Intro: Terpenes are organic compounds found in various plants that play a significant role in insect control. These aromatic molecules act as natural insecticides, deterring pests and protecting crops without harming the environment. Terpenes are responsible for the distinct smells emitted by plants, which can repel insects or disrupt their feeding and reproductive patterns. Through their insecticidal properties, terpenes offer an eco-friendly alternative to synthetic pesticides, reducing the dependence on harmful chemicals in agriculture. Harnessing the power of terpenes in pest management promotes sustainable farming practices, protects biodiversity, and ensures a safer food supply for our society.
Terpenes can be found in essential oils of plants and are made up of small molecules produced by plants, including, fungi, insects, nematodes and bacteria.
It is talked wildly that chemical communication extends to humans and plants, especially when it comes to cannabis. Humans can receive communication through the scent of the plant, it tells us something about the plant and it makes us feel a special way.
Human olfactory receptors contain small depressions shaped to receive certain molecules. When those holes are filled with the correspondingly shaped volatile molecule the human brain perceives this as a smell. Therefore, we are built to integrate with terpenes. Our nose is sensitive enough to detect even small differences in the same terpene. Limonene is the best example of this, which is a top five terpene of cannabis. Limonene occurs as two different isomers, d-limonene and l-limonene. D isomer is perceived as citrusy, and 1 as fuel or pine.
Plants use terpenes as weapons of defense, to heal and protect wounds to promote propagation. They do this to protect the plants from fungi, bacteria etc. to communicate with other plants and organisms in their environment. Cannabis acts on the same and uses terpenes for similar purposes. Terpenes such as pinene, limonene, and linalool are considered the same from plant to plant they have many similarities and this how we can back up our evidence of them existing between plant species.
Insect traps/ repellents:
One of the most effective ways to manage pests is to physically immobilize them. Cannabis plants do this by producing large amounts of sticky trichomes containing terpenes like pinene and myrcene. These trichomes are produced and meant to act as a dangerous trap meant to immobilize the insects and or kill them. Pest companies and people have learned to use terpenes as insect repellents by studying its purpose. Pest repellents such as citronella or “OFF” mosquito repellent would be a prime example of how modern society uses the benefits of terpenes and created an insect repellent to help fight off and kill unwanted pests.
Plants can also produce terpenes that attack insects and act as a pesticide. Limonene, pinene, cineole, linalool, myrcene, and pulegone (common terpenes in cannabis) have all been shown to have fume like properties. Other terpene pesticides and other plants include caryophyllene, myrcene, and pinene have all been shown to be toxic to mosquitos, houseflies, aphids, and tobacco cutworms.
Some terpenes are made to attract plant pollinators like bees, wasps etc. Found in the essential oils of cannabis and other plants, they are strong aromatic molecules. For example, insects that are attracted to terpenes like limonene, will likely land on cannabis and are likely found in abundance. Pollinators that transport pollen from lemon flowers would explore cannabis flowers as they have high concentrations of limonene. Aromatic terpenes help to lure beneficial pollinators through scents. Terpenes like farnesene, ocimene, and myrcene are just a few examples of aromatic molecules that attract pollinators.
Predators and indirect defense:
Indirect defense is between the plant and the terpenes, making the terpene the defender. The plant uses the terpene to attract the predator. For example, when plants release a large number of variations of the terpene caryophyllene in response to insect larvae this attracts nematodes that prey on the larvae.
Defense against competitors:
When plants are competing for the same resources, terpenes can help to influence their growth. This can be done by releasing terpenes into the atmosphere. This process is called allelopathy, and terpenes and other chemicals involved are allelochemicals.
Two plants that influence the growth of cohabitant plant species marigold from South America, and the sage bush from Southern California. The marigold plant uses a variation of the terpene ocimene to prevent germination of other plants. These plants (mostly sage bush) release a terp blend of cineole and camphor into the air, which inhibits the germination of the seeds of other plants. **Growing tip: add spider mites to your garden because spider mites are attracted to marigolds. The scent, and the ease of the leaves will attract them to the marigolds, rather than your cannabis plants.
Some terpenes can also delay the growth in insect eggs, or larvae the same way they inhibit the development in plant species. Terpenes that can inhibit these factors include: limonene, linalool, geraniol, terpineol, pinene, cineole, merolidol, and variations of caryophyllene, which are all terpenes that occur in cannabis.
Defense against fungi and bacteria:
Variations of cineole, cymene, limonene, linalool, pinene, terpinene, and terpinolene, have all been found to possess antifungal activity. These are the top terpenes most commonly found in cannabis, making terpenes work effectively against bacteria.
When do plants produce and use terpenes?
Plant terpene production occurs at higher temperatures usually when the sun is shinning, and terpenes will evaporate as the daytime temperature rises. If you grow your plants outside for example, you probably notice a more potent smell in the morning. This is because the terpenes in your plants haven’t started to evaporate off yet, leaving the terpenes more potent. Experienced cannabis cultivars recommend harvesting plants in the morning.