Forests with different flora and vegetation types harbor different assemblages of flower visitors, and plant–pollinator interactions vary among forests. In monsoon‐dominated East and Southeast Asia, there is a characteristic gradient in climate along latitude, creating a broad spectrum of forest types with potentially diverse pollinator communities. To detect a geographical pattern of plant–pollinator interactions, we investigated flowering phenology and pollinator assemblages in the least‐studied forest type, i.e., tropical monsoon forest, in the Vientiane plain in Laos. Throughout the 5‐year study, we observed 171 plant species blooming and detected flower visitors on 145 species. Flowering occurred throughout the year, although the number of flowering plant species peaked at the end of dry season. The dominant canopy trees, including Dipterocarpaceae, bloomed annually, in contrast to the supra‐annual general flowering that occurs in Southeast Asian tropical rain forests. Among the 134 native plant species, 68 were pollinated by hymenopterans and others by lepidopterans, beetles, flies, or diverse insects. Among the observed bees, Xylocopa, megachilids, and honeybees mainly contributed to the pollination of canopy trees, whereas long‐tongued Amegilla bees pollinated diverse perennials with long corolla tubes. This is the first community‐level study of plant–pollinator interactions in an Asian tropical monsoon forest ecosystem.
The attelabid beetle Cycnotrachelus roelofsi constructs two types of leaf-rolls (cradles): one is suspended from leaves (suspended type), and the other is severed from the leaves (cut-off type). To evaluate differences in performance between these two cradle types, we monitored densities, survival rates, and mortality factors throughout the active season, from April to June. The proportions of the two cradle types changed over time; the suspended type was dominant early in the season but was gradually replaced by the cut-off type. Irrespective of differences in mortality factors between the two cradle types, the survival rate was always higher in the cut-off type than in the suspended type. Beetle mortality tended to be highest at the egg stage, and the predominant cause of mortality was parasitism by two minute trichogrammatid wasp species, Poropoea morimotoi and P. sp.1. Parasitism by P. morimotoi was significantly higher in cut-off cradles than in suspended cradles, when cut-off cradles were abundant, whereas parasitism by P. sp.1 tended to be higher in suspended cradles when suspended cradles were abundant. These results suggest opposed frequency-dependent attacks by P. morimotoi and P. sp.1. We discuss how these egg parasitoids maintain coexistence of these two cradle types.
Some phytophagous insects have been known to inoculate certain fungi on plant substrates. In many cases of such insect-fungi relationships it has been considered that fungi contribute to insects by decomposing lignin or polysaccharides, and that the insects feed on the decomposition products or fungi themselves. Females of the leaf-rolling weevil in the genus Euops (Attelabidae) store spores of symbiotic fungi in the mycangia and inoculate them on leaf rolls. To determine the effect of mycangial fungi on larval nutrition in E. lespedezae, the nutritional value was compared between leaves with and without mycangial fungi. Two Penicillium species were isolated from the mycangia. These mycangial fungi showed little effect on the decomposition of lignin and polysaccharides, and showed little effect on enhancement of soluble sugars within leaves. Thus, the mutualism between Euops and its mycangial fungi contrasts with the mainly nutritional mutualisms between wood-infesting insects (termites, bark/ambrosia beetles, and wood wasps) and lignin/polysaccharide-decomposing fungi.
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