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Grain bin pests provide potential losses for grain stored in on-farm facilities

by Wyoming Livestock Roundup

As the capacity of on-farm grain storage increases across the U.S., University of Wyoming Extension Entomologist Scott Schell looks at the potential impacts caused by grain bin pests. 

“About $200 million of stored grain loss is a low estimate,” says Schell. “Some of the estimates are as high as $500 million.”

Concerns about grain don’t end after the product is harvested and stored in a bin. 

“We have to take care of grain in storage to make sure it stays in good shape for longer,” he explains. “We figure about a 10 percent loss just from biological degradation. That includes not only insects that are feeding on the grain, but their biological activity, which can create moisture pockets and result in mold.”

If the conditions aren’t right, long-term storage can result in grain loss, as well as forfeiture of premiums due to insect presence.

“Just two live insects per 2.2 pounds is considered not fit for human consumption,” Schell says. “Producers can be downgraded for their quality and not get a premium if they don’t have insect-free status.”

“This is a really important issue,” he adds. 

Integrated management

“The University of Wyoming advocates for integrated pest management across the board,” Schell mentions. “We want to combine many approaches so we don’t rely on one particular thing.”

Without an integrated approach, insects can become resistant to a single treatment used.

“Insects, mice, weeds and rodents can all be dealt with using integrated management,” he says. “The goal of management is not eradication but management with technology.”

Dealing with pests

“The first step in dealing with pests is proper identification,” says Schell. “If we don’t know what the pest is and we don’t know its life cycle, we won’t know how to deal with it.”

Schell notes that insect pests in grain bins can be wide and varied. 

Some insects feed inside the grain kernels, others infest the grain in the fields and others only feed on damaged grains. The life cycle of various grain beetles also differs, with some having multiple generations and others with delayed activity. 

Improper harvesting can damage grain, increasing susceptibility to grain pests, and improper storage can increase susceptibility to problems like mold due to moisture and temperature increases. 

Common offenders 

In the Rocky Mountain West, the granary weevil is a primary pest that causes a number of problems. A primary insect infests the interior of the grain kernels, hatching after eating the inside of the kernel. 

“The granary weevil is very small,” Schell explains. “They have the weevil’s snout and chewing mouth parts.”

The female weevil notches grain kernels and lays the eggs inside the kernel. Afterwards, the female weevil seals the kernel. The eggs hatch and develop inside the kernel. 

“The weevil doesn’t chew an exit hole until after it is ready to go,” says Schell. 

“If we can bring the wheat in from the field, it might look pest-free,” he continues. “We can’t tell if there are weevil there or not.”

“Another primary pest found in the Rocky Mountain West is the lesser grain borer,” Schell notes. “They damage the inside of the kernel.”

Secondary pests

Secondary pests create problems in broken grains.

“We are more likely to see the secondary pests, but we may not recognize them,” Schell comments. “The larvae are really small, and the adults are only about three millimeters in length.”

“Red flour beetles are secondary pests,” says Schell. “They aren’t found inside the grain, and they are found in processing bins, flour mills and whatnot.”

The sawtooth grain beetle attacks broken grain. 

“These insects are very small,” he notes, adding that the mature adults are only two to three millimeters. “They infest grain in the field and are brought in to the storage.”

The warehouse beetle is also a secondary pest that comes from the same family as carpet beetles. 

“Many have the ability to eat anything that is organic in nature,” says Schell. “They are really adapted to feeding, and some species are found frequently on barley.”

Targeting pests

To address grain bin pests, Schell recommends utilizing a six-step program promoted by Colorado State University that emphasizes prevention. 

“The first step is to keep bins clean and in good repair,” Schell says. “We don’t want to have gaps or anything to allow the entry of pests.”

Controlling ventilation and leaks helps to prevent pest issues, as well.

“We also want to clean the bins very thoroughly every time we empty them to decrease the liability that we will retain pests,” he continues. “Using sprays after cleaning is another recommendation. Insecticide sprays can kill insects that may be hiding in grain bins.”

Because many of the pests are very small, Schell notes that spraying them can prevent infestations. 

Several of the pests can also persist for several years, even in empty bins.


When adding a new crop of grain to a bin, Schell says, “We have to fill the grain bin to the proper level.”

“Often, we might have half a truckload and we don’t want to haul it to the elevator to sell, so we pile it on top,” he continues. “That practice can interfere with the proper functioning and drying of the grain.”

Too much grain in a bin can impede drying and encourage mold growth.

“We can suppress pests by controlling temperature and moisture,” Schell notes. 

Grain should be stored clean and dry, at a moisture level of 15 percent or less. 

“Aeration is also very important to keep heat and moisture dissipated,” he comments.

“Next, inspecting grain regularly can reduce problems,” says Schell, noting that the easiest way to make sure moisture and temperature are proper is to regularly monitor grain.

“If we use preventative measures, we should end up with quality grain that we can use and sell,” Schell adds.


Improper storage can increase the susceptibility of grain to mold. 

“We have to keep the right moisture conditions,” University of Wyoming Extension Entomologist Scott Schell notes. “If we keep them too low, that can damage grain, too.”

Insect pests are fairly mobile, he continues, and often they can carry mold spores on their bodies. Other insects feed on the mold.

“Insects essentially transport mold and can inoculate our grain bins,” he adds. 

The foreign grain beetle, for example, is particularly good at spreading mold spores because they carry the spores on their bodies.

Schell spoke at the 2015 WESTI Ag Days, held in Worland at the beginning of February. 

Saige Albert is managing editor of the Wyoming Livestock Roundup and can be reached at

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