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Pittosporum tobiraseedlings were inoculated with Fusarium solaniisolated from Scolytogenes birosimensis, a bark beetle that infects P. tobira.The fungus produced necrotic lesions in the phloem and a discolored zone in the sapwood. Seedlings inoculated with the fungus and grown under weak light conditions were killed within 12–30 days after inoculation. Isolates from both S. birosimensis, which has caused P. tobiradecline in Aichi and Fukuoka prefectures, and from the beetle under endemic conditions in Ibaraki Prefecture were both pathogenic to P. tobira.

AbstractTo clarify the effects of asynchronous seed production among tree species on the population of seed predators, we investigated the relationship between the annual variation in production of mature acorns and the insect damage in those acorns of two sympatric oak species, Quercus variabilisBlume and Quercus serrataThunb. ex Murray, over 4 years at two study sites. The annual variation in acorn production was noticeable, with a coefficient of variation (CV) at the two sites of 1.05 and 0.80 for Q. variabilisand 0.87 and 0.73 for Q. serrata. Annual fluctuation in acorn production by Q. serratawas synchronized between the two sites. Since annual fluctuation in acorn production was not synchronized between the two species, the CVs for the total acorn production by both oak species (0.83 and 0.62 at the two sites) were lower than those for Q. variabilisand Q. serrataalone. The rate of predation by the specialist predators (Curculioweevils) on the acorns of both species was not related to the annual acorn crop size. Prolonged diapause of Curculioweevils might stabilize their populations. The rate of acorn predation by the generalist predators (tortricid moths) was also not related to the annual crop size. Asynchronous acorn production by the two oak species would help to stabilize the population.

The dynamics of the fungal symbionts in the gallery system and the mycangia of the ambrosia beetle, Xylosandrus mutilatus, were studied in relation to its life history using both isolation experiments and scanning electron microscopy (SEM). In the galleries, Ambrosiellasp. was predominant during the larval stages but its relative dominance gradually decreased during the development of the larvae. In contrast, yeasts (mainly Candidasp.) and Paecilomycessp. dominated continuously in the galleries after eclosion. Ambrosiellasp. was consistently stored in the mycangia in all adult stages, except in the teneral and overwintering adults when the other fungi were dominant. No fungal spores occurred in the mycangia of the adult beetles reared under aseptic conditions from the pupal stage, while only Ambrosiellasp. was stored in those reared from the teneral‐adult stage. These results suggest that: (i) Xmutilatusis associated with at least three fungal species, among which Ambrosiellasp. is the most essential food resource for development of the broods; (ii) immediately after eclosion, new female adults may take at least four associated fungal species, with no or incomplete selection, into their mycangia from the walls of the cradles; and (iii) conditions may well be produced in the mycangia of both matured and dispersing beetles whereby only the spores of Ambrosiellasp. can proliferate.