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Catching Grasshoppers the Old-Fashioned Way

By David Elstein
April 26, 2002

With all the high-tech tools scientists have at their fingertips, sometimes the simplest device is still the best--especially when you’re counting grasshoppers.

A pane of glass and soapy water are all entomologist Dennis Fielding needs to catch grasshoppers. He snags these pests to estimate how many are invading cropland from surrounding areas that don’t have crops. Standard sampling methods, developed on grasslands with relatively sparse vegetation, are based on visual counts. Fielding, an Agricultural Research Service scientist in Fairbanks, Alaska, wants to develop a way to conduct his grasshopper “census” in areas where there is a dense canopy of cultivated crops--especially, small grains.

Grasshoppers have eaten agricultural crops--and lots of other plants--over the course of history. They especially enjoy small grains and vegetables, which is bad news for farmers’ incomes.

Fielding’s traps are based on similar devices that have been catching other insects for perhaps a hundred years. The grasshopper flies into the vertical pane of glass and falls into soapy water. The insect then sinks because the soap breaks the surface tension of the water. Grasshoppers may be attracted to the trap because of the smell of their dead “friends"; they are known to eat dead grasshoppers.

The traps will probably be restricted to research applications because of their considerable cost in materials and labor and the large number needed to get good counts. Fielding had nearly 100 traps deployed on more than two areas. Each field had traps placed near the roadside and also in the area where crops were growing.

Fielding’s research has been under way for two years, and he thinks it may take another two to calibrate and test the traps under a variety of conditions.

ARS is the U.S. Department of Agriculture’s chief scientific research agency.