Research Abstract |
Biological and ecological traits of three woodwasp species, Sirex nitobei, Urocerus japonicus and Xeris spectrum, were investigated to clarify their pattens of resource utilization and reproductive strategies. The oviposition activity of Sirex nitobei was affected greatly by the host tree conditions : the proportions of oviposition on the fresh logs within 0-3 days and the old ones over 25 days after tree felling were much lower than those on the medium (4-24days) logs. X.spectrum, which has no symbiotic fungi with its body, also exhibited the oviposition activities only for the fresh logs inoculated artificially with Amylostereum areokatum or A.chailletii which were associated symbiotically with other woodwasp species. Urocerus japonicus, with a potential risk of outbreak in commercial plantations of Crytomeria japonica and Chamaecyparis obtusa, exhibited its peak emergence around July and ovipositional preference for the logs within one month after tree felling. The association between blue stain fungi and Ips cembrae was examined in Japanese larch and Japanese red pine trees. The blue stain fungi, Ophiostoma piceae and Lepitographium sp., were isolated from the body surface, which suggests that this beetle species was a vector of these fungi. The fact that O.piceae was consistently isolated with high frequency from both adults and galleries also suggested that this fungus species would be the principal blue stain fungus infecting the beetle attacked trees of Japanese larch. An inoculation experiment testing the pathogenicity of a blue stain fungus, Ceratocystis (Ophiostoma) piceae, to young Japanese red pine trees showed that under stressed conditions, the Japanese red pine trees were greatly damaged by the fungal invasion, with larger necrotic lesions, more reduced water pressure potential of the xylem and higher mortality than uninfested ones.
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