Fairmaire (Coleoptera: Buprestidae), portend significant ecological, economic, and social impacts, many of which have been realized and others theorized. Fraxinus nigra Marsh., blue ash, F. quadrangulata Michx., green ash, F. pennsylvanica Marsh., and white ash, F. americana L. have been colonized naturally by this insect in eastern North America [1,2,3], and tens of millions of ash trees have died from infestation [4,5,6]. Where emerald ash borer has invaded, significant economic costs associated with mitigative treatments, tree removals, and tree replacements and lost home equity have been incurred [10,11]. Losses of ash trees may be associated with an increase in cardiopulmonary disease in urban areas [12] and threaten culturally significant uses of the resource by some Native. The ultimate magnitude of these impacts depends, in part, on the final geographic distribution of the species

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