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  • Infrared Sensor Counts Insects

Photonics Spectra
Nov 1998
Aaron J. Hand

If there's one thing that bugs the agriculture industry, it's bugs. Insecticides are effective in debugging stored products such as grains, fruits and vegetables, but health and environmental officials realize they are dangerous as well and are enacting legislation against their use.
Alternatives are typically more expensive. "One way of making these alternatives more feasible is to only use them on an as-needed basis," said Dennis Shuman, an electrical engineer at the Center for Medical, Agricultural and Veterinary Entomology at the US Department of Agriculture's Agricultural Research Service. He has developed a device, the Electronic Grain Probe Insect Counter, which does just that.
He takes a common grain probe trap and enhances its capabilities with an infrared sensor. The traditional tubes are placed in grain bins and elevators for long periods, then removed and inspected. Shuman's device allows operators to monitor insect count from a remote computer.

Sensitive to smaller bugs
The sensor head contains an infrared light-emitting diode matched with a phototransistor. Shuman reversed the collector and emitter to give the device a lower gain, allowing the phototransistor to be biased in the linear region, which makes it more sensitive to small insects. The latest versions use matched pairs from QT Optoelectronics in Sunnyvale, Calif., which seem to be working better than previous matched pairs, he said.
Shuman has made several improvements to the probe since he developed the first prototype five or six years ago. For one, electronic noise is not the problem it used to be, according to Thomas Phillips, associate professor of entomology at Oklahoma State University in Stillwater. He operates one of eight evaluation sites around the country on the current version and says he sees more than 90 percent accuracy.
Upgrading the system to use its sensitivity to distinguish between insect types could prove beneficial, Phillips said. "In the stored-grain ecosystem, if you will, we have a whole range of insects," he said. "Some of them are eating the grain, but some are eating the insects that are eating the grain."

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