The emerald ash borer, Agrilus planipennis Fairmaire, has destroyed millions of ash trees (Fraxinus spp.) in North America since first identified in Detroit in 2002. With species of ash distributed throughout North America, it is easy to speculate the extinction of all susceptible species of ash on the continent given a lack of physical, environmental, or climactic barrier for dispersal of the insect. We investigated water balance characteristics of emerald ash borer ova by using gravimetric methods in an effort to measure their response to heat- and water-stress and explore possible influences this stress may have on the ecology and physiology of the ovum. We also explored the possible water balance benefit of a peculiar, “clustering,” oviposition behavior, as well as the difference in responses to stress between ova from a laboratory colony and ova from two wild populations. We found no evidence of water vapor absorption as a water balance strategy; rather enhanced water retention, resistance to desiccation, and viability with low water content were important survival strategies for these ova. Surface lipids resist thermal breakdown as indicated by ova having no detectable critical transition temperature, maintaining their water-proofing function as temperature rises. The observed “clustering” behavior had no desiccation-avoidance benefit and ova from the wild populations behaved almost identically to the ova from the lab colony, although the lab ova were slightly larger and more sensitive to dehydration. Given this new information, there appears to be no heat- or water-stress barriers for the dispersal of this devastating pest at the ovum stage.
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