In 2014, Cipollini discovered that the ash-killing emerald ash borer, Agrilus planipennis, was capable of feeding and completing development on white fringetree, Chionanthus virginicus, a native North American tree that is used as an ornamental. Subsequent studies have revealed that this phenomenon is widespread and may be due to shared chemical characteristics of white fringetree with susceptible ash species. Given its ability to use white fringetree, we have been examining other close relatives for their susceptibility to emerald ash borer, with potentially important implications for the spread, impacts, and persistence of emerald ash borer in North America and beyond. In this study, we examined the susceptibility of cultivated olive, Olea europaea, to emerald ash borer, Agrilus planipennisin a series of controlled laboratory tests. Cultivated olive is a Mediterranean native that is grown in the southeastern and western U.S. It will be contacted by emerald ash borer within 1-2 years in the U.S. and within a decade in the Mediterranean basin.
In two short-term bioassays, we found significant feeding and survival of first instar larvae on small diameter stems from both potted and field grown trees. In a long-term bioassay utilizing larger stems from a field-grown tree (cv. ‘Manzanilla’), we found that 48% of larvae that had emerged from eggs used to inoculate stems were recovered alive, many as larvae or prepupae during periodic debarking of a subset of stems. Three intact stems were overwintered artificially, followed by a return to room temperatures. Four live adults emerged from these stems and a pupa and an additional prepupa were discovered after debarking them. This degree of success is lower than expected on susceptible North American ash trees but it is higher than expected on resistant native hosts of emerald ash borer. Cultivated olive now joins white fringetree as one of only two species outside of the Fraxinus genus that has been shown capable of supporting the complete development of emerald ash borer from the egg stage to adult. Future studies will be aimed at determining oviposition rates of emerald ash borer on olive trees, as well as examination of genotypic and environmental variation in their susceptibility to emerald ash borer.