CONICET | Buscador de Institutos y Recursos Humanos

Megaplatypus mutatus (=Platypus mutatus), an Ambrosia beetle (Platypodidae, Platypodinae, Platypodini) native to South America, is a main forest pest that attacks live standing trees, affecting commercial poplar and other broadleaf plantations. M. mutatus has been accidentally introduced in Italy in 1998 detected in Populus canadensis in the Caserta province in the Campania region. The risk of dispersion and potential damages are of big concern for local and European authorities who recommended to regulate it as a quarantine pest in 2007. The attack is initiated by pioneer males selecting a host tree to build a short nuptial gallery, from which they attract females using a sexual pheromone composed mainly by (+) 6-methyl-5-hepten-2-ol ((+)-sulcatol) and 6-methyl-5-hepten-2-one (sulcatone). Following copulation, they extend their gallery digging deeply into the host xylem in order to lodge their new breed. Apparently these galleries weaken the trunks of trees, causing them to break under extreme stress. Additionally, the quality of the wood is seriously affected by the dark stained tunnels caused by the Ambrosia mycelium of the associated symbiotic fungi Raffaellea santoroi transported by the beetle in specialized structures named micangia. This association has been widely reported in other ambrosia and bark beetles, but the nature of these associations and the role of the fungal composition remain mostly unknown. In the present work the mycobiota associated to the male nuptial chamber of M. mutatus was characterized and the phylogenetic relationships between different hosts and localities investigated. A total of 91 isolations were made, obtaining in axenic culture 47 cepae, mostly belonging to the genera Raffaelea (von Arx & Hennebert emend Batra) and Ambrosiella (von Arx & Hennebert emend Batra). The phylogenetic relationships hypothesized are discussed. The cepae obtained were identified morphologically and a subset was sequenced by DNA nuclear extraction and amplification with NS1 and NS6 primers. Data analysis was performed with maximum parsimony under static and dynamic homologies. We also perform a tomography study of bolts with M. mutatus infestations in order to investigate the extension of the damage to the host. The image analysis shows a radiographic alteration of the host tissues far beyond the M. mutatus gallery, probably the reason of the tree breakage during wind felling.

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