Terpenes are a diverse class of organic compounds found in many plants. They are responsible for the unique aromas and flavours of many fruits, vegetables, and herbs. They also play a number of important roles in plant defence, pollination, and communication.
The most common terpenes in plants include:
- Limonene: Citrusy, lemon-like fragrance
- Pinene: Piney, woody fragrance
- Myrcene: Earthy, musky fragrance
- Linalool: Floral, lavender-like fragrance
- Eugenol: Spicy, clove-like fragrance
- Geraniol: Rose-like fragrance
- Citral: Lemongrassy, citrusy fragrance
These terpenes are found in a wide variety of plants, including fruits, vegetables, herbs, and flowers. For example, limonene is found in citrus fruits, such as lemons, oranges, and grapefruit. Pinene is found in pine trees, rosemary, and basil. Myrcene is found in hops, cloves, and mango. Linalool is found in lavender, mint, and bergamot. Eugenol is found in cloves, cinnamon, and nutmeg. Geraniol is found in roses, geraniums, and palmarosa. Citral is found in lemongrass, lemon verbena, and balm.
Terpenes and Plant Defence
Terpenes can repel harmful insects in a number of ways – some are directly toxic to insects, while others act as deterrents. For example, limonene is toxic to aphids, while the pinene is a repellent for mosquitoes.
They can also interfere with the communication and navigation of insects. For example, myrcene can disrupt the pheromones that ants use to communicate with each other. This can make it difficult for ants to find food and their nests..
Research on the repellent effects on harmful insects
- A 2021 study published in the journal Plants found that limonene was effective in repelling aphids from citrus trees. The study found that limonene applied to the leaves of citrus trees reduced aphid populations by up to 90%.
- A 2022 study published in the journal Scientific Reports found that the terpene pinene was effective in repelling mosquitoes. The study found that pinene applied to the skin reduced mosquito bites by up to 70%.
- A 2023 study published in the journal Frontiers in Ecology and Evolution found that myrcene was effective in disrupting the communication of ants. The study found that myrcene applied to the ant trails disrupted the ants’ ability to find food and their nests.
Terpenes and Beneficial Insects
Terpenes can also attract beneficial insects, such as ladybugs, lacewings, and parasitic wasps. These insects prey on harmful insects, helping to control pest populations.
For example, the terpene linalool attracts ladybugs, which eat aphids and other small insects. The terpene eugenol attracts lacewings, which eat whiteflies and other soft-bodied insects.
On the other hand, some of these compounds can also attract beneficial insects, such as ladybugs, lacewings, and parasitic wasps. These insects prey on harmful insects, helping to control pest populations that may damage useful plants or crops.
For example, the terpene linalool attracts ladybugs, which eat aphids and other small insects. Eugenol attracts lacewings, which eat whiteflies and other soft-bodied insects.
Research on the attractant effects of terpenes on beneficial insects:
- A 2020 study published in the journal Biological Control found that linalool was effective in attracting ladybugs to aphid-infested crops. The study found that when linalool was applied to the crops, the number of ladybugs increased by up to 50%.
- A 2021 study published in the journal Pest Management Science found that the terpene eugenol was effective in attracting lacewings to whitefly-infested crops. The study found that eugenol applied to the crops increased the number of lacewings by up to 75%.
Terpenes and Pollination
Terpenes also play an important role in pollination. Pollinators, such as bees, butterflies and moths, are attracted to the bright colours and sweet aromas of flowers. Terpenes contribute to these aromas and make flowers more attractive to pollinators.
For example, the terpene geraniol is attractive to bees, while citral is attractive to butterflies.
Research on pollination:
- A 2022 study published in the journal Nature Communications found that geraniol was essential for the attraction of bees to flowers. The study found that bees could not detect flowers without geraniol.
- A 2023 study published in the journal Frontiers in Ecology and Evolution found that terpene citral was essential for the attraction of butterflies to flowers. The study found that butterflies could not detect flowers without citral.
Conclusion
Terpenes are important compounds that play a number of roles in plant defence, pollination, and communication. The can repel harmful insects, attract beneficial insects, and make plants more attractive to pollinators.
The compounds are also being investigated for their potential use as natural pesticides and insecticides. Some studies have shown that they can be effective in controlling a variety of pests, including aphids, whiteflies, and mosquitoes.
They also play a role in aromatherapy – some of the potential health benefits of essential oils seem to be derived from these compounds. For example: both linalool and myrcene have been shown to have calming and relaxing effects.
Research continues to explore terpenes in order to understand their therapeutic and medicinal potential.
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