AbstractThe walnut twig beetle (WTB),Pityophthorus juglandisBlackman (Coleoptera: Curculionidae), vectors a fungus,Geosmithia morbidaKolařík, Freeland, Utley, and Tisserat (Ascomycota: Hypocreales), which colonises and kills the phloem of walnut and butternut trees,JuglansLinnaeus (Juglandaceae). Over the past two decades, this condition, known as thousand cankers disease (TCD), has led to the widespread mortality ofJuglansspecies in the United States of America. Recently the beetle and pathogen were discovered on severalJuglansspecies in northern Italy. Little is known about the extra-generic extent of host acceptability and suitability for the WTB. We report the occurrence of both the WTB andG. morbidain three species of wingnut,Pterocarya fraxinifoliaSpach,Pterocarya rhoifoliaSiebold and Zuccarini, andPterocarya stenopterade Candolle (Juglandaceae) growing in the United States Department of Agriculture-Agricultural Research Service, National Clonal Germplasm Repository collection in northern California (NCGR) and in the Los Angeles County Arboretum and Botanic Garden in southern California, United States of America. In two instances (once inP. stenopteraand once inP. fraxinifolia) teneral (i.e., brood) adult WTB emerged and were collected more than four months after infested branch sections had been collected in the field. Koch’s postulates were satisfied with an isolate ofG. morbidafromP. stenoptera, confirming this fungus as the causal agent of TCD in this host. A survey of the 37PterocaryaKunth accessions at the NCGR revealed that 46% of the trees had WTB attacks and/or symptoms ofG. morbidainfection. The occurrence of other subcortical Coleoptera associated withPterocaryaand the first occurrence of the polyphagous shot hole borer, a species nearEuwallacea fornicatusEichhoff (Coleoptera: Curculionidae), inJuglansare also documented.
Worlds of Print: The Moral Imagination of an Informed Citizenry, 1734-1835