Outwitting the Predators: Elizabeth Bernays and the Hectic Lives of Plant-Eating Insects.

Being a bug is a chancy thing. From the moment your egg is laid, you are the target of a vast array of predators hungry for your gushy, nutritive innards. Chances are, you will never make it out of your egg, as hosts of other insects either eat you directly or scoop you out to make room for their own babies to grow in the resources prepared by your mother. Out of a hundred eggs laid, it is a good day if a few dozen occupants make their way out, hopelessly, ludicrously exposed, their squishy, slow bodies ripe for the taking. Each stage after hatching is fraught with peril, and the odds are profoundly against a parent producing an offspring that makes it to maturity, even if they lay a thousand eggs. 

And yet, for all of that ninety-plus percent mortality rate of eggs and larvae, we still seem to have plenty of plant-eating insects around, and it is a fair question to ask, how? How is it that, century after century, and millennium after millennium, these creatures whose youth is spent under the constant and vigilant eye of a cavalcade of finely honed predators are still with us? Answering that question is a fascinating journey, and it turns out that the person who gave us our answers is one who, according to every piece of educational wisdom of her time, ought not have ever stepped foot in a university at all.

Elizabeth Bernays (1940-2024) was raised in the small town of Chinchilla, Queensland, the child of parents who were in a perpetual state of unease and tension. Her mother found some relief from the heavy sadness of her domestic life in the garden, and it was here that young Elizabeth well and truly lived. She was fascinated by growing and crawling things, and was content to spend hours out of doors, watching and collecting, a pastime she was encouraged in by a cousin of her close friend, who was a dedicated entomologist and provided young Elizabeth with not only the benefit of her wisdom, experience, and enthusiasm, but also the kit and techniques of the trade.

Her enthusiasm for nature and eagerness to learn the names and structures of the bugs she collected was a solace to her parents, a compensation for the absolutely dismal state of her grades. Her teachers’ unanimous opinion was that she was “slow”, and when asked about her hopes for the future, both they and the vocational professionals hired by her mother to test her aptitudes scoffed at the idea that she could ever be a university student, and should instead reconcile herself now to a life as either a wife or a worker drone of one stripe or another. 

They saw only her grades on the exams set before her, unaware of the time she has spent with the Queensland Naturalists’ Club, charming the adults around her with her curiosity and enthusiasm, or the notes she has received from the National Museum of Australia thanking her for sending them insect species previously unknown to them. Fortunately, in high school, she finally came across a teacher who recognized her gifts as a naturalist and encouraged them, taking time out of her own professional schedule to talk to young Elizabeth about the ideas of Charles Darwin, and the broader world of scientific inquiry. 

Elizabeth bloomed under this attention, and soon the girl who had been written off as uneducatable won a prize in her school’s science competition, and went on to win a scholarship to the University of Queensland, becoming the first person in her family to go to college. Here she enjoyed above all else her time with the Bushwalking Club, going on long rambles through the vast natural expanses of Australia. She graduated with honors in zoology and entomology, and after a year’s tour of Europe, she settled in England to teach high school, and eventually found her way to Birkbeck College for graduate work, where she came within the orbit of Reginald Chapman (1930-2003), a professor whose enthusiasm for entomological research was infectious, and whose informal scientific debate sessions at the local pub with his students was fondly remembered by all for decades after.

Bernays and Chapman were drawn to each other professionally, and soon personally as well. Though not attractive in the conventional sense, Chapman’s passion for his subject and broad joviality were magnetic, and it was not long before the two researchers formed a couple, one which would remain together, working side by side studying the things they both loved best, until Reginald’s death in 2003. 

Their joint studies would take them across the world, with much of their early career devoted to research of pest species which allowed developing nations to develop more effective strategies at protecting their agricultural output. One of their notable early successes came in their investigations of the mechanisms, both physical and chemical, that locusts use to determine when it is time to eat. It turned out that a number of concomitant factors contribute to a locust’s decision to start and stop eating. Bernays discovered the nerve in the digestive system that, if cut, caused locusts to continue shoving food into their mouths even if their whole body was backed up with food. She then traced that nerve to some glands which produced a hormone which, if injected into a locust, could stop it from feeding even if it had an empty stomach. But that wasn’t all - she found that locusts varied how much they ate based on the protein content of their food and that they possessed particular structures on the tips of their palps which closed when the locust was full, blocking off the locust’s ability to sense the nutrients around it, and pushing it towards the rest part of its feeding cycle. 

This was an elegant bit of research that put couple’s name firmly on the map of the entomological community, and laid out two roads before her - one, of travel to Nigeria, Mali, and India as part of various entomological task forces whose job was to determine best practices to protect plants from pests, and the other to a research career in the United States that challenged some of the foundational evolutionary ideas about how plants and insects adapted to each other over time. In the former capacity, she played a key role in developing procedures that interrupted the hatching cycle of devastating agricultural pests, and made discoveries about how certain strains of cereal crops contained chemicals that foiled the ability of larvae to orient themselves and successfully reach the location on the plant they needed to find in order to complete their life cycle. 

This was fascinating work, but if you know the name of Elizabeth Bernays today it is likely for her tritrophic theory. For decades, evolutionary botanists and entomologists had posited that plants and insects had been locked in an epoch-stretching dance that was the primary factor in driving each other’s evolutionary destinies. The plants, to avoid getting eaten, developed new chemicals that interrupted the life cycle or poisoned their pests, and the insects, in turn, developed ways of taking those new chemicals and turning them to their own advantage, developing tougher structures or resistances over time that tied them more strongly to their preferred food source, eventually becoming entirely specialized to that one type of plant. There were masses of data in support of this theory, including droves of insects who had incorporated previously lethal plant toxins into their own biochemistry as part of their own survival toolkit against other predators, but by the 1970s there was also a steadily growing stack of observations that spoke against the plant-insect dyad as the primary driver of both of their evolutionary histories. 

Bernays had, since childhood, devoted herself to closely observing the insect life all around her, and in her adult life that pattern continued, carrying her rigorous investigations from her fieldwork into the natural dramas of her own backyard. One day she observed a moth laying some eggs on a datura plant, and it occurred to her to make a study of the fate of those eggs. 210 were laid. Of those, 97 were devoured or repurposed as eggs for other species before they hatched. Of the 113 that were left and able to begin their lives as caterpillars, 24 reached the next stage of their growth, 7 made it to the third, 2 survived to become fourth-stage larvae, and 1 pushed onto the fifth stage, but was then parasitized in its pupal stage, meaning that the parent moth who had heroically given so much to produce 210 chances at life ended up with no progeny whatsoever. 

These were grim numbers, and they prodded Bernays to consider the subject further - with mortality being so high, with predation such a major factor, how could it not be a co-equal driving force of evolution alongside the insects’ struggles against the defences of their host plants. In the years to come she designed a series of ingenious experiments and carried out meticulous observations to see how a plant-eating insects’ relation to its host plant might be less about the actual chemical characteristics of that plant, and more about how it protected the insect from the far more immediate dangers of predators. 

She found that insects which specialized their lives around one particular plant experienced far less predation than those which generalized across several different species. Yes, the generalists had some advantages - by eating many different types of plants, they could gather many different types of chemicals that they could use in their defenses. But, it turned out in her studies, and those of other entomologists working on other species who corroborated her findings, the risks that generalists expose themselves to in carrying out their lifestyle more than outweigh the advantages of the extra defenses. The exposure to predators as they move between plants is perhaps the most evident of these, but there are other, more subtle forces at work. Almost all insects live on an Eat Fast, Retreat Fast strategy - munching insects produce motion, sounds, and scents that predators zero in on, so the winning plan is to get to your food, devour it, and get back to your hiding place as fast as possible. Specialists seem to do this better, because they don’t have to waste time deciding what they are going to eat, have special, efficient body structures to consume their target food, and don’t need to devote extra neural resources to the process, allowing them to get in and out faster, and be more vigilant while they eat, while generalists waste precious moments in decision-making, adapting their general jaw structures to the particular plant in front of them, and figuring out the best part to eat of each new plant, which often proves fatal. 

Tritrophic - three factors all mutually driving evolution - plants trying to avoid being eaten, predators seeking a meal, and nervous plant-eating bugs caught in the middle, trying to keep up with the plants so that they continue the specialist lifestyle which will give them optimum chances to live and reproduce in a predator-rich world. Bernays opened up a wider and more complex world of insect-plant interactions which proved a stepping stone to future researchers, who took her nuanced consideration of larger contexts and expanded it outwards, doing vast analyses of multitrophic evolutionary relationships that have as their ancestral figure that poor descendentless moth and the curious human who took its small dramatic life story as the starting point for a new conception of the complexities of our natural world.

Reg died in 2003, and in his death took with him a host of memories and shared discoveries, a loss that could have crushed Bernays’s zest for life and research, but she was able to find love again, meeting photojournalist Linda Hitchcock in 2004, and marrying her in 2018, while using her post-retirement years to create a whole new career for herself as a writer, authoring two treasured memoirs, Six Legs Walking: Notes from an Entomological Life (2019), and Across the Divide: The Strangest Love Affair (2023). 

Elizabeth Bernays passed away in 2024. Having never believed in gods or religion, finding meaning instead all around her in the desperate beauty of the creatures who completed their amazing life’s arc, full of transformation, peril, and new birth, in the space of a week, she considered her life a sufficient thing in and of itself, and there was no service to mark her passing or ascribe any comforting wider significance to the fact that one of the world’s most curious and keen minds had, after eight and a half decades, finally ceased in observing the world around her, and had begun the long process of returning to it.

FURTHER READING: Bernays is an entertaining writer, combining her clear love of her topic with a rare ability to make complex webs of relationships, chemical systems, and biological structures, crystal clear. Six Legs Walking is an absolute treat, as are her scientific papers and popular science articles. If you want to read something particularly wonderful, you can find her 2019 paper about Reginald’s life and their shared research work here.