Bugging Crickets

Scientists use tiny radio transmitters to study Mormon crickets' migration habits.

by / June 27, 2005 0
There are legions of them. Mormon crickets crawl. They leap. They destroy everything in their path. Nothing can halt the attack of these armored masses.

No, this isn't a B-grade sci-fi flick. It's not a biblical plague, although early Mormon settlers in Utah thought as much when hordes of Anabrus simplex Haldeman -- the scientific name for this two-inch, shield-backed, short-winged katydid -- descended on them in 1848, devouring their crops.

Desperate for salvation from the pestilence they believed God sent them, the settlers prayed to rid themselves of what they called "Mormon crickets." According to church legend, their prayers were answered when a flock of seagulls swooped down to feast on the insects.

If burgeoning populations of Mormon crickets in recent years are any indicator, ravenous bands could be poised to march across the western United States and Canada. Idaho, Utah, Colorado and Wyoming are typically hardest hit, spending millions of dollars to control the cricket migrations and the damage they do.

During a 1937 outbreak, crop damage amounted to $500,000 in Montana and $383,000 in Wyoming. In 2004, Congress made a special appropriation of $20 million for Mormon cricket control.

Three researchers are studying the crickets' migration by attaching tiny radio transmitters to them that chart their migration path. The goal is determining if better ways exist to stop the migration from hitting certain states, either through killing the crickets or diverting their migration path with concentrated and targeted pesticide application.

Containing the Swarm
"Little is known about what causes increases in population size," said Patrick Lorch of the University of North Carolina's biology department. "We know extended drought, early spring snow thaw and overgrazing all seem to favor high cricket densities. They lay eggs in the soil, and the eggs can sit for several years, hatching when conditions are most favorable."

Mormon crickets' culinary tastes lean toward succulent forbs, or broad-leaved flowering plants, but they'll graze on desert grasses before moving to greener pastures.

Insatiable, the insects engulf rangelands, laying waste to cultivated crops such as wheat, barley, alfalfa and clover. Experts say swarms of the crickets can cover a mile a day and eat everything in their path. Some packs stretch several miles wide and 10 miles long.

"A farmer might not see a single cricket one day but end up facing millions the next day because they move in such large groups," explained Gregory Sword, a USDA Northern Plains Agricultural Research Laboratory research ecologist in Sidney, Mont. "They can potentially eat everything in the field."

As unpredictable and destructive as a tornado, the ominous black band of crickets inexplicably shifts direction, decimating one field and sparing the next. In a moveable feast, the band can overrun communities, consuming ornamentals and stripping vegetable gardens bare. There have even been accounts of them chewing wood siding off homes.

In addition to the crop damage they do, the crickets also pose a threat to public safety.

"When their bands cross roads, they tend to mass together and cannibalize the crushed dead bodies of other insects," Sword elaborated. "These in turn get crushed by more passing vehicles, leading to large, messy 'oil slicks' of crushed crickets."

Until recently, when cricket bands were on the run, no one could predict where or how far they would travel. A study of Mormon crickets conducted by Lorch, Sword and Darryl Gwynne, a zoology professor at the University of Toronto, sheds new light on accurately tracking the Mormon cricket's migration habits. Together, these scientists devised a way to bug the pests that have been bugging humans for more than 2,000 years.

Tagging Crickets
Radio transmitters about the size of a dime and weighing 0.5 grams were hot-glued onto the backs of adult female crickets. Directed rearward on the insect, these tiny devices send signals detectable in brush or grass to a distance of 500 meters.

"We use an antenna and a receiver to hear the 'pings' sent out by the radios," Lorch said. "Each radio transmits at a different frequency, so we can follow many individuals at once. Using the directional antennas, we physically track down each cricket."

Tagged females were recaptured at intervals over 24 to 48 hours to estimate their position, then released again. "Trying to follow an individual in that band and finding out where 'Joe Cricket' is today or a few hours down the road would be impossible without some kind of radio device," said Gwynne, who began studying mating habits of the katydids in the 1980s. "You can go back and get the same cricket every day, recover that cricket, and figure out where it is using GPS information."

Lorch said they will use a dual-processor G5 Macintosh when they begin running models. "We may find that parallel computers will be necessary," he said, adding that they don't have huge storage needs. "We hope that by learning more about Mormon crickets -- what motivates them, what directs them, etc. -- we will be able to help with control efforts. More generally, what we discover should help with other insect outbreaks, particularly ones that involve mass migration like African locusts."

Such migrations in underdeveloped countries cause widespread famine.

The Mormon crickets were studied in a series of three treatments, which included three replicates of six crickets each.

  • Treatment 1: Radio-tagged crickets were released into the band. Studies were done on how safety in numbers affects the survival of crickets in the band.
  • Treatment 2: Solitary tagged crickets were released where there was no band. Lone crickets do not form "selfish herds" and are lighter in color than their more gregarious dark-colored cousins, which amass in troops three miles deep and one mile across. Bands can travel up to 50 miles in a season.
  • Treatment 3: A tagged cricket was transported a short distance by vehicle then released back into the band. The crickets were relocated once a day for five days.

    Strong Defense
    "We recorded their position. We knew what direction they traveled and how they traveled," Gwynne explained. "I don't know if we can ever get to this point, but the information we're going to get is going to at least go toward understanding their direction movement and their distance movement as well."

    If you know where the band is going and when it might arrive, he said, you know where to drop the bait.

    "I'm anti-insecticide," Gwynne acknowledged, "but the most effective way of controlling these things is with bait. They just roll out sacks of poisoned food, the insects come along, eat it and die."

    The poison used to control crickets is not harmful to livestock.

    In Brazil, where residents prefer not to use chemical insecticides, which can contaminate milk and meat, there has been some success in controlling locust damage by introducing various parasites and pathogens.

    These methods haven't been used successfully to control Mormon crickets yet, according to Sword, but he said researchers at Utah State University are studying cricket diseases.

    The universal theme of those B-grade sci-fi flicks is that to effectively conquer the invader, you must first understand it. The same is true of Mormon crickets.

    "We hope the predictive movement models we produce will help farmers, ranchers, state, federal and other land managers by improving the efficiency of existing control measures, and reducing the amount of pesticide and manpower used to treat Mormon crickets," Sword said.

    "Our work in the United States understanding how and why Mormon cricket migratory bands form, as well as the ability to predict their movement patterns, can potentially provide insight into the management of migratory pests around the world."
    Sue Owens Wright Contributing Writer