Indian Meal Moths (IMM) are our most common stored foods moth pest, and one reason is because of their diverse food choices. In addition to just about any food material based on grains they also infest nuts, dried fruit, powdered milk, candy bars for the chocolate or nuts in them, pet foods, bird seed, spices including peppers, rodent bait, and even dried flowers. They may even infest fresh fruits if they can find slightly damaged areas. They breed rapidly, with females producing around 300 eggs, and the larvae are very mobile, often leaving the infested food and wandering throughout a structure to find the perfect place to pupate. All of this makes it more difficult to isolate the problem and they may be infesting a multitude of packages.
The adult moths fly very well and it is absolutely amazing how quickly they can spread throughout an entire structure and multiple floors from a single origin within one infested package. They are strongly attracted to pheromone lures, so this is one tool in our favor for helping to narrow a search. I have known food quality consultants who would put a pheromone tap on a clipboard and simply walk up and down the aisles in supermarkets. They often would have the adult moths flying out of infested candy aisles or bulk food bins when they would stop for a minute or two in that aisle. I have seen candy bar vending machines with the adult moths resting inside, the result of infested candy bars in the machine.
I suppose if we consider where these moths came from originally it is possible that some adult moths simply flew in from the outside and began the infestation. They are so common that some of them must be flying around outside. But, I'll bet that it's far more likely that the original problem did come into this store in some infested product from another source. It's difficult and another thing to have to do, but all food products entering a store really should get inspected before it is accepted and place in storage. They may not be able to do such a thorough check that no moths can slip by them, but they also may be able to intercept some infested materials by checking inside boxes for larvae, holes in packages, silk webbing or fecal material, or other evidence that something is amiss.
I understand that with many suppliers of products it would be difficult for them to go to each and every one and ask to be allowed to inspect their stored product, and that is why this customer needs to at least make the effort to inspect on his own what is coming in. If you want to eliminate these moths once and for all it is going to take a huge effort on your part as well as the customer. Every area of the store needs to be carefully inspected for evidence of the moths, and this includes removing all packages of food, checking them carefully, and replacing them once you are sure there is no IMM in them. Spills must be cleaned up. Bulk foods need to be inspected and then stored in bins or containers that can be sealed to prevent the moths from entering.
Fogging is not going to affect this problem, nor would applications of contact insecticides along bases of shelves or walls. You may be able to kill some adult moths, but this will not affect the larvae living hidden within packages or food materials. One tool you might consider is one of the "mating disrupters", such as CideTrak. This is another kind of pheromone device, but it emits such a large amount of the mating pheromone into the air that the hope is that males cannot find females to mate with, and with luck you can break the cycle of new eggs being produced and the problem will more or less go away by itself. Better, of course, would be to find and dispose of the infested food materials so that they do not end up being sold to someone who objects to bugs in their food.
Mr. Pest Control
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Please note, Mr. Pest Control is answering questions supplied by PMP customers across North America. His answers are generated from industry and manufacturer-provided information. The answer may not be specific to the laws and regulations for your State, Province, Territory or Country. In addition, products mentioned may not be registered and or available in all areas. Always check with your local Univar office for specific information to your area. Always read and follow label directions.