The Last Word On Nothing

The moths arrived without warning. Thousands covered the walls and ceilings of the farmhouse where we lived one pandemic summer in northeastern Colorado. So many moths blanketed the spindly elm trees that they were indistinguishable from leaves until wind rattled them into flight. The trees appeared to slightly explode.

They were harmless miller moths, metamorphosed adults of the army cutworm, and native to the place. They were just passing through, really. After hatching underground on the high plains, the moths emerge and fly west each spring to drink the nectar of wildflowers in alpine meadows across the Rockies. Those that evade grizzly bears, which can eat tens of thousands of moths in a day, return to lay eggs on the plains in the fall. If only we’d been patient, the moths would have moved on of their own accord. We were impatient.

Hundreds of moths met the roaring maw of our vacuum. They came off the ceilings and the cabinets and the tables with satisfying little zips. Others we blasted with an air gun that shoots puffs of salt, which my girlfriend’s mom kept around for horseflies. Their soft brown bodies left oozing streaks on the walls. We placed pans of water and dish soap beneath reading lamps. The pans were filled with drowned moths by morning.

Indeed, the moths’ fascination with light had lured them into the farmhouse in the first place. Some moths use moonlight to orient themselves while flying; our farmhouse, surrounded by miles of empty beet fields, must have looked to the moths like a more attainable moon. We tried to exploit their light fixation to lure them out of the basement, where many had congregated, by holding a flashlight at the cellar door and jangling keys – we had read moths are alarmed by the high frequencies. Within minutes, a silent parade of moths appeared in the beam of the flashlight, flying towards the glow.

I remembered the miller moths a few weeks ago while working on a short piece about another, more sophisticated effort to annihilate and, in a sense, communicate with moths.

In addition to light (moon) and sound (keys), moths respond to scents. Many moths produce scents of such distinctive character that they only signal to moths of the same or closely related species. These scents are called pheromones, and for decades, farmers have used them to lure pest species away from crops. Some farmers deploy sex pheromone to lure male moths into traps; they fly to their deaths like sailors to sirens. Another method is to saturate fields with pheromones. Smelling love everywhere, the moths are unable to locate suitable mates. Populations crash within a generation.

Behind many of these pheromones is a Cornell chemist named Wendell Roelofs who set out in the 1980s to decipher the chemical signals of moths and other insects. Roelofs and his technicians extracted compounds from female moths and fed them into instruments to identify their chemistry. They puffed different fractions over male moths while electrodes attached to the antennae gauged responses. They released moths into miniature wind tunnels to fly along pheromone plumes. The process allowed the researchers to see how moths reacted to scents, identify the shape of pheromone molecules and their proper proportions, and, eventually, begin to make pheromones themselves. During his long career, Roelofs identified the pheromones of more than seventy species of insect, as well as the Asian elephant — which, incidentally, produces the same pheromone as the cabbage looper moth.

Roelofs and others after him had an environmentally friendly reason to go to all this effort hunting pheromones. Unlike conventional insecticides, which rain down death on a broad set of bugs, pheromones are a precision tool: they affect only their target species. Corn borers die while honeybees live. Targeted insects are also unlikely to develop resistance to pheromones, a regular occurrence with conventional insecticides. A moth with a mutation that made it unresponsive to its own sex pheromones would have little luck finding a mate.

Despite their promise, however, pheromones still aren’t as widely used as they might be. The global market for pheromones is but a sliver of the $300 billion market for insecticides.This is partly because pheromones are hard to identify and don’t work for every pest species. It’s also because pheromones are expensive to make, which limits their use to high-value crops like wine grapes, apples, and almonds. Lower-value staple crops like corn, soy, and rice are stuck with insecticide. To make pheromones cheaper, a group of academic and industry researchers are working on a method to produce pheromones in plants. They call the project “Grow Your Own Pheromone.”

To get a plant to produce an insect sex chemical, the group has inserted a gene from the diamondback moth into the oilseed plant camelina. The moth gene encodes an enzyme that alters fatty acids produced in the plant’s seeds to make them resemble molecules that a male diamondback moth would interpret as a female’s scent. The oilseeds can then be harvested and, with additional processing, yield pheromones. In recent field tests, the group reported significant progress. The pheromone produced using the bioengineered plants deterred moths as effectively as conventional pheromones. Yet the plant-based pheromone was much cheaper to make, perhaps even cheap enough to appeal to a soybean farmer. One of the project’s leaders told me their ultimate aim is to develop plants that dispense the pheromone themselves. Imagine smelling those flowers.

What strikes me about both these mothy encounters — at the Colorado farmhouse, and at the cutting edge of agricultural biotech — is how something that could have been used to communicate was first used to destroy. With lamps and flashlights, with keys, and with a suite of precisely refined molecular signals, messages were sent across hundreds of millions of years of evolution. We were communicating with flying worms! And all we had to say was “die.” Why did we default to killing the moths, and what possibilities for communication between species might we be missing?

In her essay The Death of the Moth — which, by delightful coincidence, I came across in an anthology on the shelves of the mothy farmhouse — Virginia Woolf observes a single moth perish on her windowsill. “One’s sympathies, of course, were all on the side of life,” she writes. That may have been true for her encounter with a single creature. But in infested homes and farms, such sympathies are not so accessible. Even Woolf only found the moth significant in its dying, and only then because dying is something humans also experience: “One could only watch the extraordinary efforts made by those tiny legs against an oncoming doom which could, had it chosen, have submerged an entire city, not merely a city, but masses of human beings;” she writes, “nothing, I knew had any chance against death.”

Nothing does. Least of all a moth navigating a world bright with artificial moons and fragrant with deadly scents. And we’re probably bound to some level of conflict with moths; a thousand insects in the kitchen is just not something you can ignore. But might there be other messages we could send before bringing out the vacuum — a polite signal showing them how to escape our glowing homes, perhaps? Or a pheromone lure, not to a trap, but to a meal that might help a group of traveling moths on their way? Are there dances with moths yet to be made? We have lights and molecules. They are on their way to drink from flowers in the mountains.

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James Dinneen is a writer from Colorado, now in New York, where he reports on all things environmental for New Scientist. Read more at jamesdinneen.wordpress.com

Photo Credit: James Dinneen