Prolonged diapause of specialist seed-feeders makes predator satiation unstable in masting of Quercus crispula.

Quercus crispula (= Q. mongolica var. grosseserrata) is the predominant tree species in cool temperate, mixed broadleaf/conifer forests in northern Japan. We compared 11 years of data on acorn production in a population of Q. crispula, with data on seed-insect populations, to try to answer the following questions: (1) Does Q. crispula show a regular pattern of masting? (2) How long do principal seed predators remain in diapause? (3) How do the seed predators affect the pattern of predator satiation? Q. crispula showed a tendency to alternate bearing, with significant synchrony between individual trees. The principal acorn-feeding insects ( Curculio spp. weevils), which infested 25%-70% of matured acorns, generally exhibited a prolonged diapause of 2 years. No significant negative relationship was found between the rate of injury by the weevils and the density of mature acorns, indicating that simple predator satiation fails due to the synchrony of the life-cycle of acorn-feeding insects and the periodical production of acorns. However, the rate of injury by the weevils was negatively correlated with the relative abundance of mature acorns to the number of weevil larvae that had matured 2 years previously. Thus, the proportion of sound acorns notably increased in a rich crop after a disturbance in alternate bearing. Prolonged diapause of specific seed predators is critical in determining the peak year of sound-seed production.