Preventing Grain Spoilage by Insects, by Jim in New Hampshire

I’m big on food storage and my hobby is finding and photographing beetles. These two interests converge when grain beetles start reproducing in my stored grain products.   I had bought some 50-lb. bags of corn and oats at the Tractor Supply Company store, intending to treat them for insects and put them up in 5-gallon buckets. I never got around to it and eventually noticed tiny grain weevils showing up around the house. The grain had not only become infested with Rice Weevils ^[1] but their droppings had produced a lot of ammonia that turned the oak flooring dark beneath the most infested bag. I dumped 200 pounds of grain out on the compost pile, a free feed for birds, mice, and squirrels. Rice weevils are hardly the only grain beetle to worry about.

Here are some of the others, belonging to eight additional beetle families, with links courtesy of the Bug Guide web site:  

• Oryzaephilus mercator ^[2] – Merchant Grain Beetle ^[2]
• Oryzaephilus surinamensis – Sawtoothed Grain Beetle ^[3]
• Cathartus quadricollis – Square-necked Grain Beetle ^[4]
• Nausibius clavicornis ^[5]
• Lasioderma serricorne – Cigarette Beetle ^[6]
• Rhyzopertha dominica ^[7]
• Latheticus oryzae – Longheaded Flour Beetle ^[8]
• Cryptolestes ferrugineus – Rusty Grain Beetle ^[9]
• Tribolium castaneum – Red Flour Beetle ^[10]
• Thorictodes heydeni ^[11]
• Tenebrio molitor – Yellow Mealworm ^[12]
• Tenebrio obscurus – Dark Mealworm ^[13]
• Typhaea stercorea – Hairy Fungus Beetle ^[14]
• Symbiotes gibberosus ^[15]  

In addition there are moths, flies, and small wasps that lay their eggs in grain products, all of which can ruin your stored food supply if precautions aren’t taken.   Here are three common alternatives for killing off any grain pests that happen to arrive in bulk grains:  

1. Purge the oxygen with another gas. Buy some dry ice (frozen carbon dioxide) or a tank of CO2 ^[16]. Put a few ounces of dry ice in a container of grain. Cover with lid but wait several hours before sealing. The CO2 is a heavy gas and will slowly fill the airspace from the bottom up, pushing out the ambient air containing oxygen. A faster method is to slowly fill the bucket by inserting a hose from a CO2 tank into the bottom of a filled container and cracking open the valve. Then the container can be sealed right away.  

2. Absorb all the oxygen with O2 absorber packets. (You can also use hand-warmer packets [, although they are much more expensive].) This method is best used with a Mylar liner inside the storage container ([food grade HDPE ^[17]] plastic bucket, etc.). Once the O2 absorber packet is added, heat-seal the Mylar bag with a clothes iron against a broomstick or other straight stick or rod, then seal the container.  

3. Add a safe-to-eat physical insecticide, food-grade diatomaceous earth, mixing thoroughly with the grain. I use one cup per 100 pounds of grain. This substance is composed largely of the silaceous exoskeletons of diatoms, tiny unicellular aquatic organisms that died over eons and accumulated in deep deposits of ancient lakes and sea beds long since exposed on dry land. Their exoskeletons have sharp edges that scrape off the protective waxy coating on the exoskeleton of grain pests that permits them to survive in dry conditions. They lose moisture too rapidly to replace and they perish, never being able to multiply. A side benefit to this method is that it abrades the protective coating of intestinal roundworms as well — good survival medicine.

JWR Adds: All three of those methods have proven efficacy. Needless to say, do not be tempted to use any chemical insecticides, since they can be toxic to humans and would also horribly taint the taste of foods. Also, don’t think that by merely sealing newly-bought grains or legumes in airtight containers that you will will protect them from infestation. The chances are quite high that they already have insect eggs larvae present.