Designing Indianmeal Moth Trapping Programs

Monitoring programs are a critical part of pest management in the food industry. While use of pheromone traps to monitor stored-product insect activity has been increasing, there is still considerable room for improvement in how these programs are conducted and how the information is used. “How many traps should be used?” is a commonly asked question about pheromone trapping programs. Unfortunately, this is not a simple question to answer. The number of traps should be based on information on pest ecology and behavior and facility characteristics; should meet monitoring program objectives and facility standards; and also should be cost effective. Another complicating factor is that it is not just the number of traps that is important, but where those traps are placed.

There are multiple factors to consider in determining the best number and placement of traps, and these factors may change over time. One approach to determining the best program for a given facility is to start off with a relatively high-density grid of traps and then use the monitoring results to refine and optimize the program.

I recently worked on a study with Frank Arthur and Michael Toews, “Distribution, Abundance, and Seasonal Patterns of Plodia interpunctella (Hübner) in a Commercial Food Storage Facility” (published in Journal of Stored Products Research, April 2013). In the study, we used the results of a pheromone trapping program for Indianmeal moths in a food distribution warehouse to determine how far the number of traps could be reduced while still providing accurate information on pest activity; we also looked at how much cost savings this would represent.

Manufacturers of pheromone traps and lures provide recommendations on trap density; however, data showing why these densities are best is not typically provided. For Indianmeal moth monitoring with diamond-shaped sticky traps, manufacturers recommend placing traps 26 to 49 feet (eight to 15 meters) apart in a grid pattern. The warehouse we used in this study was approximately 152,000 square feet (about 14,100 square meters), so manufacturer recommended trap numbers were between 60 and 239 traps. We placed 52 traps, which was close to the lower density recommendation. Our trap number and placement was determined based on providing even coverage and what we thought would be reasonable to service.

The cost of monitoring depends on the number of traps used and the fixed cost of traps and lures, as well as on how frequently traps are checked and/or replaced and how long it takes to identify and count the insects captured (this increases with increasing insect captures). The cost of monitoring also will depend on whether it is conducted by in-house personnel or contracted out to a pest control company. For our study which lasted about 2.5 years, we calculated the total cost at $5,974, which included fixed costs, time spent in facility, and time processing the traps; it did not include costs associated with data analysis, replacing lost traps, or travel. The estimated cost to conduct the same program using minimum and maximum recommended trap numbers would have ranged between $6,893 and $27,456. This is a considerable difference in cost, which would have to be weighed against additional benefits obtained from the higher number of traps.

Results of our monitoring programs showed seasonal and yearly variation in the levels of moth activity, but showed little pattern over time on where moths were captured. This pattern is consistent with what you would expect, due to the high mobility of moths, frequent movement of food material within a warehouse, and seasonal fluctuations in temperature.

We determined that for this insect and facility, the objective of the monitoring program should be to detect seasonal patterns in moth abundance using average moth capture rather than trying to detect a spatial pattern in captures. This information would be useful for guiding the timing and frequency of aerosol insecticide applications. Based on this objective, we wanted to then determine if the size of the monitoring program could be reduced while still detecting patterns of moth activity.

To make this determination, we wanted to find trap locations that were more consistent in capturing higher numbers of moths. To do this in a systematic way, we selected a threshold moth capture level of two moths per day (indicating a high level of moth activity) and identified trap locations that exceeded this threshold more than 30% of the time. In our study, 43 trap locations met these criteria in at least one year of the study, 16 locations in at least two years, and only five trap locations in all three years. The average moth capture if we had just used these reduced numbers of traps was then calculated, and we found that they gave equivalent results. This suggests that there was limited loss in information on trends in moth activity by reducing the monitoring program to these specific trap numbers and locations. Reducing the number of traps offered considerable economic benefits: our estimated monitoring costs would have been reduced by 17% with 43 trap locations and reduced by 69% with 16 trap locations. Five trap locations is probably too few traps for a facility this size, but would have reduced costs by 90%.

While the specific costs and results in terms of trap numbers presented here clearly only apply to this particular facility and insect species, the approach should be feasible in many facilities. This type of analysis should not be the sole factor in determining trap number and placement, but it can be a useful tool for developing cost effective and effective pheromone trapping programs. Cost savings could then be invested in other components of pest management such as inspection, sanitation, and structural modification.