Treating dried foods for insects

Some internet authors see that their job is to separate the wheat from the chaff; then, to publish the chaff.

Introduction.

Indian meal moth, flour beetles, saw-toothed grain beetles and carpet beetles are just some of the insects that can find their way into food storage.  There is nothing like the surprise in opening some stored wheat to find either an active infestation with weevils or the results of a past infestation.  So the big question is what can be done?  The first and most important factor is to purchase high quality supplies that are not already infested with visible insects or their larvae.  The second layer of defense is to choose one of the methods below.

Oxygen absorbers or vacuum sealing (recommended)

Some believe that oxygen absorbers are the easiest and most effective method for destroying insects in stored foods⁴.  Insects require oxygen to survive, so removing that oxygen is an effective insect prevention measure.  The oxygen content must be lowered to below 1% and held it there for at least 12 days to kill insects in all stages⁴.

Use.  The same level of oxygen absorber packets for removal of oxygen is recommended for simultaneous destruction of insects.  Basically, 100 cc packets will work for quarts and pint containers, 300 cc packets for gallon containers, and 500 cc packets for 5 gallon containers. 

Dry Ice (recommended)

Dry ice is frozen CO₂. Treatment with dry ice may improve storage life of the grain, but it is not the most effective fumigant for controlling pests in stored grain. The main obstacle is ensuring that the food container is filled to 99% CO2 or more.  At this level, all insects in all stages did not survive.  If the percent CO2 was lower, the effectiveness of the treatment was reduced.  A single treatment with dry ice may be sufficient for long-term storage. Annual dry ice treatments are not necessary unless an infestation is recognized in the stored grain.

Heating

To control insects by heating, preheat oven to 130°F, place grain in a pan and heat for 30 minutes. Grain may also be placed in the microwave and heated on high for 10 minutes.  Heating in the oven and the microwave at these settings will both prevent germination³.   Heating may work for some dried foods, but others may be changed organoleptically.

Freezing (recommended)

To control insects by freezing, 1-15 pounds of grain should be placed in a medium to heavy plastic bag or double bagged and stored in a freezer for 2-3 days. Eggs of insect pests, if present, will not be affected by freezing. Warm grain for 24 hours to allow some eggs to hatch. Repeat freezing cycle. Multiple freeze-thaw cycles may be required.

Diatomaceous Earth (DE) (not recommended)

The use of diatomaceous earth (DE) as an insecticide is a "commercial" alternative to traditional chemical insecticides.  DE is of natural origin, leaves minimal residues on the product and has low mammalian toxicity. DE “inactivates” the waterproof lipids of insects’ causing them to die through desiccation. While overall, DE’s work well as an insecticide, specific DE formulations must be tested for activity in each product and against each insect species.  In addition, while DE is not a chemical hazard it is an inhalation hazard.  Thus, the nature of the silica powder in DE determines the risk.  This makes home insecticidal use impractical and potentially harmful^1,2.

Garlic (not recommended) 

Garlic has been studied as a method of insect control⁴.  Studies showed some success, but the insect destruction was not complete⁴.  Naturally, garlic would add an unnecessary flavor and odor to dried foods.  For that reason it is not recommended.

Bay leaves, chewing gum (mint flavored or otherwise), 10-penny nails, or salt (not recommended)

These treatments are considered old wives tales and there is no research-based evidence that they work. 

References

1. C.G. Athanassioua, N.G. Kavallieratosb and C.M. Meletsisc.  Insecticidal effect of three diatomaceous earth formulations, applied alone or in combination, against three stored-product beetle species on wheat and maize. Journal of Stored Products Research. Volume 43, Issue 4, 2007, Pages 330-334.

2. Subramanyam, Bh. and R. Roesli. 2000. Inert dusts, pp. 321 - 380. In Subramanyam, Bh. and D. W. Hagstrum. (eds.), Alternatives to pesticides in stored-product IPM. Kluwer Academic Publishers, Boston, Massachusetts.  Available here.

3. Glogoza, P. 2005. Bugs in Your Cupboards. North Dakota State University. Available online at: http://www.ag.ndsu.edu/pubs/yf/home/e300w.htm

4. Thompson, J. Dry-Pack Food Storage: Container Options, Oxygen Absorbers and Other Treatment Methods. Available online at: http://extension.usu.edu/weber/files/uploads/J%20Thompson%20Handout1.pdf