THE PINE SHOOT BEETLE TOMICUS-PINIPERDA AS A VECTOR OF BLUE STAIN FUNGI TO WINDBLOWN PINE

After the great gale of 1987, the role of the pine shoot beetle, Tomicus piniperda, as a vector of blue stain fungi to windblown pine in southern England was examined by macerating adult beetles and culturing the macerate on various agar media. Isolations were also made from pine tissue associated with beetle galleries and tunnels. Using data from between three and nine sites, it was found that 17 per cent of the overwintered adult beetles were carrying fast-growing Leptographium spp. as they began to construct breeding galleries in spring 1988. More than half the new generation of adult beetles were contaminated with these fungi when they emerged in June-July 1988, but this proportion dropped as the life cycle of shoot-feeding and overwintering progressed. It averaged 26 per cent at the time of brood gallery construction in spring 1989. Isolations made from pine tissue around the galleries also showed changes in the frequency of blue stain fungi. Of early brood galleries 25 per cent yielded Leptographium, while the figure for late galleries was 51 per cent. These results were consistent with the direct introduction of Leptographium by the parent beetles into some galleries, and the subsequent rapid hyphal growth of the fungus within the tree to colonize tissue adjacent to other galleries. The principal species identified was L. wingfieldii. However, L. lundbergii, L. huntii, L. procerum and an unidentified Leptographium species were occasionally recorded, both on the beetles and in the trees. Graphium species were quite common also. In addition, the black yeasts, Hormonema dematioides and Aureobasidium pullulans, were frequently present, particularly in the pine shoot samples.