Stored Product Pests

Features - Pest Control

Prevention, Detection, and Gatekeeping for Control

December 11, 2014

With the amounts and types of food—both ingredients and finished product—that are stored at food and beverage processing plants, it is all too common for stored product pests to invade. Once in your warehouse, these beetles, weevils, and moths can cause extensive damage and product loss. This can be from contamination of the insects in the food; by their feeding on or boring into grains; or by what they leave behind such as webbing and fecal droppings.

“The main damage these stored food pests cause is product loss due to contamination by the insects themselves or cast skins and pupal cases of the immature stages,” said Insects Limited Technical Director Alain VanRyckeghem.

Additionally, stored product pests can cause a variety of damage in bulk stored raw commodities ranging from loss of volume, mold/conditioning issues, and regulatory issues surrounding foreign material. In the processing, manufacturing, distribution, and retail segments, these pests pose a food safety risk for adulterating items produced or stored.

“They can also cause the recall of products due to infestation and high expense in discarding infested or damaged products,” said Trece Market Manager James Miller. “Insects can also cross contaminate production processes and items stored/distributed in close proximity.”

Stored product pests are typically separated into two categories: primary and secondary feeders. “When/if the commodity becomes out of condition these pests reproduce rapidly which can allow for large populations and cause considerable damage within a short period of time,” Miller said.

Defending against stored product pests can be thought of as comprising four key steps: prevention, detection, control, and “gatekeeping.”

1. Prevention.

The first step in prevention is regular and thorough inspection of incoming products and supplies. Having a standard operating procedure for inspecting—with a flashlight—and sampling all incoming trailers and pallets of food will catch a majority of infested materials and prevent their entry, VanRyckeghem said.

Once the products have been accepted, they need to be protected from additional damage. This could be from material handling or movement, but also may include hot temperatures or high moisture, he said. “Damage resulting in spillage should be ‘cleaned as you go.’ This process ensures spills are cleaned up immediately and broken packages are removed. Sanitation is everyone’s job and that is the most effective way of preventing stored product insect infestations.”

The use of a pheromone monitoring system in transit can enhance the effectiveness of the prevention program, Miller said.

2. Detection

Pheromone-monitoring systems also can be placed in the facility to detect stored product pests that got through your first line of defense or came in from outdoors. “A grid-like pattern of both hanging glue-style traps for flight-capable pests and dome-pitfall style for crawling pests are recommended for finding/narrowing hot spots or high density areas of insect activity,” Miller said. This will help drive sanitation needs and serve as a starting point for visual sightings.

Besides seeing live or dead insects flying or crawling on boxes, bags, or pallets, visual signs of an infestation can include webbing, frass, cast skins, larvae, pupae on or around food products or storage areas, and damaged/out of condition packaging. An insect infestation also may cause the food to have a musty smell.

Signs that VanRyckeghem advises one look for when inspecting for specific insects include:

  • Indianmeal moth larvae are very active and may crawl away from infested food materials to dark areas, so these may be found in crevices and wall/ceiling junctions. Webbing on or in product containers or packaging is a good indication of infestation.
  • Warehouse beetle larva go through numerous molts and leave delicate hairy cast skins on the surface of food or packaging material.
  • Cigarette beetle adults emerge from paper-packaged foods or boxboard containers and create multiple tiny exit holes. These look as though someone has poked the package with a pencil tip.
  • Red flour beetles and sawtoothed grain beetles typically do not fly, so the main signs of infestations are the active adults around the exterior of the food packaging or dead beetles at its base.

Every plant should have a policy in place for response to detection of an infestation—not wait until there is a problem to establish one. This policy should begin with segregation of potentially infested goods, followed by in-depth inspection of surrounding items, immediate involvement of management, and tracking to the source of infestation if possible, Miller said.

If an infestation is detected on incoming materials, it is essential to prevent the product from entering the facility. It may be kept in the trailer and inspected further, rejected and returned to the sender, or accepted and fumigated to eradicate the pest. “The decision is determined on a case-by-case basis,” VanRyckeghem said.

“If an infestation is detected in storage, it may be difficult to determine the origin of the infestation, so the immediate response should be to quarantine or segregate the product from the rest of the stored products,” he added. To help contain the infestation, the product should be segregated in a transport trailer or sealed room with the air temperature set below 60°F, which will suppress the flight and mobile activity of these insects.

Once the product known to be infested is segregated, it is important to inspect the site with a flashlight to determine if the pests were localized or had spread to other materials. Additionally, the area in which the infested product had been sitting should be thoroughly cleaned, with all insects, larvae and eggs vacuumed. “This will allow the plant manager to detect ‘new’ activity on the next inspection, rather than observe ‘old’ signs from the previous occurrence,” VanRyckeghem added. The area also may be treated with residual insecticide, if allowed, and monitoring tools such as pheromone and food traps should be set up to detect activity that escaped the inspections.

3. Control

There are a number of options for control of pests found in stored food products.

Mating disruption can serve as a tool for both prevention and control, Miller said. “Modern advances in mating disruption are reaching new levels daily—ranging from raw commodity storage to retail stores for prevention and control of Indianmeal moth and soon other noted pests.”

Strategically timed, low-impact, insect-growth-regulator treatments or mist/fog applications designed to interrupt the life cycle of the pest also can help to keep pests under control, he said, adding, “In raw commodity storage, monitoring with grain probes and other pheromone systems to determine insect populations is key to treatment intervals and environmental control measures.”

Additionally, all plants should include warehouses in their sanitation and maintenance schedules, with proper training and oversight

The options for controlling pests in stored food products are dependent on where the food/ingredient is within the food production stream. “Raw ingredients may be reprocessed and sifted/filtered or cleaned to remove foreign materials and then repackaged for use,” VanRyckeghem said. “Sometimes a food material could be frozen to kill active stages and then reprocessed.”

The structure that contained the infestation is the target of most pest control activities, he said. In conventional food storage, options include:

  • Fogging with pyrethrin or a Vapona product can knock down the flying moths or beetles, preventing further spread.
  • Crack-and-crevice treatment with a residual is important for crawling adults and immature stages.
  • In organic facilities, cool storage temperatures (60-65°F) and lower relative humidity (40-45%) can stop many of the common stored product pests from laying eggs and developing into adults.
  • Fumigation with phosphine, which has a wide range of raw and processed food products on its label, can be another option for temperature-sensitive foods. However, VanRyckeghem said, “Most often a food product that is contaminated with insects cannot be salvaged, especially if it is designated for human food, and must be disposed of to the animal feed stream or landfill.”


4. Gatekeeping

Once prevention, detection, and control strategies are put in place, ongoing vigilance and “gatekeeping” will serve to evaluate the efficacy of the program and reduce the potential for infestation. This should include monitoring with pheromone and food traps, detailed flashlight inspections to locate hidden infestations or conditions conducive to infestation, food safety risk assessments performed on as-needed and annual basis, and the use of a pest-sighting logbook with facility schematics for mapping areas of interest or suspected infestation.

Additionally, all facility employees (management and workers) should undergo at least annual training in modern pest prevention and management techniques by a competent instructor, Miller said. This will ensure your workforce is educated and aware of signs and the need for immediate response and control. “The more eyes on the facility the better.”


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