Larval diet impacts flight performance in monarch butterflies

Few studies have described the effects of larval diet quality on adult insect flight performance. Flight muscle development and high-powered flight in insects are associated with costly energetic demands. Because larval diet is the energy source that powers these mechanisms, we asked whether larval diet has an impact on flight performance and metabolism in the monarch butterfly (Danaus plexippus Linnaeus).Monarch caterpillars from the eastern North American and Puerto Rican populations were fed a diet of either Asclepias incarnata L. (native to the eastern North American population) or Asclepias curassavica L. (native to the Puerto Rican population and uncommon in eastern North America). We flew the monarchs on a tethered flight mill to acquire flight performance metrics including velocity, distance, duration, power, and oxygen consumption rate.Monarchs reared on the A. incarnata L. milkweed showed slower, shorter, and less powerful flights than those fed on A. curassavica L. However, eastern North American and Puerto Rican monarchs, which were reared under summer conditions, did not differ in flight metrics or post-flight metabolic rates.The results suggest that flight in eastern North American and Puerto Rican monarchs is similar during the breeding season, yet the milkweed the caterpillars consume has important implications for flight performance.