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ABSTRACTPreventive plantation of resistant Pinus thunbergiiseedlings is anticipated in non-epidemic areas of pine wilt disease (PWD) in Japan. The scions of resistant clones, which are required to establish a seed orchard for the production of resistant seedlings, might harbor Bursaphelenchus xylophilus(a pathogen of PWD), as they are grown in epidemic areas and artificially inoculated with B. xylophilusto verify their resistance. In this study, we analyzed within-tree distribution of B. xylophilusin inoculated grafts of a resistant P. thunbergiiclone, Yuza-155, at two different times, 7 and 19 months after inoculation. Experimental evidence using both direct extraction of nematodes and a DNA-based detection technique demonstrated that the migration and propagation of inoculated nematodes were restricted mostly within the scion stems and rootstocks. In branch samples, nematodes were detected less frequently by the DNA-based method and no live nematodes were extracted at 7 months after inoculation, whereas at 19 months after inoculation, neither of the methods detected any nematodes. Thus, the probability that the current-year shoots of this resistant clone, Yuza-155, which initiated plant growth in the season following inoculation, are infected with B. xylophilusis quite low. Therefore, they may serve as pathogen-free scions for propagation of ramets of resistant P. thunbergiiclones and construction of seed orchards in PWD non-epidemic locations.

AbstractParasitism by parasitoid wasps on the larvae of Epinotia granitalis(Butler), which is a wood-injuring pest in coniferous plantations, was observed for 6 years in two plantation forests of Chamaecyparis obtusa(Sieb. et Zucc.) Endl. and Cryptomeria japonica(L.f.) D. Don that were adjacent to each other and consisted of trees of almost the same size. E. granitalislarvae were collected from early April to mid-May, then reared in glass bottles, and finally examined to determine whether or not the larvae had been parasitized. Five species of parasitoids were recorded; two of them were classified in Ichneumonidae, Campoplexspp. A and B, and others in Braconidae, Iconella repletaPapp, Bassus cingulipesNees von Esenbeck, and Braconspp. In all 6 years, parasitism was first observed around 20 April. Species composition of parasitoids differed greatly among years and between forests. In 1 year in each forest the percentage parasitism increased significantly with the sampling date, indicating that not all parasitoids attack the same developmental stage of E. granitalis. The mean percentage parasitism per year was significantly higher in the forest of C. obtusa[11.5(%) ± 5.7(SD)] than in the forest of C. japonica(3.0 ± 4.1). These results suggest that the efficiency of parasitoid adults in finding hosts differed between the two forests.