Modest Effects of Host on the Cold Hardiness of Emerald Ash Borer
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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.
KeywordsFraxinus nigra; Fraxinus pennsylvanica; biogeography; ecophysiology; overwintering mortality; freeze avoidance
Christianson, Lindsey; Venette, Robert. 2018. Modest Effects of Host on the Cold Hardiness of Emerald Ash Borer. Forests. 9(6): 346-. https://doi.org/10.3390/f9060346.