Various population fluctuation patterns of light-attracted beetles in a tropical lowland dipterocarp forest in Sarawak

The population fluctuation pattern of light-attracted beetles was studied f rom August 1992 to September 1998 (for 73 months) using ultraviolet light-t raps set at. three vertical levels in a tropical lowland dipterocarp forest in Sarawak, Malaysia. During our study, a general flowering occurred from April to July in 1996, and flowering on a small scale in 1997 and 1998. We analyzed the data for eight scarabaeid and six meloid species, some of whic h were anthophilous species. Various fluctuation patterns were observed amo ng the beetle species in aspects of both seasonality and correlation with t he supraannual phenological pattern. Three large chafer species (Scarabaeid ae, Melolonthini) showed a clear seasonal fluctuation pattern with a peak o nce from March to May every year, the peak monthly catch greatly fluctuatin g annually. Other scarabaeid beetles did not show such a clear seasonal pop ulation pattern and hardly fluctuated annually. Populations of an anthophil ous scarabaeid species, Parastasia bimaculata, a specific pollinator of Hom alomena propinqua (Araceae), hardly fluctuated, probably because of its res ponse to the constant flowering of its floral hosts. Monthly catches of an anthophilous scarabaeid, Anomala sp., and meloid beetles showed clear supra annual patterns in response to the general flowering and were significantly correlated with the flowering intensity with or without a lag of a month. The fluctuation pattern of meloids suggests a supraannual population fluctu ation pattern of their hosts, i.e., megachilid/anthophorid bees.