The mention of stored product pests most often calls to mind beetles, weevils, or moths that infest grain products in silos, food processing warehouses, or even home pantries. While that is the pest management industry’s general thinking on the term, there always will be the uncommon pest in an unexpected food or location that will defy the standard of stored product pests and require innovative solutions. Following are a few such cases and the lesson learned from each.

Eliminating Sugar-Seeking Wasps

PROBLEM: A sugar company’s late summer/early fall deliveries of granulated-sugar tanks were being rejected because wasps were found in the tanks upon delivery to the customer. The wasps were discovered dead and lying on top of the product in a filled car at the destination. “However,” said Zistos President Bob Levine, the company’s video inspection system supplier, “Tank inspection with the tank-vision system did not detect any sign of wasp intrusion in the product prior to shipment.” So, having been told that wasps can chew through the gasket material around the hatch on the manway into the rail tanker, the company then suspected that the contamination was happening en route. “Although the sugar company did consult with an entomologist, no confirmation was able to be made of where and how the wasps were getting in, so the company continued to be faced with the issue,” Zistos said.

SOLUTION. To determine what might be happening and how it could be solved, QA consulted with Bill Robinson of Urban Pest Control Research and Consulting. His response: “These are yellowjackets that are seeking carbohydrates/energy late in the season, as there are no larvae remaining in the colony to provide the sugar food for workers when they return with food for the larvae. (They feed the larvae; the larvae feed them.) Late in the summer, yellowjackets seek any source of sugar, usually liquid. They have chewing/lapping mouthparts, but I don’t think they are ‘chewing the sugar’; most likely there is enough moisture on the surface for them to use their lapping mouthparts. This large quantity of sugar might be a strong attraction for a local colony.

 “Yellowjackets do not forage far from the nest site, but they can wander off. Even in late summer they return to the nest at evening. So, the yellowjackets causing this problem are local in a sense that the nest is close. It could be an above-ground nest or below ground. But, they are not chewing their way into the sugar source. The intrusion of these yellowjackets could occur at either end of the supply chain, but not in route from one to the other. Trucks may stop to rest, but that is usually at night when these wasps are not flying.

“Thus, as a prevention/precaution, both ends of the supply chain should use wasp traps starting in mid-summer and continuing to the second frost. These traps will pull in workers as they forage in the fall and slowly reduce colony size.” 

LESSON LEARNED. While it is not known, without further inspection, whether the wasps were nesting near the sugar company or its customer’s facility, both ends can initiate means of control to prevent a further issue.

Detail Cleaning For Control

PROBLEM. In providing consultation for both food facilities and pest control companies, Technical Directions Consulting Entomologist Mike Holcomb recently received a photo and information on warehouse beetle (Trogoderma) larvae found in accumulations of product fines. A contract pest control operator (PCO), with whom Holcomb has work for more than 15 years, had found the dozens of yellow/white worms in the accumulated fines of a food facility. “These are the kind of infestations we are finding in equipment, slide gates, dead ends of conveyors and on ledges of equipment, on wall and ceiling beams, conduit, and pipes in difficult to access areas,” the PCO stated.

SOLUTION. In addition to describing the problem, the PCO explained his solution. “We have been cleaning and treating these areas, which the pheromone trap counts are reflecting. It is labor intensive, but effective. It also reduces hundreds of gallons of non-ecofriendly fogging materials from being introduced into the facility.” Furthermore, he said, fogging the plant without the inspection, cleaning, and treating did not prove to be as effective when compared to historical trends. 

LESSON LEARNED. “This example clearly demonstrates the importance of ‘detail cleaning’ to the success of your integrated pest management program,” Holcomb said. The hard-to-reach areas where organic debris accumulates (insect resource sites such as overhead ledges, corners, inside equipment, etc.) can become hot spots of insect activity if left unattended. But detail cleaning is not easy; it requires more time and resources than general or aesthetic housekeeping, and it is made more difficult by insanitary design of equipment and facilities.

“In my experience working with various milling industries, I have observed that structural features and food manufacturing equipment that are difficult to access and clean, won’t get cleaned. At least they won’t get cleaned with the intensity and frequency necessary to disrupt the insect breeding life cycle,” Holcomb added. But, as the PCO pointed out, detail sanitation leads to reductions in pheromone trap counts over time. Thus, he relies on monitoring tools to orient sanitation effort toward insect resource sites, and to trend his progress week to week and season to season. “Whether he is aware of it or not,” Holcomb said, “this proactive sanitation approach — resource reduction — helps the plant to comply with two of FSMA’s most important food protection requirements: continuous improvement and prevention, and one of GFSI’s most strident food protection standards: verification.”

Not only does such an organized detail cleaning program enable food processors to use less intrusive pest control techniques and have a “more ecofriendly,” reduced dependency on pesticides, it reduces non-productive downtime that results from reactive pest control such as fogging or fumigation. “After all, when the plant is shut down and commandeered by the pest control operator to correct an epidemic insect infestation, deep-dive sanitation, preventive maintenance, and general plant and equipment re-tooling opportunities are lost,” Holcomb said.

A Sensitive Situation Solution

PROBLEM. Indianmeal Moths (IMMs) are a common pest of dry pet food and, in turn, the pet stores that sell it and the areas in which the food is stored. Like sensitive areas of food processing plants, pet-food stores are particularly challenging as the methods of prevention and reactive control are restricted, in this case to avoid harm to non-target animals – the pets. One such pet store had hundreds of IMMs flying in the store, which resulted in a call to McCloud.

SOLUTION. “Due to the sensitive nature of the establishment, we decided to use non-chemical methods of control to minimize the impact on non-targets,” said McCloud Services Training Manager and Entomologist Anna Berry. “Our first step was to narrow down the probable source.”

Use of pheromone monitoring traps pointed to the dog-food section, but it was two aisles long with over 500 bags of product. So to find the source, they considered the behavior of the pest, the consumer, and the store. IMMs need 30 days or more to develop from egg to adult, so the longer a bag sits in storage, the larger the population becomes, and the more likely it will spread. “Upon assessing the inventory, we saw that medium-sized bags were purchased more often than the large and very large bags,” Berry said. This is primarily due to size as it is more challenging for customers to move a 25-pound bag of dog food than a 10-pound bag, so the larger bags typically stay on the shelves longer, she added. Though some establishments strictly follow first in/first out (FIFO) protocols and move older bags to the front of newer ones, the larger bags still sit on the shelves longer. So, focus was placed on the inspection of the shelves with larger bags. Because there also is likely to be more evidence of IMM activity the longer a bag stays in storage, the outside of the large bags was inspected. Two were found with webbing in the seams — characteristics of IMM activity — as well as pupal casings, indicating larvae had left the food, pupated, and emerged as adults. “When we opened these two bags, we found over 500 Indianmeal moth larvae in both,” Berry said. “The solution was then simple: freeze and dispose of these two bags, thereby eliminating the source.”

LESSONS LEARNED. “Never underestimate the power of a systematic inspection coupled with knowledge of the pest and facility,” Berry said.

It can be overwhelming to have an infestation and intimidating when typical tools (such as chemicals) are not applicable, as is often the case in sensitive areas of food processing plants as well. Knowing the behavior and preferences of the pests and details of an establishment’s practices can often enable the discovery and efficient elimination of the source of the infestation.

Sanitary Design To Combat Pests

THE PROBLEM. Food producers and distribution centers have an obvious struggle with stored product insects — as one of Insects Limited’s Pennsylvania food company customers recently found. If you’re not convinced — deploy a multi-species pheromone trap and check it the following week, said National Sales and Marketing Manager Tom Mueller. Depending on the condition of the facility, you’ll find an alarming number of food-infesting insects and many different species. “One reason is the difficulty sanitation managers have removing the food debris from the footers needed to hold up sturdy shelving,” Mueller said.

Citing Reducing Customer Complaints in Stored Products by David Mueller, he said that one solution could be to vacuum the collection of food, but the time it takes to go through a one- to two-million square-foot food warehouse and vacuum all the boots is quite considerable, he explained. Another solution could be to spray the footers with insecticide which also takes a great deal of time and does not eliminate the food source. But the insects will simply return after the residual has disappeared, he said. This problem was enough for the Pennsylvania food company to make some changes.

THE SOLUTION. The facility already had a sanitation schedule where sweeping, utilization of a scrubbing machine, and rubbish removal happened regularly, but no matter what, food debris still found its way into the racking footers. “The solution was to insert concrete with a slanted top into the racking, preventing the accumulation of food build up and making it far easier to keep the facility clean,” Mueller said. Any food that made its way to the void fell off the concrete slant and was swept up with the facility’s sanitation program. Now pheromones are used to locate where construction modification is needed rather than simply to monitor for increased populations.

LESSON LEARNED. Although construction engineers are not sanitation managers or entomologists, Mueller said, with a little creativity and a simple modification to existing equipment, effective pest management can become much easier. Insects are a symptom of a condition. “Eliminate the condition to eliminate the insects and effectively reduce customer complaints,” he said.

Pest and Diseases Image Library,

Leave No Stone Unturned

THE PROBLEM. A spice factory was having a severe infestation of cigarette beetles and called on Syngenta Professional Pest Management Technical Services Manager Chris Keefer to investigate. The factory, which was thousands of square feet, received spice shipments on a nearly daily basis and was in operation 24 hours a day. The only scheduled downtime was for full-scale regular sanitation events, and the sanitation was superior at this facility. After several thorough inspections with the quality control and entomology personnel, the infestation was discovered to be on the top of rafters above the plant processing floor (unseen from below), where spice dust was settling from the milling process. These small volumes of food dust were enough for the cigarette beetles to complete their life cycles. After copulation, the adult females would fly up onto the rafters to lay their eggs. Larvae would hatch and feed on the spice dust on top of the rafters, pupate, and then emerge as adults.

THE SOLUTION. To eliminate the infestation, the suspected food was removed and quarantined. The plant floor was fogged twice, and some of the equipment and spices were fumigated. The plant then changed its inspection/sanitation process to include sanitizing the rafters on a more regular basis.

LESSON LEARNED. It’s important to understand that insects only need minimal resources and a short amount of time to be successful. Thus, the lesson learned from this infestation is to leave no stone unturned during your inspection.

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