Attraction of Walnut Twig Beetle Pityophthorus juglandis (Coleoptera: Curculionidae) to the Fungus Geosmithia morbida

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Abstract
Geosmithia morbida causes thousand cankers disease of Juglans nigra and it is transmitted by the walnut twig beetle (WTB, Pityophthorus juglandis). Along with WTB, an ambrosia beetle, Xyleborinus saxeseni, is commonly associated with thousand cankers disease in the later stages of J. nigra decline, although X. saxeseni is not a known vector of G. morbida. We initiated studies to determine whether WTBs or X. saxeseni were attracted to volatiles produced by G. morbida and other bark fungi in a laboratory choice-test setting. There was no difference between the numbers of emerged WTB adults that were collected in tubes containing potato dextrose agar colonized by G. morbida and those in tubes containing agar only. More adult X. saxeseni were collected in tubes containing agar only compared with G. morbida. Walnut twig beetle larvae migrated more frequently toward an agar plug colonized by G. morbida and Fusarium solani compared with an un-colonized agar plug. No larval preference was observed when agar plugs colonized by F. solani and G. morbida, or G. morbida and Penicillium solitum, were placed in the same petri dish. These results suggest that WTB larvae are attracted to bark fungi in general, but not specifically to G. morbida. Accepted 27 June 2014. Published 13 August 2014.

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