Abstract
Flower visiting by butterflies for nectar feeding was studied quantitatively using the transect-counts method at a newly created riparian biotope located in Sakado, Saitama, central Japan. During the study period (May-November, 2003), 590 flower visits by 20 butterfly species were recorded. Although only 12 (34.3 %) of 35 nectar source plants were exotic plants, they received 74.2 % of the total flower visits. Dependency on exotics (the proportion of exotics to the total number of flower visits) varied seasonally and correlated negatively with the diversity of nectar sources which was determined by the Shannon-Weaner function. This trend implies that a few exotics are seasonally dominant (Erigeron annuus and E. philadelphicus in May-July, and Bidens pilosa and Solidago allissima in October-November). The comparison of the results of this study with those of a similar study conducted at Mt. Fuji, Japan, I suggest the possible use of the transect-counts of butterflies feeding nectar as a convenient method to quantify the prevalence of exotic plants.
