Annual fluctuation and seasonal falling pattern of mature acorns of the beech family and a survey of their acorn-infesting insect fauna on subtropical Okinawa Island

A survey of the number of fallen acorns from trees of three species in the beech family (Fagaceae; Lithocarpus edulis, Castanopsis sieboldii, Quercus miyagii) and the insects that eat these acorns was conducted on subtropical Okinawa Island between 2000 and 2005. The largest number of L. edulis acorns fell in 2001, whereas only a few acorns fell in 2005, and there was little annual variation in the other years. The acorn production of C. sieboldii was repeatedly synchronized and abundant, with large numbers of fallen acorns in 2000 and 2003. Although Q. miyagii produced large numbers of fallen acorns in 2000 and 2005, none were collected in 2002 and 2004. The years of maximum production of mature fallen acorns did not coincide among the three species during the 6-year study period. Eleven species of acorn-infesting insects were confirmed: five coleopterans, three lepidopterans, two hymenopterans, and one dipteran. Curculio hilgendorfi, Poecilips cardamomi, P. graniceps, and P. variabilis damaged acorns of all three tree species, whereas P. advena damaged only C. sieboldii and Q. miyagii acorns. Neoblastobasis biceratala damaged C. sieboldii and Q. miyagii acorns, but Camptomastyx sp. and Tortricidae (Olethreutinae) sp. damaged only those of C. sieboldii. Cynipidae sp. 1 damaged L. edulis and Cynipidae sp. 2 damaged Q. miyagii, whereas Tipulidae sp. damaged L. edulis and Q. miyagii. This study is the first to document the presence of P. cardamomi, P. graniceps, P. variabilis, and N. biceratala on Okinawa Island. Additionally, there are more species in the post-dispersal acorn-feeding guild (PAF guild) than in the mature acorn-feeding guild (MAF guild), and it is inferred that this guild difference represents a difference between subtropical Okinawa Island and the temperate zone.