Takeaways
- Cycads — tropical plants often mistaken for palms — offer a window into the origins of insect pollination. By studying the oldest lineage of insect-pollinated plants, Shayla Salzman is uncovering how early plants guided insect behavior long before flowers evolved.
- Ancient plants use heat, scent and humidity — not petals — to move pollen. Cycads manipulate specialized beetles and weevils using metabolic cues, revealing what may be the oldest pollination mechanisms still in operation.
- Understanding beneficial relationships between plants and insects supports conservation. Because cycads are the world’s most endangered plant order, deciphering how their pollination systems function could help protect both the plants and the insects that depend on them.
When most people picture pollinators, they imagine bees moving between bright, colorful flowers. Shayla Salzman studies pollination across deep time, focusing on insect behavior and the ways plants evolved to guide those behaviors long before flowers existed.
Salzman, a behavioral entomologist in the University of Georgia’s College of Agricultural and Environmental Sciences, studies cycads, the most endangered plant order in the world. She is drawn to them not simply because they are ancient plants, but because of the insects that depend on them. Cycads are the oldest existing lineage of insect-pollinated plants, and their survival hinges on tight, ancient partnerships with specialized beetles and weevils that have coevolved alongside them for millions of years.
“Anything we can learn about how cycads evolved insect pollination — how they manipulate insects to move pollen and achieve reproductive success — gives us insight into how plant–insect pollination began,” said Salzman, an assistant professor in the UGA Department of Entomology.
Metabolic cues, not flowers, guide beetle pollinators
Unlike flowering plants, which evolved vivid colors and visual signals to attract pollinators, cycads reproduce using woody cones with no showy displays. That absence of flowers is precisely what makes them valuable to Salzman’s work.
Cycads predate flowering plants by millions of years, meaning their pollinators likely evolved to respond to far simpler cues.
Instead of visual signals, cycads rely on a suite of metabolic cues like scent, temperature and humidity to manipulate insect behavior. Salzman has spent years disentangling how those signals work, including field research conducted as a Kelly Botanical Research Fellow at the Montgomery Botanical Center in Florida, a global conservation hub for cycads.
In earlier work, Salzman showed that cycads use a push-pull scent mechanism linked to thermogenesis, the ability to generate heat. By alternately attracting and repelling insects, cycads can precisely time pollination. The findings point to what may be the oldest pollination mechanism still operating today.
That work led Salzman to look beyond scent. In a study published last year, she demonstrated that the beetles and weevils that pollinate Zamia cycads use humidity as a key cue to locate host plants — a signal that she later found was strong enough to override their instinct to avoid unfamiliar plant odors.
More recently, Salzman contributed her expertise in insect behavior to a Science study led by Wendy Valencia Montoya, a longtime collaborator, which showed that heat itself also plays a role in guiding pollinators.
SCIENTIFIC AMERICAN
Before Flowers Existed, These Plants Lured Insects with Heat
“Organisms don’t rely on just one signal,” Salzman said. “Insects integrate whatever information they can detect. Right now, we’re studying each signal individually, and then we’ll start looking at how they function together.”
The system makes evolutionary sense, she said. Early insect-pollinated plants likely relied on basic metabolic cues — heat, moisture and gases — long before bright petals or complex scents evolved.
“Over time, that became purple flowers or vanilla-like scents,” Salzman said. “Cycads are ideal for studying this because they’re ancient, not showy and thermogenic.”
Ancient plant–insect relationships inform conservation
At the center of the system are Rhopalotria weevils and Pharaxanotha beetles. Every known member of these groups lives in close partnership with cycads. Adult insects gather on the cones to feed and mate, laying their eggs inside the cone tissue. The larvae grow and develop there before emerging as adults.
In other words, their entire life cycle is tied to the cone. The plants rely on the insects to carry pollen between male and female cones, and the insects rely on the plants for both food and a place to reproduce.
She said such tight mutualisms are often described as evolutionary dead ends — if one partner disappears, the other is unlikely to persist. That risk is especially relevant for cycads, which are now the most endangered plant order in the world.
But Salzman’s work suggests the relationship may be more flexible than once assumed. If insects can also rely on general cues like humidity and temperature rather than just highly specific signals, they may be better equipped to adapt if conditions change.
To test how broadly those signals apply, Salzman has begun studying southern magnolias, another ancient, thermogenic, beetle-pollinated lineage. Unlike cycads, magnolias produce flowers, making them a useful comparison for understanding which pollination cues have persisted across evolutionary time and why.
Beyond basic science, the work has practical implications. Understanding how cycads reproduce supports conservation efforts for a highly threatened group of plants and deepens scientific understanding of how plants and insects depend on and coevolve with one another.
Honestly,” Salzman said, “I just fell in love with these plants. There’s a quote I love from cycad biologist Knut Norstog, who said cycads are the Rosetta Stone of plant biology. But I’d extend that to say they should be considered the Rosetta Stone for understanding plant-insect interactions.”
Learn more about research out of the UGA entomology department at ent.uga.edu.
