New agent of wood alteration in poplar (populus nigra)

Megaplatypus mutatus Chapuis (Coleoptera: Platypodidae) (Fig.1), an exotic insect introduced from the neotropical region, is an emerging pest in Southern Italy (Tremblay et al., 2000; Allegro & Griffo, 2008). The platypodid beetle is a primary and polyphagous pest infesting only healthy standing trees of several botanical species (Corylus, Prunus, Juglans, Pyrus, Malus, Populus, etc.); cut wood or “sick” trees are not colonized. M. mutatus is a xylomicetophagous species (=Ambrosia beetle). In Campania it may cause dramatic damages, especially in commercial plantations of Populus nigra. Male platypodid infest new trees primarily in late spring: coarse boring dust can be observed on attacked trees, which usually exude sap through the entrance holes. Females join the males soon after a successful attack and complete most of the typical galleries, excavated on a transversal plane through the xylem, as they lay eggs. The young larvae feed on symbiontic fungus and the last instant also on wood, boring each a vertical pupal chamber. Economic losses in poplar woods are due to stem fracture caused by the presence of parental gallery systems, the massive diffusion of the fungi in the xylem and wood alteration (Fig. 2). From a poplar wood infested by M. mutatus in Campania (Fig. 3), a fungus responsible of a chromatic wood alteration has been identified. Wall tissues from M. mutatus galleries coated with a firm mycelium were sampled (Fig. 4,5). Several fungal colonies with a red mycelium and a strong coloration on PDA have been isolated. All the red strains belong to the genus Verticillium spp. (Fig. 6). The fungus establish a physical contamination with the platypodid and are massively present in the brood galleries. To our knowledge, this is a new association and up to now the possible role of this relationship is unknown. A typical symbiontic species recorded for M. mutatus in Argentina is an ascomycota of the genus Raffaelea (Jones & Blackwell, 1998; Gebhardt & Oberwinkler, 2005). Differences in environmental conditions and in ecological interactions may explain the presence of Verticillium spp. in the galleries of M. mutatus on poplar in Campania. Biological investigations in order to characterize the beetle-fungus association are in progress.