Scent of a Beetle Could Save Orchards
SACRAMENTO, Calif. _ A breeze stirs the almond orchard as researchers fan out in the Central Valley dusk, flashlights pointed downward. Their footsteps crunch in the dry leaves. They listen for the telltale hiss and flutter of the 10-lined June beetle.
This is science at its most hands-on. It’s a four-year beetle quest that Walter Leal, the head of the University of California-Davis’ entomology department, passionately calls “a matter of honor.”
Leal cut short a trip to Paris in pursuit of the 10-lined June beetle. His wife jokes that their summer breaks are dominated by the seasonal flight of the insect named for the stripes that line its back.
No one imagined this scientific search would extend four years or more when Leal and fellow entomology professor Frank Zalom teamed up to isolate and synthesize the elusive mating scent of an insect that plagues almond orchards.
Had he known, said Zalom, “I don’t think I would have done it. Now I just can’t give up. … I keep thinking every beetle we get, maybe this is the one that brings us over the top.”
Zalom and Leal had been hunting beetles in a Manteca, Calif., almond orchard, past rows of healthy trees and isolated patches of dead stumps and barren branches.
The trees are being killed by grubs, an infant stage of the beetle whose underground feasts can turn almond roots into hollowed, canoe-like husks.
The 10-lined June beetle ruins only a small portion of California’s $2.3 billion almond industry. But once it gains a foothold, there’s no effective defense against it.
So Leal and Zalom, along with others they rope into beetle-collecting, are hoping to develop a chemical weapon against the pest by harnessing its mating scent to disrupt the beetles’ breeding habits.
Their tools include the weirdly bionic “electroantennogram,” a scent detector that relies on an antenna plucked from a male beetle. Their labs are stocked with equipment for sophisticated chemical analyses.
Yet this is a quest that relies on dogged field work.
The females must be collected, beetle after beetle, night after night, during the brief half-hour or so when they emerge from the safety of their underground lairs to mate. Researchers need so many because each female 10-lined June beetle produces just a trace of a powerful pheromone that summons a male.
Since the females can be hard to detect, beetle-gatherers pace through the orchards in a near crouch, looking for the zigzag flight of a male, then track him to his chosen sweetheart.
One recent evening, Leal and Zalom recruited 13 graduate students, research assistants and visitors to prowl the orchards.
Their flashlights made bobbing pools of light as they searched, pounced and sometimes stumbled into almond branches.
The crew plucked more than 50 hissing females from their liaisons that night, adding to the roughly 400 female beetles gathered since June.
The premise behind the hunt owes its origins to a 19th-century French naturalist who watched in astonishment when dozens of male peacock moths came floating in through his windows and doors toward a female moth he’d just seen emerge from her cocoon.
It turned out the female emitted a chemical signal or scent called a pheromone, used to convey messages between members of the same species.
“Chemical communication is arguably the most ancient form of communication among animals,” said John Hildebrand, a University of Arizona neurobiology professor who studies how the brain responds to such signals. “It’s very effective.”
Most of the 1,600-plus insect pheromones analyzed so far involve lusty scents, making them ideal for developing tools to reduce insect populations.
This involves simulating the chemical and spreading it over a wide area to confuse would-be suitors.
Yet Hildebrand said the fascinating power of these chemical signals, among mammals as well as insects, deserves study for its own sake, too.
“Terrestrial arthropods _ insects, mites, spiders _ are the most successful fauna on the planet,” Hildebrand said. “We want to understand how come they’re so successful, just to understand the planet.”
Few come better equipped to seek that understanding than Leal, a Brazilian who rose to prominence in Japan’s government research establishment before coming to the University of California-Davis.
“He’s a major international figure, partly due to the beautiful work he’s done” on the structure of proteins that bind to pheromones as they enter the receiving insect’s body, Hildebrand said. “He’s a remarkably energetic and passionate person about his work.”
The 10-lined June beetle is only one of the many lines of inquiry that fascinate Leal _ but this quest he cannot let go. Over the past four summers, his lab has assembled countless tiny vials, each the size of a pencil stub, filled with a solvent in which female beetles have been soaked.
The insects are immersed 24 hours after capture, at dusk, when pheromone output is presumed to be most powerful.
Each summer since 2004, Leal has probed this beetle juice to try to isolate the blend of chemicals that gives a female her compelling charm. But nature has not been generous. Insects need to produce enough pheromones to alert each other to food or sex or danger, but not so much that they announce their presence to any passing predator.
The female 10-lined June beetle makes so little of the chemical that for three summers running, Leal could not extract enough pheromone to isolate it.
That changed in June. Leal gambled every sample in his lab on a large, pooled analysis. He isolated the pheromone, and ran smack into the next puzzle: figuring out its chemical makeup.
“It’s making it more exciting, entertaining, challenging,” Leal said, dodging an almond branch as he spoke.
The dual challenge now is, first, identify all the chemical constituents of the beetle’s “come hither.” Next, reproduce it.
Once the pheromone can be synthesized and field-tested, almond growers could spread it throughout an orchard.
This approach is called mating disruption _ fill the air with such a cloud of pheromones that a befuddled male never makes contact with a mate.
No coupling, no grubs. Which is a promising, if unromantic, way to make the world a little safer for almond orchards.
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(c) 2007, The Sacramento Bee (Sacramento, Calif.).
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PHOTOS (from MCT Photo Service, 202-383-6099): SCI-JUNEBUG
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