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Spotlight   | Summer 2012

Hermetic bags save African crop, but not how experts once thought

web bonus Video: Bill Gates was the keynote speaker at a national event to mark the 150th anniversary of the Morrill Land Grant Act. In his speech, he talks about the PICS program. The PICS section starts at 2:21 in the video.
PIC grain bags
Purdue Improved Cowpea Storage bags are opened during a ceremony in Pala, Chad. With the bags, farmers in Africa can safely store their cowpea grain and sell their crop well beyond harvest.

Photo credit: Photo courtesy Beksoubo Damienne

The hermetic grain storage bags that cut off oxygen to weevils and have saved West and Central African farmers hundreds of millions of dollars don't merely suffocate the pests, as once thought.

More than 25 years after introducing the Purdue Improved Cowpea Storage bags to farmers in Africa, entomology researcher Larry Murdock discovered that weevils produce much of their water themselves through metabolic processes. When oxygen in the bags decreases, the weevils cannot use it to create water, and instead of suffocating, they eventually die of thirst.

"When you and I want water, we go to a water fountain or grab a bottle of water," Murdock said. "Insects cannot do that, especially those living in dry grain. They have to get it someplace else."

Murdock led a team in 1987 that developed the PICS bags as a way to combat weevil infestations in Cameroon that discouraged farmers from storing their own harvested cowpea grain. A female weevil can have as many as 100 offspring in one month, and just a few can cause significant loss in a short amount of time. So farmers often sold everything at harvest time, which limited their profit.

With the PICS system, farmers place their cowpeas in a polyethylene bag and seal it. The bag is surrounded by another, identical bag and sealed, and the double-bagged crop is held within a third, woven nylon bag. All of the materials are cheap and increasingly available in cowpea-growing regions.

By Brian Wallheimer


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