Understanding Monarch Caterpillar Attraction to Butternut Squash

Monarch caterpillars (Danaus plexippus) are well-known for exclusively feeding on milkweed and turning down other plants. Because they only accept milkweed as a food source, they likely use chemical cues to identify this host. However, the feeding stimulants that monarchs respond to are unknown. Monarch caterpillars have recently been found to also eat butternut squash in artificial settings. The goal of this project was to gain a better understanding of why monarch caterpillars sometimes choose to eat butternut squash and how that food can affect their growth and survival, ultimately working towards identifying their feeding stimulants. This work included 1) examining growth and survival of caterpillars when given several types of squash to feed on compared to feeding on milkweed, 2) feeding preference between butternut squash and milkweed, and 3) potential feeding stimulants through painting butternut squash and milkweed extracts onto otherwise unpalatable leaves. Our results reveal that caterpillars can survive on butternut squash as 5th instars but that it dramatically slows their growth and they struggle to complete their life cycle. Monarchs fared far worse on butternut squash as neonates, despite the finding that neonate caterpillars were initially more attracted to butternut squash than to milkweed leaves and that second instar caterpillars were stimulated to feed when given butternut extracts on cabbage. Thus, butternut squash is both attractive and stimulates feeding, but does not contain sufficient nutritional value to support development. Future work will use this system to help identify the specific feeding stimulants for monarch caterpillars.

I am very grateful to have been able to work in the Agrawal lab. I had very little experience with both insect and plant research before this summer, and learning more about plant-insect interactions and the process of ecology research was fascinating. I gained experience both working in the lab and in the field, and I got to do work with both biological assays and observation based experiments. I was also able to learn about insect colony care and try out some chemistry techniques such as making bulk extractions and filtration during my project. This experience also helped me solidify what areas of biology I want to focus on in the future, as well as my plans around applying to grad school and potential careers.