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Many organisms are acutely sensitive to the slightest whiff of chemical signals. These airborne messengers alter food chains and far more.
Beatrice Jin
Beatrice Jin

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Anurag Agrawal studies community interactions between multiple species, specifically insect herbivory on plants.
Frank DiMeo
Frank DiMeo

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Robert Raguso studies chemical communication between flowering plants and their pollinators.
Lindsay France (UPhoto)
Lindsay France (UPhoto)

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“I think what has allowed the group to synergize and push the envelope is the interlocking nature of our work,” says Agrawal. “Our research topics are highly overlapping.”
Frank DiMeo
Frank DiMeo

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Beatrice Jin
Beatrice Jin

Chemical Ecology—A Cornell Pioneered Field

by Lauren Cahoon Roberts

We live in a chemical world. Insects advertise their sexual availability. Plants sound a silent, smell-based alarm when they’re under attack. Flowers entice pollinators to probe their petals. While humans are mostly oblivious to their own pheromones and those of other living creatures, many organisms are acutely sensitive to the slightest whiff of these chemical signals. These airborne messengers can alter food chains and change the course of evolution. Yet, it was only in the 1960s at Cornell that these interactions were formally studied as a scientific discipline. This understanding of chemical interactions within and between species, and how they impact species abundance and diversity was dubbed “chemical ecology.” Since, interest and discoveries in the field have taken off around the world.

Today, the Cornell chemical ecology group continues to be a world leader and contribute to the body of research laid down by their mentors. “The collaborative work we do together crosses disciplines; it’s very integrative,” says Anurag A. Agrawal, Ecology and Evolutionary Biology, and one of the organizers of the group. “We are very fortunate to study what we study, it’s just great biology.”

The Founding Fathers

The founders of the field were a group of six Cornell faculty from diverse disciplines: Paul P. Feeny and Richard B. Root, Ecology and Evolutionary Biology; Thomas Eisner, Neurobiology and Behavior; Robert H. Whittaker, Ecology and Evolutionary Biology; Wendell L. Roelofs, Entomology; and Jerrold Meinwald, Chemistry and Chemical Biology. Together, they taught the first course on chemical ecology at Cornell in 1968.

A Collaborative Core

Fast-forward to 2003—Cornell made a major reinvestment in the field that it made famous and began an initiative to hire faculty who would specifically contribute to exploring the frontier of education and research in chemical ecology. Agrawal joined the team, in addition to six other scientists covering a broad range of scientific interests, with the community continuing to grow. “I think what has allowed the group to synergize and push the envelope is the interlocking nature of our work,” says Agrawal. “Our research topics are highly overlapping, yet leave enough room for professional development in novel areas.”

Agrawal studies community interactions between multiple species, with a focus on insect herbivory on plants. So does André Kessler, Ecology and Evolutionary Biology, but his research concentrates on how insect herbivory changes leaf and flower metabolism and morphology. Robert A. Raguso, Neurobiology and Behavior, studies chemical communication between flowering plants and their animal pollinators. Katja A. Poveda, Entomology, studies the agroecology of pests, using natural chemical signaling to reduce crop damage. Jennifer S. Thaler, Entomology, examines plant-herbivore-predator interactions with emphasis on physiology and behavior. George Jander, Boyce Thompson Institute for Plant Research, studies biochemical genetics, with a concentration on aphid herbivory. Michael Mazourek, Integrative Plant Science, breeds peppers and cucurbits to maximize flavor and pest control through the plants’ natural chemistry. Senior research associate Scott McArt in the entomology department studies both the ecology and evolution of plant-insects dynamics in agriculture and wildlands.

Long History, Broad Appeal

The chemical ecology group is not a formal institute. Instead, the integrative interests of the core faculty and their long-running consistency in meetings and collaborations bind and hold the group together. Every week 25 to 30 members of the group (the core faculty, along with many students and postdocs) get together for group meetings to discuss research and findings in the field.

Katja Poveda studies the agroecology of pests, using natural chemical signaling to reduce crop damage; and Jennifer Thaler examines plant-herbivore-predator interactions with emphasis on physiology and behavior.

The group is also distinguished by a course of the same name, taught by five faculty members who take turns giving lectures. About 75 students take the course each spring, from a diverse range of majors— plant sciences, neurobiology and behavior, entomology, ecology, and biology, as well as several majors from the colleges of Engineering, Human Ecology, and Arts and Sciences. “We’re very proud of our course’s broad appeal to a diverse student group;” says Agrawal, “and the course has been designated a ‘university course’ for the past three years, which has allowed us to add value in terms of demonstrations, field trips, and other forms of engaged learning.”

Scientific Synergy

In addition to teaching and meeting, the members of the chemical ecology group routinely collaborate on research. “Collaborative projects are published each year,” says Agrawal. “But that is the tip of the iceberg in terms of many informal interactions we have between labs—we have a very open-door policy. There’s lots of co-advising, lab equipment sharing, and hallway discussions that don’t make it into journal articles.”

The group also shares a core facility with a coupled liquid chromatography-mass spectrometry (LC-MS) instrument. This facility, supported by user fees and several campus units, has brought tremendous capabilities to a wide range of researchers. “Most prominently, the LC-MS facility has been critical in analyzing plant hormones, of which only a few orchestrate most of the plant’s functions,” says Agrawal.  

Aphid Alarm Signals

The published research brings together specialties of the different scientists. Jander and Raguso collaborated on a study that examined the pheromone response by aphids when they’re attacked by a predator. The pheromone, beta-farnesene, acts as a communal warning signal for the insects, which drop from the plant when they sense the chemical.

Certain plants release this warning pheromone as well. “Whether this farnesene production by the plants had evolved specifically to scare off aphids, or whether it has a separate function, was unclear,” says Agrawal. So, Jander genetically-modified plants that over-expressed beta-farnesene, and together with Raguso and their students examined aphid behavior when they fed on these modified plants. They found that the aphids changed—the insects no longer dropped to the ground when they sensed the alarm chemical, having become habituated to the beta-farnesene. At first glance, producing beta-farnesene didn’t seem to give much advantage to a plant—however, Jander and Raguso found that, when exposed to a constant dose of this pheromone, the insects were less responsive and wary of predators such as ladybugs--making them easier targets. The discovery created practical insight to the plant-aphid-predator interaction and opened the door to practical applications for pest control.

Mulling over Milkweed

Another collaboration within the chemical ecology group is centered on the research of Kessler and Agrawal. “Kessler’s group is very interested in the smells given off by plants and insects,” says Agrawal, “and at the time, my lab was focused on community interactions between many species.” Together, they investigated the interaction between the chemical composition of milkweed plants and their interaction with aphid pests. Some species of milkweeds easily repelled aphid pests, thanks to their chemical composition, while others didn’t. Agrawal’s group focused on documenting the pattern of these species’ community makeup to put it in an evolutionary context, while Kessler’s team provided the chemical expertise, finding the differences in the chemical volatile organic compounds that drove insects to be attracted to certain plants. “This illustrates one of the things that’s pretty special about our group,” says Agrawal. “Some people are engaged in applied work—identifying and isolating pheromones or arranging crops in a certain way to attract predators or repel pests. Other people are looking at the evolutionary causes behind the phenomena, such as why we have 140 species of milkweed in North America; others are more interested in the chemical basis of the interactions between species.”

For Agrawal’s forthcoming book Of Monarchs and Milkweeds (Princeton University Press), he presents a lavishly illustrated tome of significant scientific discoveries about monarch butterflies and their milkweed host plants and future sustainability. 

Moving Forward toward Biomedical Implications

Beyond the ecological, agricultural, and evolutionary implications of their research, the chemical ecology group is also moving toward biomedical work. Many of the chemical compounds the group studies are used to treat disease. “There’s a notion that if we understand the basic biology and chemical ecology, we can provide biomedical scientists with compounds that are highly active and potentially more effective.”

Fitting with their place in the establishment of the discipline, the Cornell chemical ecology group was asked by the Ecological Society of America to contribute a review of their field as part of the Society’s 100-year Anniversary issue. “We all met several times, and each of us produced a section, with Raguso taking the lead on writing and synthesizing the paper,” says Agrawal. The experience wasn’t without its bumps, however. “There was what I would call healthy tension during the process—we all had it out in a really great way. The experience allowed us to learn a lot about each other.” And the joint effort was worth it.  Their manuscript, which appeared in a 2015 issue of Ecology, came back with “the most flattering reviews any of us have ever gotten on a paper.”