Grasshoppers' appetite is legendary. During severe infestations here in the United States, the voracious, fast-breeding insects can decimate grain and vegetable crops, and farmers dread them. But research entomologist Stefan Jaronski said American ranchers are the hardest hit when grasshopper populations rise.
Every year, swarms of the winged bugs routinely devour much of the available forage in the vast pasturelands of the western United States. "The primary impact of grasshoppers is as competition for cattle on rangeland. Much of the rangeland is marginal to begin with, and grasshoppers can consume up to 40 percent of the forage that's present, and then it becomes more difficult for the cattle to gain weight by pasturing," Mr. Jaronski said.
But dealing with insect pests on rangeland presents two significant problems. First, it's a vast territory to protect, so the cost of spreading pesticide can be prohibitive. Second, rangelands are complex and sensitive environments, meaning they are off-limits to many chemical pesticides. So University of Wyoming insect ecologist Jeff Lockwood decided to use the grasshopper's menu of choice against it.
"We knew grasshoppers were voracious cannibals, they found a dead individual very quickly, and with that sort of speed in a rangeland, you have to suspect there's some kind of chemical cue, and so we tracked down that chemical cue and found it was the decomposing fatty acids in the grasshopper's body that were releasing an odor that was dinner bell for the other grasshoppers," Mr. Lockwood said.
Professor Lockwood knew he'd found a powerful insect bait, but fatty acids were too expensive to purchase in pure form. That's when his team realized that many vegetable oils were high in the same fatty acids as decomposing grasshoppers, and much cheaper than the purified ones. Currently, the only effective and economical pesticides land managers can use against grasshoppers are carbaryl, diflubenzuron and malathion. But these broad-spectrum poisons are not appropriate for environmentally sensitive areas like rangeland. Stefan Jaronski says that's led to the development of biological agents to bring the insects down.
"There is this Beauveria, a fungus that attacks insects. It is commercialized and registered in the United States for use against grasshoppers, and it's quite suitable for these environmentally sensitive areas. The one problem is that given the use rates and the cost of the product, it's not affordable to ... most land managers," he said.
To deal with this problem, researchers looked for a substance that could deliver the fungus more efficiently a medium that could draw grasshoppers to the toxin and so permit more targeted, less expensive applications. Mr. Jaronski says the thick oil of rapeseed, or canola seemed an ideal choice.
"So we thought we'd try coupling the attractiveness of canola oil with Beauveria to increase efficiency of contact, to bring the grasshoppers to the fungus, if you will, and thereby allow us to get good control of grasshoppers but at much lower rates per acre. So the fundamental is dollars per acre, to drop to a level where the average rancher or land manager could begin to afford this material," Mr. Jaronski said.
In addition to its lower cost and greater efficiency, this mix of fungus and canola oil offers important environmental benefits. Because the fungal pesticide is toxic only to grasshoppers and locusts, Beauveria applications leave more natural predators alive to help control any surviving pest populations.
And ecologist Jeff Lockwood notes that there are also human health benefits to using Beauveria rather than chemical pesticides, especially in regions such as Africa and the Middle East where grasshoppers and locusts are not just pests but also a part of the local diet.
"One concern of using insecticide for locust control is that after an insecticide spray, of course you have lots of dead and dying locusts which are a lot easier [for people] to catch than the healthy ones, and so those are likely to enter the human food chain [be the ones people will eat]. And consequently, whatever insecticide you use to knock those to the ground is going to enter the human food chain as well," Mr. Lockwood said.
The two scientists presented their findings at the recent annual meeting of the Entomological Society of America in Florida. Beauvaria-laced canola pesticide is still undergoing field tests against grasshoppers. But if the final results are as encouraging as the initial data suggests, an affordable biological treatment to stop grasshopper infestations might soon be available.
