Stored Product Pest Control

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.
 

Trapping.

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.”

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