Drought stress increased survival and development of emerald ash borer larvae on coevolved M anchurian ash and implicates phloem‐based traits in resistance

Emerald ash borer ( Agrilus planipennis Fairmaire, EAB ) is causing widespread ash ( Fraxinus spp.) mortality as it invades N orth A merica and E astern E urope. Resistance of its coevolved hosts, including M anchurian ash ( Fraxinus mandshurica R upr.), is considered to limit EAB outbreaks and ash mortality in its native A sia, although an understanding of resistance mechanisms is still developing. Such knowledge may facilitate breeding for resistance and management of EAB in its invaded ranges. In the present study, controlled egg inoculations were used to investigate resistance mechanisms impacting larval performance, as well as to characterize the effects of water and nutrient availability on inter‐ and intra‐specific variation in resistance phenotypes based on larval outcomes. Larval survival and growth rates were lower on coevolved M anchurian ash than on evolutionarily naïve white ash ( Fraxinus americana L .). Water stress decreased tree growth and resistance of M anchurian ash to EAB , although it had little effect on resistance of the already highly susceptible white ash. High nutrient availability increased tree growth but had no effect on larval performance. These results show that the higher resistance of M anchurian ash to EAB is conferred by phloem traits that decrease larval performance, in addition to lower oviposition preference.