Bad Bugs: Indian Meal Moth

by Alain VanRyckeghem, BCE Technical Director

What is the most critical damage caused by Indian meal moths – individually or as a whole?

Indian meal moths (IMM) either directly consume the stored food product, (bird seed, pet foods, candy bars etc.) and contaminate it with their presence, webbing, and waist products, or they indirectly contaminate product (food and nonfood) in storage from wandering larvae in search of pupation sites. One infested package of product can be a source of larvae that search out other food products to continue feeding or usually to pupate on the surface or interior spaces of the packages. Perfectly sealed packages that contain baby formula, for example, may have no infestation, but the presence of larvae on the container will cause consumer complaints and rejection of the product. This is essentially collateral damage from another food product.

Why is monitoring for IMM crucial, and what is the best way to monitor?

Monitoring for IMM is designed to be an early warning system. Detection of a couple of moths early in the season can help prevent or reduce further outbreaks during the summer and fall. Traps with sex pheromones to attract male moths are a tool that can operate 24 hours 7 days a week and can be placed in any environment. Placement can be in a grid system to detect recent invasions or can be targeted (concentrated) to monitor selected storage areas or help pinpoint the infestation.

Moth traps need to be monitored weekly, due to the trap’s short life cycle. 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. Lure and traps are to be replaced according to manufacturer’s recommendation which is usually 8 weeks. All traps and lures should be replaced at the same time. Do not stagger the replacement schedule as this leads to old lures stationed beside new lures, resulting in misinterpretation of the source infestations.


What are the steps that should be taken if IMM are detected?

If IMM are detected, inspection of product near the monitors with most activity is necessary. Flashlight inspections to find active larvae, webbing, and food spills are the primary goals of the inspection. Detection of insect activity will require movement and segregation of the product for further action. This may include cleaning, disassembly, fumigation or disposal. Pallets with insect activity should be covered with a PE pallet cover before moving to reduce accidental dispersal to uninfested areas. Sanitation issues should be cleaned up and discarded outdoors in an approved dumpster system. Continue monitoring traps at the area of original activity and adjacent traps. Further activity will require repeated inspections.

How can IMM moth infestations be prevented?

The first line of defense to prevent infestation of a facility is to stop infested materials from being accepted at the receiving areas. This requires receivers to be aware of the presence of 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. These are clear signs of activity and should not be ignored. Detailed inspection can locate these products with activity and should be rejected. The potential use of a pheromone trap in the trailer placed by the vendor at the time of shipment can also give an early warning to the receiver if this trailer has moth activity.

Is there anything else I should be aware of about IMM activity?

Indian meal moths are temperature dependent. Moth flight and reproduction usually does not occur when the environment is below 64 °F. The absence of Indian meal moths in pheromone traps in cool warehouses or cold trailers during shipment is not a fool proof way of determining if moths are present or if larvae are actively feeding on stored product in storage. At these times, a proactive inspection program by the PMP or in house sanitarian is recommended.


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