Evaluation of different environments on monarch success in the context of seasonal plasticity in migration physiology

Over several decades, monarch butterfly migratory populations have declined from loss of overwintering habitat in Mexico, breeding habitat in the U.S., exposure to pesticides, and climate change. Non-migratory summer monarchs differ from fall migratory monarchs in physiology and behavior. Differences in response to environmental stressors between these populations has not been studied and investigating these responses to environmental stressors is fundamental to developing conservation strategies. This research investigated survival, development, and performance of monarchs reared in prairie and urban habitats under summer conditions to identify environmental stressors encountered by monarch caterpillars in the U.S. Midwest. Second instar monarchs from a laboratory colony were placed on milkweed plants in three prairie and three urban habitats. Development and survival was recorded daily until adulthood. For each site, milkweed leaves were collected for identification and quantification of pesticide residues and temperature and humidity was recorded every 30 minutes. Overall survival to adulthood was 24%, but prairie sites had a higher survival at 35% and urban sites at 13%. Adult traits including wingspan, metabolic rate, and egg count were measured to represent important parameters for migration and population growth. Recorded parameters will be correlated with environmental conditions and pesticide content in milkweeds; aiming to identify stressors to be evaluated in further laboratory studies. Based on methods developed in 2022, the experiment will be repeated in 2023 to compare caterpillars raised under summer and fall conditions. This work represents one of the first studies evaluating differences between non-migratory and migratory monarchs' responses to different environments.