Selection of age classes of Sasa leaves by caterpillars of the skipper butterfly Thoressa varia using albo-margination of overwintered leaves

摘要

A blade of the bamboo grass Sasa veitchii var. hirsuta (Koidzumi) typically has a lifespan of 2–4 years. After winter, the edge of the blade dies and a white margin is drawn on the blade. Such an albo-marginated blade is thought to be of relatively low quality as food for insects. Caterpillars of the skipper butterfly Thoressa varia (Murray) (Lepidoptera: Hesperiidae) that fed on blades of S. veitchii almost always utilized current-year blades. The mechanism by which they discriminate between age classes of blades was studied. The caterpillars did not choose albo-marginated blades, but they chose overwintered blades whose margins had been removed. This indicates that they use albo-margination as evidence of the age of a blade.