Better Bait 'Take'

Mice, as we have reported on more than one occasion, don’t necessarily enter bait stations. As such, that can make getting a “bait take” particularly problematic. New research from Purdue University provides some pointers on how rodents can be encouraged to enter into bait boxes.

Very little research has been done to evaluate the efficacy of mouse bait stations, the theory being that, because mice are extremely curious, they tend to investigate new objects. Position them carefully, in areas of high mouse activity, at entry points, and so on and all you have to do is wait for the bait to be taken.

The goal for the research by Dr. Grzegorz Buczkowski from the Center for Urban and Industrial Pest Management, Purdue University, was to test and develop more efficient techniques for attracting and catching mice. In addition to studying mouse bait stations, the work also looked at multiple catch traps.

Buczkowski explains: “We know that chemical signals contained within mouse feces and urine are extremely important in mouse communication, so we wanted to explore whether urine and feces could be used to ‘jump start’ traps and bait stations. We also hypothesized that surface texture might affect mouse entry into bait stations, so we set out to test a variety of materials and textures other than those currently available on the market. Finally, we wanted to test the theory that predator odor from rats would be repellent to mice and put them off entering bait stations and traps.”

With these three objectives in mind, a study site had to be found — and it needed to have plenty of mice. A commercial pig farm in West Lafayette, Ind., was identified. It had a large and stable house mouse population. The mice were concentrated around feed preparation areas, grain storage silos and manure pits under the pigpens. All of the buildings were in poor condition and provided easy access. The farm also offered the mice an unlimited supply of food and water, ideal nesting conditions and plenty of harborage.

“The farm was inspected for mouse activity two weeks before the start of the trial,” Buczkowski said. “Visual inspections identified optimal test sites, i.e., areas with visible mouse damage, high concentration of droppings and urine stains, sebum trails along walls, mouse nests, and actively foraging mice.”

OBJECTIVE 1:

‘JUMP-STARTING’ THE BAIT STATION.

Forty Bell Protecta mouse bait stations were used across four different buildings. Within each building, half of the devices were provided with 25 mouse fecal pellets freshly collected from within the building the station was to be located. These were scattered throughout the bottom of the device. The other half received no fecal pellets. The stations were baited with Bell Laboratories’ non-toxic rodent monitoring bait, Detex Blox. The efficacy of the bait stations was determined by the amount of Detex consumed within a 24-hour period. Tracking was used as a secondary assessment method. This consisted of placing two tracking pads next to the station and checking the pads for signs of rodent tracks after 24 hours.

Results. Adding fecal pellets significantly increased mouse activity inside the bait stations.

Mean bait consumption in stations provided with mouse droppings was 89 percent and significantly higher than bait consumption in stations not provided with mouse droppings (78 percent). Similarly, tracking activity around stations with fecal pellets was 81 percent vs. 65 percent for those without fecal pellets.

The addition of fecal pellets in multiple catch traps, however, had no effect. The researchers believe this may be due to the way the two devices are constructed. Bait stations are an open design so mouse droppings are easily detected by other mice. The presence of fecal droppings indicates areas where food may be present and signifies areas that have been visited by other mice and are therefore likely to be secure.

One option for increasing the efficacy of bait stations and traps may be to simply put the devices in places where mouse droppings are already present. Added droppings also might be more effective placed outside the devices where they can be readily detected by the mice.

Another management option to consider is the pre-conditioning of new devices. Brand-new devices that have never been used in the field lack mouse-specific odors and might even be repellent if they contain chemicals related to the manufacturing process (e.g., odors of paint, plastics or glue). Pre-conditioning new devices would help eliminate such odors and would make the devices more attractive by providing mouse-specific odors from mouse feces, mouse urine and other sources such as hair and sebum.

Interesting Findings. Rodent expert and PEST Technical Advisory Board member John Charlton commented: “These findings are interesting. We have long been aware of the importance of scent in the movement of mice and the benefit of placing baits in locations regularly used by mice. The effect of territorial marking by dominant mice may need to be considered as a factor in the use of bait boxes by mice from different groups. I suspect, however, that the placement of mouse droppings in, or around, bait stations would not be an option in food premises.

“The results should be of interest to operators who may be tempted to clean bait boxes,” Charlton added. “In some cases, chemical cleaners are used in order to demonstrate a ‘premier’ service to customers. The outside of the bait box should be kept presentable but the ‘dirty’ inside may be considered a benefit; on condition the bait remains palatable.

“The pig farm used as a trial site has a large population of mice — a necessity when running a trial. On many sites we deal with the number of mice is low — therefore the competition for feeding sites may be less. We are however aware of the use of urine markers in these small populations which results in regular re-distribution around large sites,” Charlton concluded.

OBJECTIVE 2:

DO SURFACE TEXTURES MATTER?

Bait stations are typically made of smooth, hard surfaces such as metal or molded plastic. To assess whether texture matters, three different materials were tested: cardboard, Masonite (a type of hardboard) and plywood. The adapted devices were all placed in areas of high mouse activity.

Results. Modified bait stations did not attract significantly more mice. They also had other limitations as Buczkowski explains: “One issue was low durability and susceptibility to moisture. All three materials are relatively soft and susceptible to damage by moisture, both from air humidity and mouse urine. Devices used for mouse control need to be durable. Metal and molded plastic meet this criteria and appear to be the best options for use in devices for mouse control.”

“Another problem with using softer materials is that they are easily damaged by mice,” he added. “All three materials tested were frequently shredded and used as nesting material.”

OBJECTIVE 3:

PREDATOR ODOR IMPACT

Rats are known predators of mice and the two don’t typically overlap. To expose the bait stations to rat odor the devices were placed inside a cage containing adult male and female Norway rats for 48 hours. The devices were randomly assigned to various locations throughout the test buildings and were placed in areas of high mouse activity.

Results. The results demonstrated that bait stations contaminated with rat odor significantly reduced mouse activity. However, the presence of rat odors did not completely prevent the mice from entering the bait stations. The researchers concluded that the biological importance of such effects is probably low and not important for practical rodent management.