Solving the problem of wormy apples with pheromones

Meet the codling moth. Cydia pomonella - light brown speckled pretty mothly looking moth. Seems harmless, right? But codling moth larvae big problem. These wriggly pests burrow into fruit and eat it from the inside out. Whatever they don't eat rots. Totally wasted. So what's a farmer to do? Well, you can spray the entire orchard with pesticides, killing every bug in sight.

Or you can use the moth's own pheromones, those airborne sex molecules they use to find mates against them.

Female codling moths use pheromones so males can find them when it's time to mate. Then they lay their eggs on the leaf surface of fruit trees like apples and pears. When the larvae hatch, they find their way to the fruit and dig in, literally.

So tell me a little bit about why they're actually bad for crops.

The larvae as soon as it emerges from the eggs, it will get into the fruit and they will continue to feed.

They seal up the hole behind them with scraps of the fruit, so threads and frass, basically caterpillar poop. Disgusting.

To control these pests, you don't have to kill everyone. You only have to break the cycle. That's where pheromones come in.

Pheromones play a critical role in the life cycle of many animals, not just moths. These scented molecules use chemistry to relay messages about danger, food sources, and also sex. And that's where scientists found their solution to the old worm in an apple problem. About 30 years ago, they learned to make synthetic pheromones and use them to prevent the moths from mating.

You might be using them right now to catch moths in your closet. Stick some of these pheromones on a tree and every leaf and branch smells like a female moth. The males fly around in circles, mateless until they die.

Males cannot orient themselves towards one female or two females, because the smell is more powerful than the pheromone that's produced by individual female.

Because pheromones are species specific, other creatures in the orchard are left undisturbed and unharmed, but for this technology to work at scale, scientists had to overcome some challenges. First off, chemically synthesizing any species specific pheromones in the lab is complicated and expensive, requiring a long series of chemical reactions to get it just right. The solution to that problem involves using everybody's favorite fungus, yeast.

If you want to make a lot of some biological molecule, yeast is one of your go to options. You can introduce instructions in the form of DNA from other organisms into yeast pretty easily. We know which parts of the moth genome are responsible for making pheromones. So you can isolate those, add them into the yeast, and boom, you've got yourself a little biological factory. No assembly required.

Next, scientists wanted to find an easier way to distribute the pheromones. Up to this point, farmers have been using dispensers attached to individual trees. These are a lot of work to place and replace by hand. The scientists needed to create a sprayable version of their pheromones, one that would stay on the plant and not just evaporate or wash away as soon as it was released.

They decided to encapsulate the pheromones in a sticky, microscopic polymer shell that would release them over time. The micro capsules are formed by a process known as in-situ polymerization. First, the pheromones are blended into an emulsion with a monomer and other molecules that will make up the shell. When heated, the monomers polymerize surrounding the pheromones and forming the tiny spheres.

Then you add the ingredients that will make up the glue that will help the spheres stick to the plant. These spheres are designed to release the pheromones at a specific rate, depending on local conditions like temperature, moisture, and level of UV radiation from the sun. So it works kind of like an air freshener, which is great. But there's one more step.

Fine tuning the distribution system by tracking those local conditions in real time, because these moths are a moving target. They don't just meet once a year.

You know, you get these multiple generations throughout the season. So there is one generation in the larval stage that the adult mating habit is happening concurrently at the same time.

And you might only have a moth problem in a single spot.

Treating the whole orchard, which can be hundreds of acres, is just inefficient. So, the scientists combined at the sprayable pheromones with a series of remote sensors. Like small weather stations, these units track all kinds of data like temperature, rain patterns, and number of moths in an area. This data helps the farmer figure out the exact right time and place to spray the fields with more pheromones.

Walk into a grocery store in the U.S. or Europe right now, and you can pretty much bet that the apples, peaches, and grapes in that store were produced with the help of phony pheromones. And because of those sticky microspheres, we can now use pheromones to protect crops that don't grow on trees. Things like rice and corn that are too wet or have nowhere to hang a dispenser.

It's all an effort to waste less food, kill fewer good insects, and keep our food supply pesticide free. But you gotta feel a little bad for the poor moths who are just trying to get lucky.

Do you think about the work that you do when you walk into the produce section of a grocery store?

The most exciting part for me is learning how this technology can solve the problems in different parts of the world.