Plant Scents Drive Butterfly and Moth Diet Choices

By Blake Jackson

A study reveals that plant scents play a crucial role in the dietary habits and evolution of butterflies and moths, collectively known as Lepidoptera.

Researchers at Penn State and their international collaborators have proposed the Salient Aroma Hypothesis, which suggests that the daily cycles of plant aromas influence how specialized an insect's diet becomes.

The study, published in Proceedings of the Royal Society B, examined why some Lepidoptera species have very specific diets, while others are more generalist feeders.

"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.

To test this hypothesis, the researchers analyzed the antennae, the primary smelling organs, of 582 specimens from 94 Lepidoptera species. They found that day-active female Lepidoptera tend to have larger antennae relative to their body size compared to night-active females.

"Larger antennal sizes have been associated with a greater number of sensilla, the sensory structures involved in the sense of smell," explained Gary Felton, a co-author from Penn State.

The study also revealed that specialist female Lepidoptera often have larger antennae than generalist females, likely due to their need to detect specific plant aromas. "The relationship between antennal size and host plant breadth was very strong," Felton added.

Researchers conducted a meta-analysis of existing literature to confirm that plants release more diverse aromas during the day. They also analyzed the Lepidoptera family tree to study the relationship between insect activity patterns and host plant preferences.

"Our analyses showed a significant correlation between being active during the day or night and the diversity of host plant species that Lepidoptera consume," said Naomi Pierce, a co-author from Harvard University.

Day-active Lepidoptera, like monarch butterflies, have evolved to be picky eaters due to the abundance of plant aromas during the day.

Night-active species, like the Polyphemus Moth, have more generalized diets because of the limited availability of plant aromas at night. "This is a crucial decision because caterpillars depend entirely on the selected plant for survival," Lin said.

The findings highlight the significant role of plant scents in shaping insect-plant interactions and evolutionary adaptations.

Photo Credit: istock-herreid