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    Jerrold Meinwald, 91; studied creatures’ chemical signals

    Jerrold Meinwald, who conducted pathbreaking studies of how creatures use chemicals to attract mates, repel predators, and send other messages back and forth, died on April 23 at his home in Ithaca, N.Y. He was 91.

    His death was reported by Cornell University, where Dr. Meinwald had worked for more than 50 years.

    One project that Dr. Meinwald, an organic chemist, tackled soon after he arrived at Cornell in 1952 was determining what exactly in catnip drives some cats into a playful frenzy.

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    Dr. Meinwald isolated from the plant the active ingredient — a chemical called nepetalactone — and then deduced its structure.

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    He soon discovered an aspect of nepetalactone he had not known about. He was a giving a talk about his chemical findings, and someone had brought in a cat so he could demonstrate the effects.

    “It turns out not all cats respond,” Dr. Meinwald said in an interview in 2011. “I had a nonresponsive cat. The chemistry was good, but I had not realized you have to pick your subjects carefully.”

    Dr. Meinwald had a fruitful partnership with Thomas Eisner, an entomologist who joined the Cornell faculty in 1957. That collaboration continued for more than a half-century and established a new field of science, chemical ecology. Eisner died in 2011 at 81.

    Biologists had noted decades earlier that organisms produced substances that were not directly needed for the biological processes that maintain life. They suspected that these substances might be used for communications or defense. But it was only in the middle of the 20th century that chemists had the tools to study the substances in detail.

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    Eisner would typically note some intriguing behavior, usually involving insects. Dr. Meinwald would then isolate compounds and synthesize them in the laboratory so that Eisner could conduct experiments to confirm or disprove a hypothesis.

    “They got the ball rolling — it’s a vibrant field now,” May Berenbaum, head of the entomology department at the University of Illinois Urbana-Champaign, said in an interview.

    Consider whirligig beetles, which Eisner and Dr. Meinwald studied in the early 1970s.

    The beetles spend much of their lives swimming on the surface of water, seeming to offer nutritious, easy-to-catch morsels of food for fish and frogs. Eisner surmised that the beetles must have a way to make themselves less appetizing. He captured three species of whirligigs and then squeezed them with tweezers; the beetles excreted a white, milky liquid.

    “The next step was to isolate that substance, which is what Meinwald did,” said Roald Hoffmann, a longtime colleague of Dr. Meinwald’s in the Cornell chemistry department.

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    Dr. Meinwald identified a molecule called gyrinidal as a key compound in the secretions.

    After that discovery, more than a quarter-century passed before Dr. Meinwald and Eisner decided to return to the problem. Eisner now brushed synthetic gyrinidal produced by Dr. Meinwald onto mealworms and fed them to largemouth bass. The fish often spat them out.

    Another object of study was the mating behavior of tiger moths — “or what Jerry always used to call courtship,” Bruce Ganem, another Cornell chemistry professor, said. “He was a very proper sort of guy..”

    A female tiger moth emits a sex pheromone to attract males but would ignore males who lacked a certain chemical that repels predators, acquired by eating certain plants.

    During mating, the male transfers not only sperm but also a package of protective chemicals, which can equal 10 percent of its body weight. The female spreads the chemicals on the eggs she lays.

    “Isn’t that an incredible story?” Hoffmann said. “You can see that these stories are both simple and intricate. They are good stories. They’re good science, in a mixture of modern chemistry and good old-fashioned natural history.”

    Dr. Meinwald was born on Jan. 16, 1927, in New York City. After serving in the Navy as an electronics technician, he received a bachelor’s degree in chemistry from the University of Chicago in 1948 and a doctorate from Harvard in 1952.

    He then joined Cornell. Over his career, he was an author of more than 400 academic papers. He was a member of the National Academy of Sciences and the American Academy of Arts and Sciences. In 2014, he received the National Medal of Science, the highest honor that the United States government bestows for achievement in science and engineering.

    Dr. Meinwald was a founding research director of the International Center for Insect Physiology and Ecology in Nairobi.

    He is survived by his wife of 37 years, Charlotte Greenspan, and three daughters, Constance Chu Meinwald, Pamela Meinwald, and Julia Meinwald. His marriage to Yvonne Chu ended in divorce.

    Berenbaum said part of Dr. Meinwald’s success was that he was willing, on occasion, to conduct tedious routine analysis for the sake of a biology puzzle that Eisner had identified.

    She said Dr. Meinwald himself gave the example of their study of vinegaroons, desert arthropods that fire a highly acidic spray from a turretlike structure in their tails.

    The spray, Dr. Meinwald reported, is about 84 percent acetic acid. (Common vinegar is typically 5 percent acetic acid.)

    “A chemist can’t build a career on identifying acetic acid,” Berenbaum said.

    Mixed in was 5 percent caprylic acid, also not a complex molecule. But caprylic acid is an oily liquid that allows the poisonous spray to adhere and spread on enemies’ bodies more effectively.

    “These two chemicals by themselves are not chemically interesting,” Berenbaum said. “Together, they explain an awful lot about the behavior of a really intriguing kind of arthropod.”