Stored Product Pests

While any grain-based products can be highly susceptible as food for stored products pests, it has been found that wheat products, rice, pastas, flours, and flavor and baking mixes are among the most susceptible. This is due primarily to the number and variety of pests attracted to these foods and the nutrition that the foods provide to help sustain the life cycle of the insect.

But just as important as the type of product is its packaging. Just about any food will be susceptible to pests if its packaging is open, damaged, or insufficient. “There’s some insect out there that will take advantage of that,” said IFC Staff Entomologist and Product Manager Chelle Hartzer.
 

Packaging.

Some of the most protective packaging materials are high-barrier polyethylene plastics, barrier foil bags with heat-sealed openings, metal cans, and glass jars, said Trece PCO Market Manager James Miller. “Pretty much anything that would keep out air and prevent spoilage of the product contained within.”

There have been many years of research and numerous materials applied to or incorporated into packaging materials to attempt to insect-proof them, said Clark Pest Control Director of Education and Food Safety Al St Cyr.

These have included various essential oils—which have produced overall unfavorable results due to odor or taste transfer; IGR application—which have had some success; and insecticides applied as a final coating on boxes or multiwall bags—which, too, has shown some success.

However, St. Cyr added, “the most achievable goal is to produce packaging that seals properly to avoid insect invasion and penetration. Any packaging that has stitching or vent holes or is loosely woven is a poor choice for insect control. Tightly sealed is the key.” Currently, multi-wall, hermetically sealed pouch-type packaging appears to meet this important criteria, he said.

On the other hand, insects are very aggressive, so you can’t really design a package that is completely insect proof, said ProvisionGard President Jim Bagwell. “It does take longer for an insect to penetrate a 130-mil stand-up pouch, but most will seek out the leaking seal and easily invade those packages first. Any package that has glued seams is at the highest risk.” 

This is also because of the variety of ways that insects can get into packaging. Some insects are more adept at chewing through it, while others are good at finding holes, Hartzer said.

Even sewn seams, which provide more protection than gluing, have some risk, particularly with pests such as the Indianmeal moth. While the insect itself can’t get through holes, the moth will lay its egg on the outside of a hole; when the egg hatches, the tiny larva senses food and drops in to feed, said McCloud Operations Process Manager Anna Getchell.

Some plants will shrink wrap items for further protection, however this still allows for some insect entry points. “But,” Getchell added, “any extra packaging will definitely help—it is one more challenge for pests to deal with.”

In addition to the packaging materials themselves, some packaging practices can increase the risk of pest invasion. As such, Miller said, quality controls and checks should include calibrating of laser etching of batch/lot numbers so as to not create small entry points through the package. Additionally, “modified environments (e.g., nitrogen filling) inside packaging are beneficial to preventing infestation, but they are more of a quality control for freshness of product. The potential contamination left from dead insects inside would be unsatisfactory.”
 

Storage Practices.

Storage practices and the warehouse environments also can contribute to pest infestations—or aid in protection.

“Insects are a symptom of a condition,” said Insects Limited Owner Dave Mueller. When the temperature of a structure reaches about 65°F, you can start seeing Indianmeal moth activity. If it reaches 72°F, you will start to see cigarette beetles and warehouse beetles begin to fly.

“This is important to remember because pheromone traps will not show trap catch at lower temperatures, because the pests can’t fly at that temperature. However, they still may cause a customer complaint,” Mueller said.

Secondly, an understanding of when the first generation emerges will offer an opportunity to destroy the “seeds” that will eventually emerge into future generations during the warm summer months, he said. If you wait until late summer to reduce customer complaints, it may be too late. The first generation is the time to apply preventive pest management.

“The lack of control over the environmental conditions and practices easily allows infestation to be introduced and then flourish,” St. Cyr agreed. This is partly because a plant often will base its population estimates on the visible adult population, but, in reality, the adults represent only 4%-6% of the actual population. Because stored product pests have short development cycles, the populations can explode quickly, only getting attention when high numbers of adults are seen.

To help reduce the potential of such infestations and population explosions, plants should judiciously practice first in/first out stock rotation. This reduces the risk of both insect and rodent infestation by ensuring no one product is left unattended in storage and is used in the processes before a new product is opened, Miller said.

It is also important to take the entire length of the supply chain into consideration, Bagwell said. “Trucks, distribution centers, and more trucking to the retail environment can significantly increase the chance and time it takes for insect growth to reach consumer impacting levels.”  ProvisionGard has conducted warehouse studies measuring full pallet infestations over a 90-day period. Although integrated pest management practices were followed, every box of the pallet was infested within 90 days, he said.

Stored product pests develop from egg to adult in about 30 days, Getchell said. So if a product sits on a shelf for a year, it could yield 12 generations of the pest.

Customer complaints on stored products are often caused when the adult moth or beetle lays its eggs on finished product sitting in the warehouse or retail store, Mueller said. If a product sits for several months, it will create a rancid odor that is detectable by gravid female moths, so that is where she will drop her eggs. The product then becomes the “nova” for an outbreak that spreads to other products in the warehouse.

The longer a product remains in storage, the more susceptible it is to infestation, St. Cyr said. But when first in/first out rotation is practiced, the products undergo closer evaluation earlier so problems have a higher likelihood of being spotted and dealt with. Additionally spillage or leakage from the products is removed quicker and does not serve as a food patch or refuge for insect development. “Essentially any cereal-based material held for too long under unsanitary conditions is highly susceptible to insect infestation,” he said.

For this reason, Miller said, “any expired food products and ingredients should be immediately removed from the facility and placed in a regularly serviced trash receptacle. The key is regularly serviced as to prevent attraction of unwanted pests including rodents, birds, insects, etc.”

Damaged and re-workable products/ingredients should be held for inspection and processed in a designated area of the facility. “This area should be considered a high-risk zone for pest activity, and enhanced pest prevention measures should be put in place,” Miller said.

Use of an exterior storage vessel would be even better, he added. This would ensure no cross contamination or translocation of pests between damaged and good products elsewhere in the facility.

Not only should damaged or expired food be removed from the facility, but all associated spillage needs to be located and disposed of in a compactor or other waste container not connected directly to the facility, St. Cyr said, adding, “Once the integrity of the packaging of raw materials or finished goods has been compromised, it has to be treated as contaminated and not used to produce human food.”

Even once the infested or contaminated product is separated from other product, it should be closely monitored, Hartzer said. Place monitoring devices around it, including insect traps and rodent glueboards to monitor for and protect from further pest populations.
 

Lighting and Ventilation.

Other warehouse environmental controls that are important in control of stored product pests include proper lighting and ventilation.

“For stored product pests, lighting is more key for humans taking care of the product and inspecting and protecting the product,” Getchell said. As she explained, it is important that evidence of pests is quickly detected; to enable this, the warehouse needs to be well lit. “Some stored products pests are drawn to light; some are not,” she said. “So lighting [inside the warehouse] is more important for us protecting the food than for stored product pests as a group.”

That said, because insects can be attracted from the outside to interior lights, selection and placement of lighting inside and outside of the facility is a major component of the hygienic design system, Miller said. In general, lighting should be mounted away from the exterior structures and interior lighting should not be visible from the outside.

This is because exterior lighting mounted on a building above or near entrances or doorways can act as an attractant for insects after dark, St. Cyr said. “This increases the potential for insect entry into the facility.” Additionally, because roof lighting attracts many insects to the roof area, it should be “On Demand,” not left on all night.

While there has been something of a shift from sodium vapor to LED lighting for reduced insect attraction, “the jury is still out on that,” Hartzer said. Current research studies are indicating that attraction is dependent on the wavelength of the LED, with different insects more or less attracted to different wavelengths.

Whether discussing lighting, ventilation, or any other exterior to interior attraction and access, the key is to “make sure the outside stays on the outside and the inside stays isolated from that,” Hartzer said.

Ventilation is important in this because people don’t think about it much, she said. If the filters and screens are not maintained and regularly inspected for cleanliness, fit, etc., they could be allowing insects and debris to be pulled in from outside.

Proper ventilation is also important to prevent the growth of mold and enable proper functioning of pheromone traps, Getchell said. Insects communicate with pheromones to decide when to mate and aggregate.

Because these pheromones (originating from other insects or pheromone traps) are communicated through the air, ventilation can play a part in monitoring with pheromone traps. If ventilation is not properly balanced, the pheromone may reach the insects or may be too concentrated in a single area.
 

Sanitation & Exclusion.

Although the purpose of this article was to focus on packaging and warehouse practices for reducing insect risk, no such discussion would be complete without at least a mention of sanitation and exclusion practices, which are essential to any pest control and prevention effort.

As such, Miller said, “prevention-based integrated pest management (IPM) programs provide the best environment for food safety and will alert you to risks at your facility sooner than a traditional reactive pest control program.”

All sanitation and food safety personnel should undergo annual instruction in modern IPM and pest prevention techniques from an expert and tenured instructor.

“It all starts with detailed inspections to identify issues,” St. Cyr said. “Develop a plan to address the issues noted or those you suspect will develop over time; structure your programs; develop your cleaning schedules and procedures to support the work you need done; train and educate the people as to what and why things need to be done a certain way.”

Sanitation and exclusion form the front line of defense, Hartzer said. Pests need food, water, and shelter. But because it is difficult to eliminate these completely, you need to try to reduce the amount and access. This equates to better sanitation.

With inadequate food, water, and shelter, insects will become stressed, grow slower, and reproduce slower. Thus, she said, “sanitation is incredibly important because it just makes everything a lot easier to deal with.”

From the warehouse structure to the equipment used within it, ongoing maintenance and sanitation are critical to reducing risk of stored product pests. As St. Cyr said, “Your building and equipment were only new the moment the last screw was installed. From then on it has been used and has issues.”

Stored Product Pests
For more information on stored product pests see:

• Prevention, Detection, and Gatekeeping for Control http://bit.ly/1Jsl8Dj
• Knowing the Pest is Half the Battle http://bit.ly/1LOnvpI
• Combating Millions of Years of Evolution http://bit.ly/1LOnB0F
• Pest Presence = Conducive Conditions http://bit.ly/1Q49H9o

The author is Editor of QA magazine. She can be reached at llupo@gie.net.