Flowering phenology and anthophilous insect community at a threatened natural lowland marsh at Nakaikemi in Tsuruga, Japan

Abstract

Nakaikemi marsh, located in Fukui Prefecture, is one of only a few natural lowland marshlands left in western Japan, and harbors many endangered marsh plants and animals. Flowering phenology and anthophilous insect communities on 64 plant species of 35 families were studied in the marsh in 1994-95. A total of 936 individuals of 215 species in eight orders of Insecta were collected on flowers from mid April to mid October. The anthophilous insect community was characterized by dominance of Diptera (58 % of individuals) and relative paucity of Hymenoptera (26 %), Hemiptera (6 %), Lepidoptera (5 %), and Coleoptera (5 %). Syrphidae was the most abundant family and probably the most important pollination agents. Bee community was characterized by dominance of an aboveground nesting bee genus, Hylaeus (Colletidae), the most abundant species of which was a minute, rare little-recorded species. Cluster analysis on flower-visiting insect spectra grouped 64 plant species into seven clusters, which were respectively characterized by dominance of small or large bees (18 spp.), syrphid flies (13 spp.), Calyptrate and other flies (11 spp.), wasps and middle-sized bees (8 spp.), Lepidoptera (2 spp.), Coleoptera (1 sp.) and a mixture of these various insects (11 spp.). These flower guilds largely coincided with pollination guilds with some exceptions such as anemophilous grasses visited by specific syrphid flies. The flower-insect relationship in the marsh was discriminated from that in woodlands by rarity of specialized relationships and by prevalence of relationships between flowers and flies, most larvae of which grow in waterlogged habitats. Nakaikemi marsh is regarded as a rare, important wetland habitat not only harboring many endangered plant and anthophilous insect species but also fostering unique insect-flower relationships. The presence of some plant species originally pollinated by bumblebees nesting at forest floor suggests that the marshland should be conserved as a whole ecosystem uniting the marshland and the neighboring woodlands.