Carnivorous plants can attract insects with smell

Carnivorous plants come in a variety of shapes and colors – and often their appearance helps them attract their prey. However, these floral tricksters may use a different scene to attract their dinner: smell. A small study published this month in the journal PLoS One found evidence that different species Saraceniagenus of North American pitcher plant, produces scents that target specific prey groups.

[Related: Two newly discovered Andes Mountain plant species have an appetite for insects.]

Saracenia Pitcher plants typically make their home in swamps and in poor soil throughout North America. Their distinctive purple or reddish flowers are actually leaves that form a cup called a “jug” filled with digestive enzymes. If an insect gets too close to the plant, the pitcher traps it and digests it to supplement their diet in a nutrient-poor home.

The smell of carnivorous plants is not well studied by humans, but it has been suspected for more than a century. Charles Darwin wrote about the unique plants about 150 years ago, but concrete evidence of their olfactory mechanisms has been harder to find.

“Of the signals involved in communication, smell is perhaps the most enigmatic for humans,” co-author and carnivorous plant expert at the French National Center for Scientific Research Laurence Gaumé said in a statement. “In plants, it is often associated with other plant characteristics such as nectar, shape and visual cues, making it difficult to distinguish its effect from others.”

In this new study, a team identified the odor molecules emitted by four species of pitcher plants. The aromas seem to correlate with the types of incense that are rolled inside the pitchers. The chemicals that make up some of the scents are similar to those known to act as signals for certain insects, which could mean that pitcher plants have evolved to take advantage of their prey’s senses.

“It offers potentially interesting avenues in the field of biological control, and one could imagine drawing inspiration from the olfactory cues of these plants to control plant pests, for example,” Gaume said.

The team has grown Sarracenia purpurea and three of his hybrids with other plants in a pitcher in a laboratory.

They found that all pitcher plants produce a scent that is similar to more general plants that are pollinated by many different species. This may allow them to cast a wide net for prey, but they noted that there are subtle differences in the volatile organic compounds they produce.

[Related: Dying plants are ‘screaming’ at you.]

The pitchers, which attracted butterflies and bees, were rich in compounds such as limonene, a chemical that gives citrus fruits their unique smell. The scent comes from a class of chemicals found in the scents of about two-thirds of the flowering plants that attract these pollinators.

Meanwhile, S. purpurea also had an odor high in fatty acid chemicals known to attract parasitoid wasps and possibly other insect predators. Wasps and insects make up a large part of the plant’s diet, suggesting that the scent may be aimed directly at them.

The team found that both the scent of a pitcher plant and its size could help predict the prey caught by a plant about 98 percent of the time. This is not conclusive evidence, but suggests a possible link between the scent of the pitcher plant and its prey.

Since carnivorous plants cannot move to search for their prey like a lion or a shark, smells can help them not only to find food, but also to communicate with other plants. Plants that are eaten can emit scents that tell other nearby plants to prepare their defenses or produce a scent that attracts predators.

Plants that are pollinated by animals often rely on scents to attract pollinators, such as bees. Anything that masks their smell – such as air pollution – can cause a drop in the number of pollinators who can find them.

Additional studies could help explain how insect-pollinated carnivorous plants can attract some for pollination and others for food. For example, the most important pollinators of Venus flytraps are never inside the traps, and smell may play a role in this.

“However, we remain cautious as our results are currently based on correlations. Even with strong correlations, further tests are needed to investigate whether different insect species are indeed attracted to certain scents,” Gaume said.

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