Survival and Oviposition of Monarch Butterflies (Danaus Plexippus) on Invasive Pale Swallow-Wort (Cynanchum Rossicum) in Massachusetts
Abstract
Monarch butterflies (Danaus plexippus) have begun encountering swallow-wort (Cynanchum rossicum), an invasive plant in the milkweed family, in their summer habitat. There have been several reports of monarchs laying eggs on this novel host, but previous studies have found low levels of oviposition. These studies also found either low or no survival for larvae raised on swallow-wort. We studied monarch oviposition on swallow-wort using organisms collected in Massachusetts. We were also interested in whether the monarchs were responding to an oviposition stimulant in the swallow-wort or if they would respond to any substrate presented to them.
We found that, while monarchs laid significantly more eggs on milkweed than swallow-wort, they chose swallow-wort over species from other families (e.g., apple). In addition, we observed monarchs tapping their forelegs to test the quality of the host plant prior to oviposition on the swallow-wort, but not on the apple. Monarch performance on swallow-wort was poor with no individuals surviving to pupation. A significant number of larvae died during molting. We suggest that the foreleg tapping behavior and the preference for swallow-wort over apple indicates the potential for monarchs to incorporate it into their host preference hierarchy.
Description
Keywords
Monarch, Invasive Species, Milkweed, Swallow-wort, Danaus plexippus, Cynanchum rossicum, Asclepias syriaca