1Hiroshima University, Higashihiroshima 739-8521, Japan.
2Fukuoka University, Fukuoka 814-0180, Japan.
Parantica sita is an oligophagous danaid butterfly that feeds on several asclepiads such as Marsdenia tomentosa and Tylophora tanakae. We examined plant chemicals present in M. tomentosa (Mt) that induce egg-laying by this butterfly. Females were bioassayed for their oviposition responses to artificial leaf surrogate painted with test materials (fractions from the MeOH extract of Mt foliage etc.). The activity was obtained from the aq. fraction, from which a number of cyclitols and related compounds were isolated. Of these, conduritol A (CA; major component) elicited moderate oviposition response, while conduritol F glucoside (CFg) evoked a stronger response, though it is a very minor component. Conduritol F (CF) was almost inactive in itself, however, it proved active when tested in combination with CA. From a series of experiments with a mixture of these compounds, the oviposition-stimulatory activity evoked by Mt was considered to be attributable to the synergistic effect of a large amount of CA and small amounts of CFg and CF.