text: Hermetic Bags Save African Crop, but Not How Experts Once Thought - The Crop Site
  US & AFRICA - The hermetic grain storage bags that cut off oxygen to weevils and have saved West and Central African farmers hundreds of millions of dollars by putting the brakes on the insects' rapid multiplication don't merely suffocate them as once thought, a Purdue University study shows.
  More than 25 years after introducing the Purdue Improved Cowpea Storage (PICS) bags to farmers in Africa, Larry Murdock, a professor of insect physiology, 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.
  Professor 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, so just a few can cause significant loss in a short amount of time.
  "After three or four months, everything is destroyed," Professor Murdock said.
  "At harvesttime, grain was at its lowest price because there was an abundance of it," Professor Murdock said. "They couldn't store their cowpeas to eat later because of the weevils, so they would sell everything in the fall. Later in the year, they had to buy cowpeas, an important food, which by then cost two to three times as much. They would sell low and buy high. It's a very bad situation."
  The PICS program is in 10 African countries now, and the goal is to have more than half of all cowpeas stored on farms in West and Central Africa in PICS bags by 2012. Jess Lowenberg-DeBoer, Purdue associate dean and director of International Programs in Agriculture, said more than 1.75 million bags have been sold in West and Central Africa in the last five years.
  Demonstrations on the bags' effectiveness have been done in more than 31,000 villages. The program is expecting 3.4 million households to adopt the PICS bags, saving them about $150 annually – about half a billion dollars per year in saved grain each year overall.
  "The insects are like hard-rock miners chipping away to get something to eat," Professor Murdock said.
  "The PICS bags, a form of hermetic storage, work because depriving the insects of oxygen causes them to cease feeding. This leads them to stop growing, developing and reproducing, which prevents them from becoming a problem," Professor Murdock said.
  Professor Murdock calculated that an average weevil needs at least 7 milligrams of water over its lifetime, but it could only get about 1.4 milligrams from the moisture trapped in the cowpeas they eat.
  Professor Murdock said that while the discovery answers questions about the process, it also suggests ways to improve it. This works reveals that lowering moisture content would enhance the technology's effectiveness.