Flowering Phenology and Anthophilous Insect Community in the Cool-Temperate Subalpine Forests and Meadows at Mt. Kushigata in the Central Part of Japan

We studied flowering phenology and anthophilous insect commumttes bimonthly in 1990-1991 in the primary cool-temperate subalpine forests and meadows at Mt. Kushigata, Yamanashi Prefecture, Japan. One hundred and fifty-one plant species of 41 families flowered sequentially from late May to mid September. A total of 2127 individuals of 370 species in eight orders of Insecta were collected. The most abundant order was Hymenoptera (35% of individuals) and followed by Diptera (33%), Coleoptera (28%) and Lepidoptera ( 4%). The number of species was highest in Diptera ( 47%) and followed by Hymenoptera (24% ), Coleoptera (18%) and Lepidoptera (9% ). The numbers of both species and individuals peaked in late July and early August. Bee fauna was composed of six families, nine genera and 34 species, lacking Xylocopinae and wild Apinae. The most abundant genus in bees was Bombus (76.7% of individuals) and followed by Lasioglossum (20.2%). Cluster analysis on flower-visiting insect order spectra separated 30 plant families into four groups: nine families (Geraniaceae, Elaeagnaceae, Onagraceae, Ericaceae, Labiatae, Scrophulariaceae, Campanulaceae, Liliaceae and Iridaceae) were visited mainly by Hymenoptera, one (Violaceae) by Lepidoptera, five (Celastraceae, Umbelliferae, Polemoniaceae, Dipsacaceae and Gramineae) by Coleoptera and 15 by Diptera and/or various orders. Cluster analysis on flower-visiting insect order spectra of 91 plant species separated them into five flower guilds: hymenopterous (36 plant species), dipterous (30 spp.), coleopterous (14 spp.), lepidopterous (two spp.) and general flowers (nine spp.). Significant correlations were detected between violet flower color and hymenopterous flowers and between tubular corolla and hymenopterous flowers. Seventy-three % of hymenopterous flowers and 93% of dipterous flowers were visited by bumblebees and hoverflies, respectively. Cluster analysis on flower-visiting bumblebee species spectra separated 42 plant species into five flower guilds: longest-tongued bumblebee flowers (eight spp.), B. honshuensis flowers (eight spp.), B. ardens flowers (three spp.), B. beaticola flowers (15 spp.), B. hypocrita flowers (eight spp.). The number of coflowering plant species within each flower guild was usually kept less than five and, at most, eight in B. beaticola flowers which sometimes shared a few bumblebee species. Flower-visiting patterns of anthophilous insects were compared among insect orders, families and bumblebee species. The most preferred plant family was Compositae in Hymenoptera, Diptera and Lepidoptera, and Saxifragaceae in Coleoptera. Niche segregation as to floral host utilization was detected among six bumblebee species, although there were overlaps. The two longest-tongued bumblebee species visited similar plant species, but the second longest-tongued B. diversus, was largely expelled from the flowers of the same guild by the longest-tongued B. consobrinus, and the flower-visiting pattern of B. diversus was rather similar to the third longest-tongued B. honshuensis. The high bumblebee species diversity and niche segregation among them are thought to be a reason of high species diversity of herbaceous plants at cool-temperate subalpine forests and meadows.