Antelopehorn milkweed (Asclepias viridis) serves as both a nectar source and host plant for monarch butterflies (Danaus plexippus). Most plants flower in May and June and produce seed pods by late July. However, in areas burned during the summer, antelopehorn milkweed quickly recovers and flowers during August and September, encompassing the fall migration of monarch butterflies. The goal of this study was to evaluate the effect of summer burns on antelopehorn milkweed abundance and use by monarch butterflies. Our study area was located in north-central Oklahoma and included sites that had received a summer burn and unburned control sites. We collected data on antelopehorn milkweed nectar production, abundance, size, and flowering phenology, as well as the presence of monarchs and other insects on antelopehorn milkweed.
Results/Conclusions
Summer burned sites produced a surge in antelopehorn milkweed growth that was absent in unburned sites, where all plants had already gone to seed and senesced. Monarchs laid their eggs on the antelopehorn milkweed in these summer burned plots in September. The arrival of the monarch butterflies and the reproductive activities that occurred also support the idea of a potential premigration (i.e., a group of monarch butterflies that migrate before the normal migration period, which peaks approximately a month later). The timing of the arrival of the premigrants corresponded with the appropriate amount of time needed for any eggs that were laid to hatch, pupate, and join the peak monarch migration that followed approximately a month later. Thus, summer burns may provide a host plant corridor for premigrant monarchs, potentially making an important contribution to the overall monarch population.