Research from a team of US experts provides valuable insight into the practice of rodent bait and trap placement. Is it time to change our rodent management practices?
The ‘three lines of defence’ approach to rodent management is the traditional approach. This involves setting baits and traps inside the building (particularly the interior perimeter), along the exterior perimeter and if allowed along the fenceline. This three-tiered approach has long been considered best practice, but is it really the most efficient – and successful – approach?
Over the last 20 years, rodent management experts have been calling for an evaluation of this ‘one size fits all’ interval-based approach to setting traps and baits, especially at food facilities where rodent pressure is high. Placing bait stations or traps at set distances sounds good in theory, but this fails to take into account additional factors that affect bait uptake – food availability, environmental conditions, and accessibility, to name a few.
A team of US rodent experts including Dr Bobby Corrigan and academics from the New York State Integrated Pest Management Program at Cornell University studied the efficiency of traditional trap spacing over a period of nearly seven years. In their joint research paper, published in Journal of Stored Products in June 2021, the team looked at the number of trap catches and amount of bait consumed at 12 food handling locations across the US and Canada.1
Before looking at the research data, it is helpful to understand the origins of interval spacing practice. Devised in the 1940s, the strategy is based on estimates of mouse and rat foraging ranges.2 Put simply, house mice are known to travel between 5-10 metres when foraging. By placing devices at six-metre intervals along interior perimeter walls, foraging rodents would never be more than six metres from a device at any time, creating a protective barrier. The same philosophy was applied to exterior stations that were spaced further apart to account for rat foraging behaviour. Without testing or evaluating to determine if this approach effectively protects facilities from rodents, it was adopted by third-party auditing agencies and used to develop in-house management programs.
For more than 80 years, guidelines have remained relatively unchanged – despite advances in our understanding of rodent biology, behaviour and management. Interval spacing of devices remains the unchallenged norm. The question remains: does interval device spacing provide the best protection for customers?
To evaluate this question scientifically, the US research team worked with two pest management companies to record rodent activity at 12 food distribution centres. Sites ranged in size from 790 sqm to 18,400 sqm and all had a history of rodent activity. A list of characteristics was used to describe the area within 1.5 metres of each device, such as whether conditions were attractive to rodents – e.g. with food and water nearby – and structural features of the building that might affect rodent movements, such overhanging foliage and openings. For interior devices, the rate of trap capture was recorded; for exterior bait stations, the level of bait consumption was recorded. The evaluation period was 10-69 months, depending on data availability from each site.
Looking first at the results for interior devices, the data revealed a surprisingly low capture rate. The number of mice caught in a trap at any one time ranged from one to eight, but 85% of captures were of a single mouse. Most devices trapped mice only one time per year (Figure 1).
The percentage of devices that caught mice in a facility ranged from 13-91% with an average of 45%. This means, on average, less than half of the traps in a facility actually captured mice each year. The percentage of traps with two or more captures ranged from 0-83%, with an average of 30%.
The team discovered that several ecological and structural factors influenced whether or not a device would catch mice. Capture rate was higher for interior traps placed in a corner, which were shadowed during the day, on the south or west side perimeter wall, near a rodent-proof single door, or near a poured concrete wall.
Some of these findings are consistent with rodent biology. For example, corners and shadows offer protection for foraging mice, while south- and west-facing walls buffer against cold temperatures in winter months (north and east facing in the Southern Hemisphere). Higher captures near rodent-proof doors and poured concrete walls could be a response to the need for cover or escape routes in areas with no entry/exit points. In other words, rodents foraging near these pest-proof structures have no other options for cover and might enter traps in response to disturbance.
Support for this hypothesis comes from related results of decreased monthly capture for devices near a loading dock door with a non-pest-proof leveller, and near a corrugated wall with insulation. In these settings, rodents would have sufficient openings in which to hide or escape detection while foraging, therefore avoiding curiosity traps.
Taken together, these results justify the use of pest exclusion to seal openings as a method to not only prevent rodent entry, but enhance rodent management. Interestingly, devices near a warm mechanical room were associated with decreased rodent capture. Perhaps because devices were not placed close enough to the warm elements of these spaces.
Looking at the outside stations, rodenticide consumption data was available from four sites (73 bait stations), and included 2,769 observations. ‘No feeding’ accounted for 37% of observations, with minimal feeding of ‘one corner removed’ observed 19% of the time (Figure 2). Monthly bait consumption was higher for stations located on the west side of the building, and near unmaintained, dense vegetation. As with interior areas, in the Northern Hemisphere the west side of the building is associated with warmth during winter months, while dense vegetation provides cover for rodents to forage.
The results demonstrate that certain ecological and structural features of a facility are associated with higher trap capture on the interior, and increased bait consumption on the exterior. Considering that, on average, fewer than half of interior multi-catch devices caught a rodent, it seems that interval device spacing does not maximise rodent management at food distribution centres.
So where to from here? The research team offered their conclusions.
“Our results demonstrate that rodent management can be improved, and we therefore propose a paradigm shift towards assessment-based placement of devices. This approach can offer time and cost savings, enhance food safety by improving program efficacy and reduce environmental waste,” they said.
“Also, dynamic programs that rely on inspection and interpretation of evidence can reduce trap fatigue, a phenomenon where device captures decrease over time if traps remain stationary, especially for stable rodent populations. Assessment-based programs can also reduce technician fatigue, where service professionals become trap-checkers that open, clean and replace bait or glueboards without assessing the rodent problem or developing management approaches specific to that location.”
It makes sense for pest managers to put stations and traps where rodent activity is high and to remove them where activity is low. This would mean firstly determining the areas in the facility that would be most attractive to rodents. The use of activity mapping software to generate accurate activity reports can make light work of this task. Data entry can be manual, made easier by barcoding, or automated by utilising some of the new remote sensor technologies.
Economics of intervals: an example
To understand the benefits of assessment-based device placement, let’s take the example of a facility that has 50 interior multi-catch devices.
Based on the results of the study, 45% or 23 of the devices are likely to intercept rodents, leaving 27 devices untouched, but checked by a technician at each visit. These devices may be in a brightly lit area with heavy foot traffic, making them extremely unlikely to have rodent activity. Assuming that servicing each device takes two minutes and a service cost of $1.25 to $2.50, removing the 27 unused traps could result in a time savings of 54 minutes, and a service cost saving of $33.75 to $67.50.
Time saved on device-checking could be used to perform the often overlooked, proactive inspections into those hard-to-reach areas where new infestations can begin because they are out of sight, out of mind. Or it could be used to dig deeper for any conducive conditions that would justify additional control equipment.
Similar economic savings are expected for exterior rodent management, in addition to environmental benefits. In the study, 56% of the observations were of no feeding, or feeding on only one corner of the rodenticide. Yet bait is often replaced monthly, regardless of the amount consumed. Discarding one bait block every month from stations with only minor feeding would result in the disposal of 1,554 blocks from these four sites alone. The amount of bait sent to the landfill would increase if more than one block were used per bait station, and would double for sites that replace bait twice per month.
While the environmental benefits have not been estimated, savings in service time (3.5 minutes per device) and service cost ($3 to $5) can easily be calculated, with resources redirected toward assessment.
(Source: PCT Magazine)
“Sensor technology definitely has the potential to provide pest managers with more information about rodent activity at their accounts than they’ve ever had access to before,” commented Samuel Woods, Asia Pacific business manager for Bell Laboratories. “Interpreting this data effectively will allow pest managers to be more efficient with their programs, and to spend less time checking bait stations where there’s no activity, and more time solving their customer’s problems.
“iQ products powered by Bell Sensing Technologies, which will become available in Australia later in 2022, allow pest managers to use rodent monitoring technology at every account. Whether they choose bait stations, trapping, or a combination of both, the corresponding iQ products in combination with the easy to use Bell Sensing Technologies mobile app provide the pest manager with the knowledge of when and where rodents are travelling and the valuable efficiency of never checking an empty trap again.”
Once rodent activity has been assessed, the second step is to add bait stations or traps to these known activity areas and areas of likely rodent activity. During regular maintenance visits, reviewing the latest activity data will allow pest managers to either remove stations from areas of no activity or relocate them to areas of high activity.
To move to this radically different (yet evidence-based) approach requires the collection of data and the education of the customer. But with comprehensive activity reports, time can be saved by not emptying and refilling redundant stations. That time can be redirected toward inspection and assessment, with the superior placement delivering superior results. Comprehensive activity reports provide the evidence required to give the customer the confidence in your approach.
In the words of the study authors, “A true paradigm shift will take time for policies to change and for adoption of new practices. Pest professionals will play a vital role in accelerating that change by taking action now.”
More information on how to control rats and mice.
1 Frye, MJ, JL Gangloff-Kaufmann, RM Corrigan, H Hirsch, D Bondy. 2021. Assessment of factors influencing visitation to rodent management devices at food distribution centers. Journal of Stored Products Research 93: 101838.
2 Corrigan, RM, Rodent pest management, in Food Plant Sanitation, ed. by Hui YH, Bruinsma BL, Gorham JR, Nip W-K, Tong PS, and Ventresca P, Marcel Dekker, New York, NY, pp. 265-291 (2002).
Reworked article from Placed or Spaced? by Matt Frye, Jody Gangloff-Kaufmann, Bobby Corrigan, Hank Hirsch and Dusana Bondy. PCT Magazine, October 15, 2021.