Two new pyrrolizidine alkaloids, ideamines A and B, together with the known analogs lycopsamine and parsonsine, were isolated as N-oxide forms from adult bodies of the Apocynaceae-feeding danaine butterfly Idea leuconoe. Ideamine A was characterized as a homolog of lycopsamine, in which the viridifloric acid moiety was replaced by a 2-ethyl-2,3-dihydroxybutanoic moiety. Ideamine B was identified as a nor-derivative of parsonsine, in which the trachelanthic acid moiety was replaced by a 2-ethyl-2,3-dihydroxybutanoic moiety diastereomeric to the necic acid from ideamine A. The alkaloids were demonstrated to be acquired by larvae directly from the host plant Parsonsia laevigata, sequestered as N-oxides in both male and female adult tissues, and females could transfer portions of the alkaloids to eggs. Ideamine N-oxides (1 and 3) were homologs of lycopsamine and parsonsine N-oxides (2 and 4), respectively, lacking one carbon unit from the hydroxybutanoic moiety, with the necic acids in monoesters (1 and 2) being diastereomeric to those in cyclic esters (3 and 4).