“Sexy plants” are on the way to replacing many harmful pesticides, scientists say, by producing the sex pheromones of insects which then frustrate pests’ attempts to mate.

Scientists have already genetically engineered a plant to produce the sex pheromones of moths and are now optimising that, as well as working on new pheromones such as those of the mealybugs that plague citrus growers.

Sex pheromones are already used to protect some higher-value crops, such as tomatoes and berries. But the complex molecules are currently produced by chemical synthesis, which is expensive.

The new work uses a plant as a bio-factory, powered by the sun. Other researchers are also working on brewing sex pheromones using genetically modified yeast, a process already widely used to make, for example, insulin for diabetic patients.

Existing pesticides often harm both pests and beneficial insects, such as bees. Some are now pervasive in the environment around the world and are partly to blame for crashing insect populations. The world’s most widely used insecticides, neonicotinoids, were banned from outdoor use by the European Union in April. In contrast, pheromones are specific to each species and, being used in tiny amounts in fields, do not contaminate the wider area.  

Kinder to environment

“For many species, pheromone manufacturing is difficult and expensive,” said Nicola Patron, at the Earlham Institute, UK, which has received three years of European funding for the new project , along with scientists in Spain, Germany and Slovenia. “Bioengineering can provide viable alternatives to manufacturing, expanding the use of pheromones that will be much kinder to our environment.”

A pilot project called SexyPlant created a genetically modified tobacco plant that produces and releases the sex pheromones of the cotton bollworm and navel orangeworm, both larvae of moths. This is now being improved to give bigger yields. The same plant has already been engineered by others to produce ebola antibodies and polio vaccine.

In the new work, the pheromone will first be harvested from the plant and put in traps or dispensers to prevent pests mating. But in future, plants producing the pheromones could be planted alongside the crops they protect. This will prevent females finding mates and laying their eggs on crops, which the larvae then destroy, but will not affect the insects away from the field.

Patron and her colleagues are also isolating pheromones from citrus mealybugs, chosen because they are particularly complex molecules. “If we can do these, we can probably do most things,” said Patron.

She said crop plants were not themselves being engineered to produce pheromones, so no GM material would be in the final produce. Pheromones harvested from the plants could be used in fields quite soon, but putting pheromone-producing plants in fields is 10-15 years away, Patron said, because of the long regulatory process for GM plants.

Urgent need for solution

Other scientists, at the Technical University of Denmark (DTU), are exploring using engineered yeast cells to produce pheromones. “We aim to produce pheromones by fermentation and it will make the pheromones affordable for the protection of row crops, like maize and soybean,” said Irina Borodina at DTU.

One of the pests her group is targeting is the fall armyworm, which poses a major threat to food security in Africa and elsewhere. “African farmers have tried to treat this pest with insecticides, but it has become resistant,” said Borodina. “So there is an urgent need for a solution because otherwise people will starve.”

Different approaches are welcomed by Patron, whose group is also exploring the potential of fungi to produce pheromones: “At this stage of biomanufacturing, there is not one perfect solution and it definitely makes sense we try it across different types of organisms and see what is going to work.”

Chris Hartfield, at the National Farmers’ Union in England, said: “Looking for alternative ways of effectively controlling the many crop pests farmers face is at the heart of the integrated pest management approach taken by farmers and growers. Using pheromones and other biopesticides, where available, is an important part of that approach.

“Farmers are in the job of producing safe, traceable and affordable food, so the critical thing for them is to have an effective crop protection toolbox available to combat pests today,” he said. “If they lose a pesticide from that toolbox, food production could be severely impacted if the effective alternative is several years away at the end of a research project.”

By Damian Carrington, environment editor