Indian Meal Moth (Plodia interpunctella). One of the most common of all stored product pests, it feeds on grain, nuts, dried fruits and processed foods. Groupings of up to 30 eggs are laid on the food surface, with the hatched larvae trailing webbing as they crawl and feed.
USDA ARS/Scott Bauer

Moths are one of the predominant stored product pests of both ingredients and finished products in the warehouse. Because they are able to fly from area to area, they can disperse their eggs fairly rapidly across an array of food, contaminating and damaging grains, cereals, pet foods, dried fruits, and even chocolates.

But while it is the adult moths that are most readily seen, it is the moth larvae that cause the most damage. “The larvae of these moths do considerable damage to stored product by eating the product and leaving behind their waste,” said McCloud Training Manager and Entomologist Anna Getchell, adding, “The economic damage caused by these pests is often greater than the food safety risks. Food they’ve infested is hard to sell, as the food is laced with webbing, fecal matter, and moltings; resulting in recalls, returns, and rejection.”

Almond/Tropical Warehouse moth (Ephestia cautella). Similar in size and food preference to the Indian meal moth, it is most often found on nuts. Able to survive outdoors, it is most common in the western and southern states, but it can be transported anywhere in goods.
CSIRO

In addition, some larvae will consume stored food product such as bird seed, pet foods and candy bars, said Insects Limited Technical Director Alain VanRyckeghem, and a single infested package of product can be a source of larvae that then search out other food products to continue feeding or to pupate on or in the packaging. For example, a perfectly sealed package of baby formula may have no infestation, “but the presence of larvae on the container will cause consumer complaints, and rejection of the product,” he said. “This is essentially collateral damage from another food product.”

While causing contamination of the food, the webbing that many of the moths spin is difficult to remove, has been known to clog food-conveying systems, and can lead to sanitation deficiencies, added Trece PCO Market Manager James Miller.

Keeping your food products safe from this moth damage and contamination involves a four-phase system of monitoring, inspection, control, and prevention.

MONITORING. “Monitoring for stored food moths is designed to be an early warning system,” said VanRyckeghem. “The objective is to detect sudden rises in catch rates indicating a recent introduction of infested product, or a sanitation issue that has been overlooked.” As such, he said, detection of a couple moths early in the season can help prevent or reduce further outbreaks during the summer and fall.

Without the use of monitors, it can be difficult to know there is a problem until there are a number of adults flying around. Then that population can explode, resulting in further infestations that are more difficult to control.

Mediterranean Flour Moth (Ephestia kuehniella). Common across the U.S., it feeds primarily on flour, grains, beans, and dried fruits. Like the Indian meal moth, eggs attached to the food surface and webbing spun by the larvae are key signs of infestation.
Andy Reago & Chrissy McClarren

Sex pheromone lures are the best monitoring tool for detecting stored-product moths, Miller said, as the monitoring systems also enable determination of population size, as well as verification of corrective actions taken in an IPM Program.

As explained by Getchell, the pheromone monitoring traps are sticky tent traps with a sex pheromone which attracts the adult males. Males believe the scent to be emitted by a female ready to mate, so they fly within the plume of the pheromone to find her, only to find that they’ve been tricked: there is no “her” and they are stuck to the glue of the sticky trap.

These traps are effective in monitoring for moth presence because they can operate 24 hours a day, seven days a week, and can be placed in any environment, VanRyckeghem said. Placement can be in a grid system to detect recent invasions, or it can be targeted to monitor selected storage areas or help pinpoint an infestation.

However, it is important that the traps not be thought of as a control method. “Far too often people consider pheromone monitoring systems as ‘mass-capture’ traps,” expecting that the traps will solve an infestation, he said. Because the traps attract only the adult male, training and education on the effective use of monitoring systems is crucial to a successful food IPM program. Additionally, Miller said, “Where you have stored product moths, you almost always have stored product beetles.”

INSPECTION. If moths are detected through monitoring, the next step is to conduct a thorough inspection to identify the species and determine the source. This should start with examination of the product nearest the monitors with the most activity, using a flashlight to search for signs that include active larvae, webbing, and food spills that could be attracting the moths.

As with all pests, the goal is to eliminate the problem at the source. “The moth adults will point us to the general direction of the infestation, but evidence from the juvenile stages will really tell us if we’ve found the source,” Getchell said. Thus, the inspection should focus primarily on stored foods with emphasis on older or forgotten product and the shelving/packaging that the product is on or in.

Webbing, which is typically found in nooks and crannies of the product, packaging, or shelving is a clue that the source is nearby, and Indian meal or Mediterranean flour moth larvae may be seen crawling in the product, she added. Because Angoumois grain moths develop inside the kernel, the larvae are not visible, so the existence of exit holes in the kernels is evidence of an infestation of these moths.

CONTROL. “Detection of insect activity will require movement and segregation of the product for further action,” VanRyckeghem said. “This may include cleaning, disassembly, fumigation, or disposal.” Pallets with insect activity should be covered before being moved to reduce accidental dispersal to uninfested areas, and sanitation issues should be cleaned up and the waste discarded outdoors in an approved dumpster system.

Angoumois Grain Moth (Sitotroga cerealella). Found around the world in mild climates, the larvae feed inside kernels of corn and grain, causing significant damage before an infestation is detected. One sign of its presence is an unpleasant smell.
CSIRO

PREVENTION. Once all infested product and moth life cycles are removed, steps should be taken to prevent reinfestation. These should include:

  • Continued monitoring at the area of original activity and adjacent traps, with any further activity spurring repeated inspection
  • .
  • Keeping product sealed and protected in a clean environment at all stages from farm to fork.
  • Maintaining a clean and pest-free environment in the plant and ensuring all food is put into well-sealed packaging.
  • Implementing a good sanitation and product rotation program to decrease the risk that moths pose to stored product.
  • Rejecting infested materials at the receiving areas. This requires receivers to be knowledgeable about webbing on boxes or bags, live and dead larvae in the stretch wrap, and live moths flying out of the trailer or off a pallet.
  • Use of a pheromone trap in the truck trailer, placed by the vendor at the time of shipment, also can provide an early warning of moth activity in the trailer.

The source of most stored product pest moth infestations is incoming goods, Miller said, so a rigorous incoming goods inspection program, supplier inspection program, and use of monitors inside transport containers/trailers can enable you detect a potential problem before it gets in your plant. However, Miller added, some moths also will fly in from outdoors, so occasional exterior monitoring also should be considered. “Never overlook outside environmental activity of the Indian meal moth,” he said.

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