In a study conducted by the U of M Biosystems and Agricultural Engineering Department and the U of M Entomology Department, graduate students assessed the survivability of Indian meal moth larvae (the immature stage of the insect that feeds on grain kernels) on three diets: 100 percent whole corn kernels, whole kernels mixed with five to seven percent broken kernels, and 100 percent broken kernels. The study was conducted on small samples of corn kept at room temperature in an entomology laboratory.
“We know that a certain percentage of every generation of insects will die from natural causes,” Wilcke says. However, the more favorable the environment and the better the food source, the greater the percentage of insects that survive. In a test using conventional yellow dent shelled corn, 80 percent of the insects survived on the diet in which all the kernels were broken and 61 percent survived on a diet that contained seven percent broken kernels, but only about seven percent survived on a diet that contained only whole (unbroken) kernels.
These results indicate that if you clean corn to remove broken kernels before the corn is stored, it will be much less likely that stored-grain insects like Indian meal moth will become a problem in the storage bin.
In a similar test using a corn hybrid that was developed to contain higher than normal amounts of oil (high-oil corn), the pattern was similar, but insect survivability was greater at every level of kernel damage. All of the larvae survived when provided with a diet of all broken corn kernels, 81 percent survived on diet that contained 5 percent broken kernels, and 28 percent survived on a diet that contained only whole corn kernels.
These results indicate that it would be helpful to clean high-oil corn before storage to reduce problems with stored grain insects; and that insect problems might be slightly greater in stored high-oil corn than in corn with normal levels of oil.
Although these tests were conducted with just one species of insect (Indian meal moth), there is reason to believe that the results would also apply to other types of stored-grain insects. Indian meal moths are “secondary pests”--insects that feed primarily on broken grain or on molds that grow on broken grain.
Stored grain surveys indicate that the most common stored-grain insects in the upper Midwest are “secondary pests.” This means that cleaning grain to remove broken kernels should make life difficult for our most common stored-grain insects.
Of course, there are other good reasons for cleaning corn besides reducing the risk of problems with stored-grain insects:
- Research has shown that mold (fungi) grows much faster on broken corn kernels than on whole kernels, so cleaning grain to remove broken kernels also reduces the chance of mold problems.
- Broken kernels plug the air spaces between whole kernels, which increases the airflow resistance of the corn. High airflow resistance means that it takes more fan power to provide the airflow needed to dry or aerate grain. Or for a given fan, higher airflow resistance means that the fan provides less airflow, which means that it takes longer to dry or to aerate the grain.
- Broken kernels tend to concentrate under the fill spout when a storage bin is filled. These concentrated areas of broken kernels, which are already more likely to support insect life and mold growth, are also difficult to dry or aerate because they have high airflow resistance and air moves around rather than through them.
- High levels of broken kernels can lead to price discounts when grain is sold.
For more information, see the Biosystems and Agricultural Engineering postharvest Web site, http://www.bae.umn.edu/extens/postharvest/index.html, or contact Bill Wilcke, [email protected] or Colleen Cannon, [email protected].