The black twig borer, Xylosandrus compactus (Eichhoff), is a globally invasive ambrosia
beetle. In recent years, X. compactus has attacked healthy plant branches and caused
economic damage to ornamental trees in many locations worldwide, including in Shanghai
city. In this study, two fungal species were consistently isolated from the beetle
mycangia and its galleries. One is Ambrosiella xylebori, a known symbiont, the other
one is Thyridium lauri, a recently described species whose association with the beetle
has not been reported from Asia, it's native region. The two fungal species were recorded
as symbiotic fungi associated with X. compactus in several collections. In order to
clarify the role of symbiotic fungi during the X. compactus attack on the tree branches,
the pathogenicity of both fungi was tested on eight ornamental trees, including Magnolia
grandiflora, M. denudata, Platanus acerifolia, Acer palmatum, Cinnamomum camphora,
Cerasus yedoensis, Liquidambar formosana, and Quercus texana. Our results showed that
the two fungal species had low damage potential, at least on young ornamental trees.
Therefore, the killing of the twigs is attributable to the disruption of vascular
tissues by beetle drilling, rather than to the pathogenicity of fungal associates.
This suggests that Thyridium lauri does not act as a pathogen on its native host trees,
as it does on susceptible laurels in invaded regions.
