Pheromones are chemicals that are produced and released by animals. When they are released by an individual of a species, they affect the behaviour of other individuals. Animals secrete these pheromones to trigger different kinds of behaviour.

The pheromones that trigger sexual arousal can be thought of as a kind of ‘sex perfume,’ attracting other individuals of the same species. The researchers engineered plants to produce chemicals that mimic these pheromones

“Chemically synthesised insect pheromones are already used for pest control and have been for some decades. Some insect traps contain pheromones to attract the insects to them, for use in the house, garden, and in food production systems. Insect pheromones are considered as alternatives to broad-spectrum pesticides as they are highly species-specific and do not affect pollinators or other beneficial species,” said Nicola Patron, corresponding author of the research paper published in the Plant Biotechnical Journal.

Patron is a molecular and synthetic biologist working at the Earlham Institute in Norwich, England.

According to Patron, all such pheromone-based insect traps in the market are made using synthetic chemistry. But it is not possible to use such synthetic processes to make chemically complex pheromones, which limits their use. Also, the synthetic chemical processes could produce toxic waste during the manufacturing process.

There have been previous studies that documented plants and microbe cell cultures being able to produce these insect sex pheromones. So, the research team led by Patrol set out to create an alternative for the chemical synthesis of pheromones.

To create a chemical manufacturing process that is essentially powered by water and light through photosynthesis, the researchers turned to Nicotiana benthamiana, a species of tobacco. The same plant has been engineered to produce ebola antibodies and even coronavirus-like particles for use in covid vaccines. The same plant has previously been engineered to produce ebola antibodies and even coronavirus-like particles for use in Covid vaccines in the past.

They built new sequences of DNA in the lab that mimic moths’ genes and also put in place a few molecular switches that can precisely regulate how the molecules are formed. These switches can turn the manufacturing process on and off.

An important development in their research is that they found a way to finetune the production of these pheromones, as opposed to coercing plants to continuously build these molecules. The latter method comes with a few drawbacks.

According to Patron, increasing the efficiency of producing these chemicals diverts too much energy away from the plants’ normal growth and development. They may be able to produce large quantities of the pheromone, but it stops them from being able to grow large, which could reduce the overall manufacturing capability.

 The study looked at the pheromones produced by two moth species, including navel orangeworm and cotton bollworm moth pictured here. (Image credit: Earlham Institute)

While testing and refining the control of genes that are responsible for producing these molecules, the researchers found that they could use copper sulphate to tune the activation of genes, allowing them to control both the timing and activation of these genes. Copper sulphate is an especially great candidate for the job since it is cheap, readily available, and is already approved for use in agriculture.

Using copper sulphate, the researchers were able to carefully control the production of different pheromones and their components. They could then take this “perfume cocktail” to better suit specific moth species. This includes the navel orangeworm and cotton bollworm moths.

With this technology, plants can be converted into “green factories” that can produce these pheromones that can potentially be used instead of environmentally-intensive and harmful pesticides.

With the study, the researchers demonstrated that they can produce these molecules in plant cells. They also used analytical techniques to prove that these molecules are identical to the ones produced by moths. But they have not yet been tested on the insects yet. For that, they will need to extract the pheromones and use them in traps.

The researchers’ collaborators at the Universitat Politècnica de València in Spain are currently working on that. They will test the pheromones with caged insects to show that the plant-made pheromones can attract male moths just as well as chemcially-synthesised pheromones or even female moths.