The monarch butterfly, Danaus plexippus (L.), is a milkweed specialist that originated in the new world tropics and expanded its range into North America in the current interglacial period. Here, monarchs exploit a high diversity of native milkweeds in the genus Asclepias and show a complex migratory life history that facilitates annual milkweed exploitation over the entire spatial and temporal distribution of the plants. Since the 1840’s monarchs expanded their range to Pacific islands and reached Australia around 1870 where they exploit introduced milkweeds from South America, Africa and India. Such isolated island demes restricted to a limited number of host plants for 750-1000 generations, offers a valuable opportunity to test hypotheses on the evolution of insect host plant adaptations. We used monarchs and host plants from North America and Australia, in a transplant experiment, to test and compare survival and growth of first instar larvae. Experiments were run in the USA on A. curassavica, A. syriaca and A. eriocarpa and in Australia on A. curassavica, A. fruticosa and A. physocarpa. Generally the local monarch population performed “better” on local milkweeds compared to imports based on neonate survival and growth rate. Wing size and CG sequestration were more complex. We discuss these finding in relation to local host plant adaptations.