Microbial Interactions Support the Role of Ambrosia Beetles as Potential Vectors of Dutch Elm Disease

Dutch elm disease (DED) has caused devastating pandemics in natural elm populations across Europe, North America, and Asia. The primary vectors of DED are native elm-associated bark beetles of the genus Scolytus. However, there is evidence suggesting that ambrosia beetles may also carry Ophiostoma novo-ulmi and potentially transmit it to elm trees. In this study, we explored microbial interactions and host selection mechanisms that could support the role of ambrosia beetles as vectors of O. novo-ulmi. Our study showed that females of Anisandrus dispar, Xyleborinus saxesenii, Xylosandrus crassiusculus, and Xylosandrus germanus emerging from both DED-infected and healthy elm logs carried O. novo-ulmi DNA. Furthermore, we showed that none of the tested ambrosia beetle fungal symbionts was adversely affected by O. novo-ulmi, while Dryadomyces spp. and the bacterial symbiont Erwinia sp. 1C4 partially restricted or inhibited O. novo-ulmi growth without fully suppressing it. Overall, these findings provide additional evidence supporting the potential role of ambrosia beetles as vectors of DED and emphasize the need for further research on this understudied insect-pathogen relationship.