Stored Product Pest Control

Features - Pest Control

Knowing the Pest is Half the Battle

December 10, 2013

Pests of grain and other stored products have been around for a long time. Recorded control efforts go back as far as 2500 B.C. when the Sumerians used sulfur compounds to protect their crops from insects. Such fumigants and other alternative methods are still used today to rid stored products of insects. (See Fumigant Options, page 40.) But the real key to control and prevention is knowledge.

“Knowing the pest is half the battle in controlling it,” said Insects Limited President David Mueller in a presentation at the Purina Food Safety Symposium. Pests have varying food preferences and habitats; differing life cycles, feeding stages, and adult lifespans; and dissimilar temperature thresholds and abilities for flight and package penetration, Mueller said, all of which are important in selecting the best method of control, and in reducing conducive conditions by which the insects live and breed.

The Differences.

Even among similar insects, there are differences. For example, the granary weevil can survive temperatures as low as 540F, while the red flour beetle will die if temperatures fall below 720F for a period of time. Additionally, some insects feed from the outside of grains or seeds, while others burrow inside to lay eggs which will then develop and feed from the inside. Some feed only as larvae, while others feed as adults.

Additionally, different pests are attracted to different products, and understanding the specific insects that would be attracted to your plant and product is key to control, said Trece Marketing Manager Donna Lingren.

For example, the cigarette beetle is primarily a pest of spices, tobacco, and cocoa; while the Indian meal moth infests a vast array of dry products from flours to nuts and cereals to beans and chocolate. “The Indian meal moth is the #1 feared insect in the stored product industry,” Lingren said. “And it is the most abundant.”

The Similarities.

Despite their differences, the pests also have some things in common, one of which, Mueller said, is that their presence is a symptom of a condition. The condition may be an unsanitary environment, excessive temperature, or moisture content, or other pest-attracting issue. “Understanding these finite conditions that insects prefer can help you spend your time inspecting and managing pests,” he said.

When an infestation appears in a stored product, the first thought is often that it came in with delivery of the raw product. While this is a common means of entry, which makes it critical that plants inspect incoming goods and reject any deliveries that have any sign of stored products (such as webbing, cast skins, larvae, eggs, or adults), these insects also can come in from the outside, said BASF Market Development Specialist Jason Meyers. This is particularly true if the plant is near a field or dump site that attracts pests and the plant structure is not well-sealed—providing entry points for the pests. “Probably a majority of calls we get are associated with pests coming in from outside, and it’s more difficult for PMPs to help in those situations,” Meyers said.

Because of this, a moth or two in a trap does not necessarily indicate an infestation, and pest management companies will have differing thresholds for action. “But it is even more important for plant management to have its own threshold and communicate that to the pest management professional,” Meyers said. “Communication is by far the biggest need between the food facility management and the pest management professional—so that both understand the other’s expectations for the plant.”

Although a single pest does not mean an infestation, that single pest can begin an infestation if conditions are right. It is for that reason that preventive controls are critical. “The biggest thing is sanitation,” Meyers said. Periodic, intensive cleaning is of particular importance in areas of equipment and warehousing where dust, debris, crumbs, etc. can collect and accumulate. “Those are areas we see as becoming the most problematic.

Additionally, he said, pests can come in with deliveries “as a Trojan horse,” infesting materials that haven’t been rotated. “The more you can rotate stock, the less likely you are to have a pest issue,” Meyers said.


Another commonality among stored product pests is the innate need for survival, not only of the individual insect but for the survival of its species as a whole, thus the drive not only to feed but also to mate and breed. For this reason, trapping provides an effective means of both monitoring and control. But because most traps for stored product pests are pheromone based and insect specific, Lingren said, it also provides further reason for the need to know the most likely pests of your product.

Indian meal moth pheromone lures, for example, duplicate the female’s pheromone to attract the male adults. When you understand the lifecycle of this moth—that it can have eight overlapping generations or emergences in a year—and the traps are capturing these adults, “you know there has been a flight emergence,” she said. And, because they are being attracted by the pheromone, she added, “you also know that other males and females are finding each other and laying eggs.”

Based on trap capture, and location of the trap, you then can zero in on hot spots and identify the location of an infestation. This can you help determine where the infestation originated (e.g., from outside or in a delivery) and assist in the decision making for control.

As monitors, traps provide an early warning system that a problem is developing in the plant. “Trapping systems give you a lot of information about insects in your facility,” Lingren said. “If I were a food processor or a pest control operator, I would want to use pheromone traps because they are like a 24/7 employee for you.”

As with so many aspects of food safety, most important for both prevention and control is understanding the risk: the pests that are most likely to infest your product and facility, the most destructive life stages and means of entry, and the most effective methods of prevention and control.

Or, as simply stated by Mueller, “Always start with the insects first.”


Fumigant Options for Stored Product Pests

Once beetles, weevils, or moths infest stored products, they can be difficult to eliminate. The most traditional process of elimination is fumigation, but there are also non-chemical and natural alternatives.

Fumigants are specialized pesticides that act as a gas to kill a pest, explained Tom Phillips, professor of entomology at Kansas State University. All fumigants are toxic, and proper safety precautions must be taken by applicators to manage the risk.

In the U.S., there are three synthetic gases that are registered for use in food or food-related structures: Methyl bromide (which has very limited uses today), hydrogen phosphide, and sulfuryl fluoride. Alternatives to fumigants include heat, controlled atmosphere, insect growth regulators, and biological controls such as predators, parasitoids, and pathogens. Following are overviews of each, as provided by Phillips:

  • Methyl Bromide. Prior to the 1990s, methyl bromide was the most common fumigant used in flour mills, and also was used for a variety of other fumigations, including that of soil because of its high toxicity and relatively quick action. Today, the chemical has just about disappeared as a fumigant, having been identified as an ozone-depleting substance by the international agreement of the 1989 Montreal Protocol. The fumigant was scheduled for elimination by 2005, but the act included an allowance for short-term critical use exemptions, which number just two to three user groups now, and also a standing exemption for international quarantine and pre-shipment.
  • Hydrogen Phosphide (Phosphine). Today, Phillips said, “Phosphine gas is, without a doubt, the most common fumigant used on grains, cereal grains, and oil seeds worldwide.” Because the gas is so lightweight, it disperses well through the grain and dissolves easily into the air, he said. The fumigant also is fairly easy and safe for professional application because it generally is applied as a solid, which reacts with warm temperature and moisture in the air to gradually release the gas. Thus, there is less risk because the gas is not generated immediately. However, it is corrosive to some metals and can damage electrical and electronic systems, so must be used with care. Additionally, several species and local pest populations have developed resistance to phosphine gas.
  • Sulfuryl Fluoride. Sulfuryl flouride has been used by the pest control industry for more than 50 years, but until about eight years ago, it was only labeled for structural fumigation of drywood termites and other wood-boring insects. Today, the fumigant also is registered and labeled for grain and food use. Research is showing that sulfuryl flouride will kill phosphine-resistant insects, thus, it is providing a beneficial alternative for that as well as methyl bromide.
  • Heat. Because high heat will kill insects, stored product pests can be killed by raising the temperature to 122°F and holding it there for several hours. Heat is generally not applied to bulk-stored commodities or value-added products because of risk of damage, but it is growing in use in buildings. However, because the insects will hide or move to cooler locations, it is critical that the temperatbure penetrate all the way through the structure. This can be difficult, particularly if pests have burrowed down into gaps in a concrete floor laid on soil. Nevertheless, heat is used successfully for many mills and warehouses by applicators who know the techniques for best practices. Freezing temperatures also can be very effective and safe for many products, but are often less practical for large quantities as the core must reach 0°F.
  • Controlled Atmosphere. Radically increasing carbon dioxide and/or decreasing oxygen in the air will kill just about any insect that is properly treated. Air is naturally composed of much less than one percent of carbon dioxide; if this composition is raised to 10 to 30 percent, it will kill over a period of several days; so to kill the insects, the CO2 is raised to 60 to 80 percent and held for a period of time based on the susceptibility of the species and life stages present. Decreasing oxygen will suffocate the insects. This is done by displacing the oxygen with an inert gas, such as nitrogen, however this is very difficult to do in buildings because of size and the fact that very few are gas-tight. Low vacuum, which can bring the O2 concentration to a killing one to two percent, can be applied effectively to small loads.
  • Insect Growth Regulators (IGRs). With methoprene or pyriproxyfen as active ingredients, IGRs are very safe pesticides around people and food, Phillips said. IGRs disrupt insect development at juvenile stages making reproduction impossible; they are very effective on grain insects.
  • Biological Controls. This method uses naturally occurring beneficial insects to kill destructive insects. For example, parasitic wasps will sting an Indian meal moth larva to paralyze it and then lay eggs on it. When the eggs hatch, they feed on the paralyzed larva. When initially used, regulators designated the beneficial insects as an adulterant, but after review, the designation was revised to be considered a pesticide and exempted from the requirement of a residue tolerance; however, any such insects would still have to be considered with the tolerance for insect fragments.


The author is Editor of QA magazine. She can be reached at