Scents of survival: How plant aromas shape insect diets

Every spring, gardens and fields fill the air with rich, floral aromas. But it’s more than just a pleasant smell; these plant-released scents play a vital role in the lives of butterflies and moths.

A new Penn State study reveals how daily changes in plant aromas influence feeding behaviors among winged insects that belong to the group known as Lepidoptera.

Plant scent and insect diets

The research, published in the journal Proceedings of the Royal Society B, unveils the Salient Aroma Hypothesis.

This new idea proposes that the chemical cues plants release – particularly during the daytime – are instrumental in shaping how specialized, or how flexible, a butterfly or moth becomes in its diet

“This idea provides a new perspective on why some butterflies and moths are picky eaters while others are not,” said Po-An Lin, an assistant professor at the National Taiwan University. “It also highlights the critical role of plant volatiles, or scents, in shaping insect-plant interactions and evolutionary adaptations.”

Picky eaters and their plant choice

Scientists already knew that many Lepidopterans are surprisingly fussy with their dietary choices.

The insects feed only on specific plant groups that cater to the nutritional or chemical needs of their offspring. Others are the polar opposite, feeding on a broad range of vegetation.

The hypothesis explains these extremes by focusing on how butterflies and moths use their antennae to detect plant scents.

Plant scent and insect antennae size

Researchers measured insect antennae on 582 specimens from 94 species and linked size to diet and activity patterns.

Notably, they found that day-active females in particular had noticeably larger antennae than their nocturnal relatives. This adaptation allows them to detect and process the richer daytime scents in the environment.

“The relationship between antennal size and host plant breadth was very strong,” Felton said. “Larger antennal sizes have been associated with a greater number of sensilla, the sensory structures involved in the sense of smell, thereby increasing the surface area for sensory receptors.”

“The enhanced capacity may be a key adaptation for how certain Lepidoptera have evolved to feed on a limited and specific range of plants.”

Chemical cues and evolution

The scientists confirmed that most vegetation releases a more varied and abundant blend of volatile compounds during the day, in comparison with the night.

This disparity lines up with the greater complexity observed in the olfactory systems of day-active insects. Daytime feeders use abundant daytime chemical cues to find, identify, and eat the plants that best suit their needs.

“This finding demonstrates how the availability of chemical signals influences the evolution of sensory organs in insects,” Felton said. “It provides a fascinating example of how plants have played a direct role in shaping the evolution of the insects that rely on them.”

The study also traced the evolutionary lineages of butterflies and moths in the Lepidoptera family tree. Researchers mapped species’ daily activity and linked it to host plant preferences to reveal feeding behavior.

Scent specialization in the daylight

The outcome is a nuanced picture of insect-plant dynamics. Daytime pollinators, like monarch butterflies, use their large antennae to detect specific plant scents, and this guides them toward a narrow range of host plants.

“Insect herbivores, such as butterflies and moths, must find the right plants to feed on and, in the case of females, to lay their eggs,” said Professor Lin. “This is a crucial decision because caterpillars depend entirely on the selected plant for survival.

In contrast, unlike humans, who eat a variety of foods to stay healthy, many insect herbivores specialize in just a few plant species.

Broader diets in the nighttime quiet

Nocturnal moths like the Polyphemus, encounter fewer distinct plant aromas in the dark. Without rich scent cues to guide them, these insects are less likely to lock in on a single preferred food source. Their evolutionary solution? Broaden their diet to improve their odds of survival.

By revealing how something as subtle as the timing and volume of plant odors can direct dietary choices, this study expands our understanding of ecological networks.

The research highlights the delicate interplay between insect sensory capabilities and plant chemistry, laying the groundwork for future research into how these relationships shape biodiversity across ecosystems.

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