Chemicals releasing oviposition by an Asclepiadaceae feeder, Ideopsis similis, were identified from a host plant, Tylophora tanakae. A strong positive response was evoked by a methanolic extract of the plant, which proved to contain multiple stimulants. A mixture of two phenanthroindolizidine alkaloids, (+)-isotylocrebrine and (-)-7-demethyltylophorine, isolated from organic fractions, elicited significant ovipositional responses from females.