Abundance and distribution of immature stages of the monarch butterfly, Danaus plexippus, on the food plant Asclepias syriaca were examined at a site in southeastern Wisconsin over one growing season. Estimated mortality for eggs and larvae was substantial (88%). Dispersal of larvae between individual food plants, along with egg and larval mortality factors, may result in low population density. Although the mechanism triggering larval dispersal is unknown, several alternative hypotheses are proposed for further examination.
Borkin, Susan Sullivan
"Notes on Shifting Distribution Patterns and Survival of Immature Danaus Plexippus (Lepidoptera: Danaidae) on the Food Plant Asclepias Syriaca,"
The Great Lakes Entomologist, vol 15
Available at: https://scholar.valpo.edu/tgle/vol15/iss3/11