Oviposition-stimulatory activity of phenanthroindolizidine alkaloids of host-plant origin to a danaid butterfly, Ideopsis similis
2001
Honda, K. | Omura, H. | Hayashi, N. | Abe, F. | Yamauchi, T.
Oviposition response of Ideopsis similis (L.) (Lepidoptera: Danaidae) was examined for 12 phenanthroindolizidine alkaloids present in its host plant, Tylophora tanakae (Maxim.) (Asclepiadaceae). At least five alkaloids, i.e. (+)-isotylocrebrine (3,4,6,7-tetramethoxyphenanthroindolizidine; 1), (+)-3-demethylisotylocrebrine (3), (+)-isotylocrebrine N-oxide (5), (+)-6-demethyltylocrebrine (8) and (-)-7-demethyltylophorine (10), were found to individually stimulate oviposition by females. Of these, compounds 1,3 and 10 were regarded as key components most responsible for host recognition or preference. However, female egg-laying was much higher in response to a mixture of the five alkaloids. In two-choice bioassays, more eggs were deposited on samples comprising the five alkaloids than on samples consisting of a single alkaloid. This suggests strongly that host selection by the butterfly is mediated by the synergistic action of several phenanthroindolizidine alkaloids present in the host plant.
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