This meeting and presentation took place entirely online via Zoom.
At 7:00 pm, Past President Ken Chaya called the Society meeting to order.
Ken made the following announcements:
- He welcomed all to the meeting.
- He welcomed the new members to the Linnaean Society:
- Amy Chai
- Catherine Crean
- Jordan Douglas
- Sheila Martin
- Maria Mercurio
- Judith Schechter
- Laurel Nadler
- Benjamin Smith
- Jeffrey Train
- Joe Zimmerman
- He invited all who are not members to join, explaining that membership information and directions for joining are on the Society’s website.
- The Tuesday morning spring migration walks in Central Park have begun. In addition to the Central Park walks, there are many other scheduled field trips. Ken invited everyone to visit the Society’s website for the listings and registration.
- The Great Gull Island birdathon is being held on May 10-11. It is a fundraiser event run by the Society in support of the study and protection of nesting Roseate and Common Tern colonies on this very special island. Information about participation in the birdathon is on the Society’s website.
At 7:03 pm, Ken turned to the lecture program and introduced the night’s speaker, Dr. Anurag Agrawal, James Perkins Professor of Environmental Studies at Cornell University in the Department of Ecology and Evolutionary Biology and the Department of Entomology.
Lecture: “Convergence and Divergence in the Diversity of Insects Feeding on a Toxic Plant,” presented by Dr. Anurag Agrawal
Tonight’s lecture was a captivating presentation on milkweeds, monarch butterflies, and the conservation of this iconic butterfly species.
Starting with a description of the monarch butterfly, Dr. Agrawal explained that like all members of the Lepidoptera (an order of winged insects that includes butterflies and moths), it goes through a two-stage transformation from the caterpillar stage (a “feeding machine”) to the butterfly stage (the adult, more mobile, mating phase). In addition, the vast majority of the monarch species undertake an extraordinary migratory journey from central Mexico to the northeast United States and southeast Canada, and back again. (Some population pockets elsewhere do not migrate). Using a circular graphical representation, Dr. Agrawal described the annual cycle of the monarch’s migration. As we are currently in April, he started with that point on the wheel. The monarchs have left their overwintering sites and are reaching the southern United States, where they mate and the females lay eggs, starting the first generation. Each generation goes through four life stages: 1) egg, 2) larva (caterpillar), 3) pupa (chrysalis), and 4) adult (butterfly). The butterflies of this first generation will continue to fly north, mating and laying eggs from which the next (second) generation begins. This process repeats for a total of three to four generations. With the exception of the final generation, the adult butterflies live for about one month. As the fall season approaches, the final generation, receiving environmental cues of shorter daylight, cooler nights, and dried milkweed leaves, will go into reproductive diapause. Their wings and wing muscles will be smaller than those of the previous generations, their reproductive organs will not develop, and their flight direction will turn south. Travelling at a rate of 30 to 50 miles per day over distances of 1,500 to 3,000 miles, they will reach their overwintering sites in forested mountains around 30 miles from Mexico City. They will spend the next eight months, fairly dormant, perched primarily on oyamel fir trees, at an elevation of 10,000 feet. Warmer temperatures and lengthening daylight cue them to begin their journey north, starting the cycle over again with a new first generation.
Dr. Agrawal explained that the only host plants of the monarchs are the milkweeds (genus Asclepias), and that milkweed and monarchs have coevolved. Milkweed has developed defenses with physical barriers such as trichomes (leaf hairs) that help protect the leaves from being eaten, and chemical toxins such as cardiac glycosides that are present in the latex of the plants. Monarchs have coevolved with genetics and strategies to overcome the physical barriers of the plant and to survive the toxic effects of the cardiac glycosides. Dr. Agrawal showed a photo of a monarch larva excavating a milkweed leaf to form a trichome-free area for feeding, and photos of examples of toxic-free zones where monarch larvae had chewed leaf veins, thereby stopping the toxic latex flow. That’s not to say that all monarch larvae survive this tactic—30 to 40% are poisoned and die—but the remaining ones not only survive the poison, they pack it away into their bodies and ultimately into their wings as a defense against their own predators. He gave the example of the Blue Jay, a bird that learns that eating a monarch will result in vomiting soon after—12 minutes, in fact—as reproducibly demonstrated in experiments by Lincoln Brower, a researcher well known for his work on monarch butterflies and his “barfing Blue Jays.” During the Q&A session we learned that there are other birds, however, that have adapted to successfully eat monarch butterflies, one being the Black-headed Grosbeak.
Dr. Agrawal devoted the final section of his talk to the conservation of monarch butterflies. He stated outright, “Folks, any way you slice it, monarch butterflies are declining,” and then he presented a chart showing census data of wintering monarchs in Mexico from the early 1990s to the present. The trend tracks downward until around 2015, after which it levels off, suggesting, at least for now, a stabilization of the population. Nevertheless, population decline is concerning, and understanding the reasons for the decline are critical to protecting the monarchs. Dr. Agrawal provided five lessons from his ongoing research and evaluation of the scientific literature:
- The importance of butterfly loss (disjunction) during the migration from the northern breeding regions to the overwintering ones is not fully understood. Habitat loss, lack of nectar plants, and lethal collisions with vehicles are among some of the possible factors.
- The monarch butterfly population fluctuates broadly and appears to be strongly influenced by regional climate from year-to-year.
- Parasites and predators play a large role in monarch populations and have links to their decline.
- Sublethal effects of pesticides, fungicides, and herbicides are impacting monarch populations.
- Planting native milkweeds has positive benefits, but data analysis has shown that milkweed availability is not a limiting factor, and this approach will not solve monarch population decline.
He emphasized that the decline of monarch butterflies is part of a much larger problem that is impacting many long distance migrating species.
Dr. Agrawal concluded by acknowledging the generous publicly-funded support that he has received through the National Science Foundation over the past twenty years. He noted that the National Science Foundation has been a critical fuel for the greatness of American science, and he hopes that it will continue.
At 7:51 pm, Vice President of Programming Karen Becker thanked Dr. Agrawal for an utterly fascinating talk. She then hosted the Q&A session, which covered many subjects, ranging from how the monarchs navigate to considerations about conservation, and more.
At the conclusion of the Q&A, Karen Becker thanked Dr. Agrawal again, and Ken Chaya returned to thank Dr. Agrawal for a wonderful talk. At 8:21 pm the meeting was adjourned.
Dr. Agrawal’s presentation and the Q&A session have been recorded in their entirety, along with Past President Ken Chaya’s opening meeting remarks. The recording is available for viewing on the Linnaean Society of New York website under the dropdown menu: Programs/Watch/ and on the Society’s YouTube channel, https://www.youtube.com/@linnaeanny/videos
Respectfully submitted by Lisa Kroop, Recording Secretary