Daytime Plant Smells Shape Butterfly and Moth Feeding Preferences

New research has proposed a chemical-based explanation for why some butterflies and moths are selective feeders while others are not. The study, published in Proceedings of the Royal Society B, introduces the "Salient Aroma Hypothesis", which suggests that variation in the timing and intensity of plant aromas influences the evolution of dietary specialization in Lepidoptera – a large order of insects that includes both butterflies and moths.

Daylight smells drive dietary specialization

The researchers conducted a meta-analysis of existing studies and found that plants release a greater diversity and quantity of volatile organic compounds during the day than at night. These compounds serve as chemical signals that help insects identify host plants. The team hypothesized that this abundance of chemical information available during daylight provides an advantage to day-active Lepidoptera, enabling them to specialize in feeding on a narrower range of host plants.

By contrast, moths that are active at night are exposed to fewer plant aromas. With limited sensory cues, these nocturnal species tend to have broader diets, feeding on a wider range of plants.

“This idea provides a new perspective on why some butterflies and moths are picky eaters while others are not,” said Dr. Po-An Lin.

Antennal size reflects reliance on smell

To explore how insects might have evolved to detect these scent cues, the researchers examined the size of the antennae – the primary olfactory organs – in 582 specimens across 94 Lepidoptera species. They found that females active during the day typically had larger antennae relative to body size than their nocturnal counterparts. Additionally, species with more specialized diets also tended to have larger antennae.

“The relationship between antennal size and host plant breadth was very strong,” said Dr. Gary Felton.

Larger antennae generally have a greater number of olfactory structures known as sensilla, which increases their surface area and enhances scent detection capabilities. This adaptation could be especially beneficial for females that must locate appropriate host plants on which to lay their eggs.

Linking sensory traits to evolutionary patterns

Using phylogenetic analyses, the researchers demonstrated a correlation between daily activity patterns and dietary specialization across the Lepidoptera family tree. This relationship supports the idea that plants, through their emission of volatile compounds, may have directly influenced the evolution of insect sensory systems and feeding behaviors.

The findings contribute to a broader understanding of how plant-insect interactions shape evolutionary pathways. According to the research team, including scientists from Penn State, the National Taiwan University and Harvard University, the Salient Aroma Hypothesis provides a framework for investigating the co-evolution of plant signals and insect sensory adaptations.

Reference: Lin PA, Chan WP, Cai L, et al. The Salient Aroma Hypothesis: host plant specialization is linked with plant volatile availability in Lepidoptera. Proc R Soc B. 2025;292(2042):20242426. doi: 10.1098/rspb.2024.2426

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