In plants, processes from flowering to seed maturation are influenced by various factors, including weather conditions, resource supply, and damage inflicted by seed predators, that collectively contribute to annual variability in seed production. To identify the important factors associated with sound acorn production in Quercus serrata, from 2014 to 2020, we investigated the demographic processes from flowering to acorn maturation in six individual trees within a stand in a warm‐temperate secondary forest in western Japan. We found that the annual production of female flowers was positively correlated with the difference in April temperatures between successive years. However, their fluctuation was low and unaffected by either seed or flower production in the previous year. Compared with those of female flowers, the annual variability in sound acorn production within an individual was significantly higher and more synchronized. Key factor analyses revealed that reproductive losses due to the oviposition and sap‐sucking activities of Mechoris ursulus were the most prominent factors contributing to the observed annual variation in total predispersal losses at an individual level, and their effects were synchronized among individuals within a population. Survival from female flowering to sound acorn maturation was strongly predicted by the temperature in June, which corresponds to the period of adult M. ursulus emergence. Our findings indicate that the damage inflicted by the main seed predator during the predispersal stage can sufficiently regulate the sound acorn production patterns in Q. serrata that appear to resemble masting behavior (the highly variable and synchronized production of acorns within individuals).

Highly variable and synchronous seed production within a population (‘masting’) could be from either synchronised high annual variability in floral initiation (‘flower masting’) or synchronised floral abortion until maturity (‘fruit maturation masting’). We investigated the demographic processes of the female organs from flowering to seed maturity, including each type of insect damage identified, in Quercus serrata in six individuals within a stand from 2014 to 2020, western Japan. Although the annual production of sound acorns was significantly correlated with that of female flowers, the annual variability in sound acorn production within an individual was significantly higher and their synchrony increased, compared to those of female flowers. The annual production of female flowers was positively correlated with the temperature difference in April between the previous and flowering years. However, their fluctuation was low, which was neither affected by seed and flower production in the previous year nor contributed to predator starvation. Key-factor analyses revealed that reproductive loss due to oviposition and sap suction by Mechoris ursulus , a generalist seed predator weevil for oak species, was the largest and most important factor that contributed to the annual variation in the total pre-dispersal loss of Q. serrata . The survival rate from female flowers to sound acorns was strongly predicted by the temperature in June, corresponding to the emergence of adult M. ursulus . This study suggests that highly variable and synchronous sound seed production can be proximately regulated by seed predation when the main predator is a generalist.