The Indian meal moth (IMM) is one of the most common stored product pests encountered by pest professionals. This insect is what we term "cosmopolitan" in distribution, meaning it is "everywhere."
Most of the time this pest is easily controlled using a variety of pesticides in a wide variety of formulations. As long as we find the source the success rate when servicing accounts with Indian meal moths is about 90 percent. However, there are some cases that are truly baffling in nature and really take some time, effort, knowledge and skill. Here is one such case:
A CAUSE-AND-EFFECT CASE STUDY. I refer to the following as the "Why can’t you get rid of these *^$*@)# moths from my expensive house" case.
The message came to me in a round about way. The message was: "Give this current customer a call and get rid of the moths."
After speaking with the technician and supervisor who had been trying to get rid of the moths for several months, I called and set up an appointment to take a look.
The customer, whom I will refer to as Mrs. Golf, had dutifully collected samples of these "horrid bugs" to show me. When I asked Mrs. Golf where she had collected these pests she replied, "In every room." The time of the year was early June.
Now, we know that most of the time IMMs are found in stored products ranging from damaged bird seed to dog food to many other sources. And we also know that customers often exaggerate the scale, numbers and locations of where the pests are found. I have found that most customers will not out-and-out lie to us, but rather exaggerate the extent of the problem.
USUAL INSPECTION AREAS. The necessary inspection of the kitchen, pantry and other storage areas showed no visible insects in any stage. As a matter of fact, the house was in perfect order with nothing out of place anywhere.
Since the "insects were everywhere" it was decided that placement of pheromone traps would help us narrow this down. Eight traps were placed in various locations on all three levels of the house. A second appointment was agreed upon for the following week. The next week showed a surprising number (50+) of insects in several areas of the house. IMMs were found in the kitchen (as expected); in the living room – in numbers about equal to those in the kitchen; and in the basement’s traps, where numbers were significant, but not as high.
At this time treatment was also being done with crack and crevice applications of the Whitmire PT line, including contact kill as well as residual aerosol formulations.
Traps were replaced and more were concentrated at the rear of the house and in the kitchen and living room. At this time the attic was treated using a boric acid dust just to make sure that area was not a potential source.
During the next week I was repeatedly reminded that I was responsible for the eradication of these pests and that Mr. Golf was increasingly frustrated with our inability to get rid of these pests.
On my third visit I found traps that were placed under the sink and under a JenAire unit completely full. Also full was a trap near the fireplace and another on the exterior wall. After locating the vent for the JenAire cooking appliance I placed a trap on the outside of the house (inside a rodent bait station) as well as one in the fireplace.
The next week showed that these traps were so full of IMMs that we were almost in a control stage of pheromone trapping. At this time, due to the number of IMMs in the stations it was decided these traps would be placed on the exterior of the house by the kitchen and living room.
The next week showed that these exterior traps were also loaded, but the traps on the interior had fewer IMMs. So far no larval or pupa cases had been discovered.
Upon inspection of the home’s exterior a large number of chipmunk burrows or runs were discovered. In the front yard, there were a number of mature white pine trees with a lot pine cones scattered around the ground. I thought to myself that pine cones contain pine nuts — a possible food source for a number of animals and arthropods — but could this be a part of the problem?
We set up a chipmunk trapping program (22 of the little devils were eventually caught) and dusted the burrows using an appropriate insecticide dust. After two weeks the numbers of IMMs in the traps were down by 75% and after continued treatment using a variety of methods we eliminated the IMM infestation inside of the house.
Mr. and Mrs. Golf were not impressed, instead believing that this outcome should have been accomplished several months earlier.
LESSON LEARNED. Chipmunks storing seeds (of any kind) will process or "break up" the seed, thus providing some stored product pests a viable food source. Indian meal moths had found this food and the larval migration away from food sources to other viable locations and had moved into the house through cracks and crevices in the foundation. Don’t go in with blinders on because solutions are not always as apparent as we would like them to be. You just have to do your homework, pause and think about "cause and effect," not just repeatedly applying pesticides because that is what you have done in the past.
The author is a pest management specialist with Franklin Pest Solutions, Michigan City, Ind., and can be contacted at firstname.lastname@example.org.