The effects of carbon dioxide on milkweed (Asclepiadaceae) and monarch butterfly (Danaus plexippus) larva
This research evaluated the effects of ambient and elevated carbon dioxide treatments on the growth of two species of Asclepiadaceae (Milkweed) plants: Asclepias curassavica (tropical milkweed) and Asclepias tuberosa (butterfly milkweed) and the effects on Danaus plexippus (monarch butterfly) larva. Aboveground, belowground, total dry mass, number of leaves, chlorophyll content, leaf surface area, latex dry weight, and percent nitrogen was quantified. Danaus larva was monitored for feeding preference and 3rd instar weight, mean weight from 3rd to 5th instar, and length of pupation was measured. Asclepias curassavica showed significantly greater above-, belowground, total dry mass, height, leaf numbers, and surface leaf area under elevated carbon dioxide conditions than in ambient levels, with significant decrease in dry latex weight and total foliar cardenolide content. There was no significant difference in percent nitrogen or chlorophyll content. For Asclepias tuberosa the only significant differences seen for carbon dioxide treatments were increased height, leaf surface area, and decreased chlorophyll content under elevated carbon dioxide treatments. Danaus plexippus larva did show a significant feeding preference between species, preferring A. curassavica over A. tuberosa, but no significant preference between carbon dioxide treatments. When reared on plant tissue, 3rd instar weights were significantly higher for larva reared on A. curassavica over A. tuberosa. Mean larva weight from 3rd to 5th instars showed a significant decrease for those fed A. curassavica grown in elevated carbon dioxide as compared to those fed ambient tissue. There was no significant difference seen between species or carbon dioxide treatments for calculated relative growth rate or mean time from 3rd instar to pupation.