Here, we introduce three methods for the physical control of pest rodents, four methods for counting their effectiveness against rodents, and the statistics of the effect of building a rodent-proof wall.
Rodent damage poses a significant threat to crops, human life, and health. Compared to chemical rodent control, such as placing poisonous baits, it is more economical and environmentally friendly to use physical methods, such as building a rodent-proof wall. This study introduces a method of physically controlling harmful rodents and four methods of calculating the effect of rodents control. To understand the controlling effect of the rodent-proof wall, an investigation was conducted on the Dongting Lake beach and corresponding farmland in the embankment in April and July 2012. Our findings illustrated that the density of the reed vole Microtus fortis in the farmland with rodent-proof walls was 0.52%, significantly lower than that in the farmland without rodent-proof walls (1.76%) after artificial trapping and drug extermination (χ2 = 3.900, P = 0.048). The density of M. fortis that had migrated into the farmland in dikes with a rodent-proof wall decreased by 98.53%, significantly higher than the decrease of density in dikes without a rodent-proof wall (86.61%) (χ2 = 11.060, P = 0.01). The results demonstrated the effectiveness of rodent-proof wall control. Therefore, building a rodent-proof wall should be advocated and vigorously promoted to prevent the migration of rodents into the Dongting Lake area and similar environments, as they cause harm.
Rodent damage is an important biological disaster that causes extensive damage to all aspects of human production and life1,2. In agriculture, rodent infestation of farmland damages crops3; in forestry, rodents eat tree seedlings, roots, bark, and plant seeds, leading to delayed forest regeneration and tree death, which in turn affects forest greening and sand fixation4; and in grasslands, rodents eat roots and seeds, leading to degradation of grassland vegetation and increased sanding, which affects the development of the grassland livestock industry5. In addition, rodents are hosts for many viruses, bacteria, and parasites that can seriously endanger human health6.
Dongting Lake, located in the northeastern region of Hunan Province, is an important water storage and flood-regulating lake in China7. It has many ecological functions, such as flood regulation and detention, biodiversity protection, and water resource supply8,9. In recent decades, there have been many rodent outbreaks in the Dongting Lake area, especially an outbreak of the reed vole Microtus fortis in 2007, which caused enormous economic losses10. During the dry season, M. fortis grows and breeds on the lake beach in the Dongting Lake area. As the water level in Dongting Lake rises during the summer flood season, the habitat of M. fortis shrinks, forcing it to migrate into the embankment by swimming, crossing the flood control embankment, and reaching nearby farmlands, causing great harm to agricultural production11,12. Chen et al. proposed a control measure for building a rodent-proof wall to block the migration pathway of M. fortis, based on the wave-retaining wall method jointly created by Jinpen Farm and Nanda Town in Yuanjiang City, both of which are located in Yiyang City, Hunan Province13,14. In dikes without rodent-proof walls, large numbers of M. fortis can cause devastating damage to crops during and after migration. Dikes without rodent-proof walls are typically manually trapped and drugged to exterminate rodents during and after they enter the farmland. In the case of dikes with rodent-proof walls, many rodents remain outside the dikes during M. fortis outbreaks. Thus, many trapping and elimination operations are carried out outside dikes; generally, farmlands do not need to implement chemical drugs or artificial trapping. This approach can significantly reduce the density of vermin without causing serious harm to farmland crops. Conventional rodent drug prevention methods cannot achieve the expected effects, and there are hidden dangers associated with environmental pollution and human and animal safety15. Considering the characteristics that allow rodents to easily break out and cause disaster, the following protocol introduces three physical rodent control methods, including a permanent rodent-proof wall and two kinds of temporary walls, and presents four statistical methods to measure rodent control effect, providing a scientific basis for rodent control. Instead of the traditional poisonous bait, the rodent-proof wall effectively protects the environment and safeguards the health of humans and animals; thus, it is a more effective and environmentally friendly control method that should be advocated and vigorously promoted.
All animal experiments were approved by the Ethics Committee of the Institute of Subtropical Agriculture, Chinese Academy of Sciences.
1. Construction of rodent-proof wall
2. Methods of efficiency statistics
3. Statistical analysis
To determine the control effect of the rodent-proof wall, surveys were conducted before and after the water rose in April and July 2012, respectively, on the lake beach and corresponding diked farmland15. The survey sites were located in the Dongting Lake area of Hunan Province, namely, the lake beach outside Matangyuan in Yueyang County (29°14.5′ N; 113°03.2′ E), Beizhouzi Town in Datong Lake District (29°10.1′ N; 112°47.7′ E), Shuangfeng Dike in Nanda Town in Yuanjiang City (29°1.3′ N; 112°45.2′ E), and Muping Lake outside Munan Village Dike in Chuangyeyuan Nanzui Town in Yuanjiang City (28°59.6′ N; 112°15.1′ E). The polder in Beizhouzi and Nanda towns built rodent-proof walls, whereas those in Matangyuan and Chuangyeyuan did not.
In April 2012, a total of 815 traps were placed in the lake beach habitats of the four survey sites, and 258 animals were captured, of which 248 could be identified to the species level: 197 M. fortis, 41 Apodemus agrarius, 7 Rattus norvegicus and 3 Suncus murinus (Table 1)15. From the remaining 10 animals, only parts of their bodies, such as the tail, feet, hair, and blood, were captured; thus, the species could not be identified. In July 2012, 1141 tongs were placed at 4 survey sites in farmland habitats, and 59 animals were captured, of which 54 were identified: 38 A. agrarius, 13 M. fortis, and 5 R. norvegicus. For the remaining five animals, only parts of their bodies, such as the tail, feet, hair, and blood, were captured; thus, the species could not be identified. The farmland was dominated by A. agrarius and M. fortis, which accounted for 70.37% and 24.07% of the species composition, respectively.
The capture results for the dikes with and without rodent-proof walls are listed in Table 2. Owing to the low population of M. fortis on the lake beach of Muping Lake, the density of M. fortis on the outer lake beach without a rodent-proof wall was relatively low. However, the density of M. fortis in the corresponding farmland in July was higher at 1.76%, whereas that of M. fortis with a rodent-proof wall was only 0.52%. In terms of the absolute values, there was also a significant difference (χ2 = 3.900, P = 0.048); the density of M. fortis in farmland with a rodent-proof wall was significantly lower.
Considering the density of M. fortis at the lake beach as the base, the decrease in M. fortis density in the farmland of the corresponding dike was calculated (Table 3)15. The density of M. fortis in the dike with the rodent-proof wall was further reduced. The average decrease in the density of M. fortis in the dike without a rodent-proof wall was 86.61%, whereas that in the dike with the wall was significantly higher at 98.53% (χ2 = 11.060, P = 0.01). In the Nanda Town Shuangfeng polder, no M. fortis was captured in the farmland, despite the density of the lake beach reaching 29.61% (Table 1)15. This suggests that the rodent-proof wall protects against and controls rodents.
Figure 1: Rodent-proof wall. Build the wave-retaining wall 0.5 m higher than the embankment surface. Smooth the wall surface on the lakeside with cement, and add a flat plate slightly wider than the wall to the top such that it extends 8 cm, similar to a tongue. Please click here to view a larger version of this figure.
Figure 2: Rodent-proof trench. The ditch is 0.5 m deep, slightly wider than the gap of the wave-retaining wall. Usually, the trench is filled with soil or covered with a thin cement board to facilitate the passage of pedestrians and vehicles. During the flood season, the thin cement board is removed, and the soil in the trench is cleared, thereby completely blocking the rodents' migration pathway. Please click here to view a larger version of this figure.
Figure 3: Buried pots barrier method. Fences are erected along a dike; the baffle plate can be composed of fiberboard, plastic film, or wood board and is supported by timber piles. The plate fence is buried 5-10 cm into the soil to a height of 0.5 m. The deep pots are buried between fixed fences at 50 m intervals. The pots are 80 cm deep and 60 cm in diameter and buried in the soil immediately next to the baffle plate, with the mouth of the pots flushing with the ground. Rodents then approach the dike, walk along the fences, and are channeled into the pots. Finally, the pots are dredged to remove the rodents. Please click here to view a larger version of this figure.
Site | Habits | Number of traps | Number of animals | Total capture rate (%) | Capture rate for each species (%) | |||
Rattus norvegicus | Apodemus agrarius | Microtus fortis | Suncus murinus | |||||
Matang polder | Beach | 178 | 61+1 | 34.83 | 0 | 3.93(7) | 29.78(53) | 0.56(1) |
Farmland | 270 | 15 | 5.56 | 0.37(1) | 2.22(6) | 2.96(8) | 0 | |
Chuangye polder | Beach | 233 | 10 | 4.29 | 0 | 3.86(9) | 0.43(1) | 0 |
Farmland | 297 | 12+2 | 4.71 | 0.34(1) | 3.03(9) | 0.67(2) | 0 | |
Beizhouzi | Beach | 198 | 101+1 | 51.51 | 1.01(2) | 7.58(15) | 41.41(82) | 1.01(2) |
Farmland | 290 | 27+2 | 10 | 0.34(1) | 7.93(23) | 1.03(3) | 0 | |
Nanda shuangfeng |
Beach | 206 | 76+8 | 40.78 | 2.43(5) | 4.85(10) | 29.61(61) | 0 |
Farmland | 284 | 0+1 | 0.35 | 0 | 0 | 0 | 0 |
Table 1: Capture of rodents at each investigation site in April and July 2012. Values after the plus sign indicate the number of captures for species that could not be identified. Values inside the plus sign indicate the number of captures for each species.
Rodent-proof wall | Habits | Number of traps | Number of animals | Total capture rate (%) | Capture rate for each species (%) | |||
Rattus norvegicus | Apodemus agrarius | Microtus fortis | Suncus murinus | |||||
Without rodent-proof wall | Beach | 411 | 71+1 | 17.52 | 0 | 3.89(16) | 13.14(54) | 0.24(1) |
Farmland | 567 | 27+1 | 4.94 | 0.35(2) | 2.65(15) | 1.76(10) | 0 | |
With rodent-proof wall | Beach | 404 | 177+9 | 46.04 | 1.73(7) | 6.19(25) | 35.40(143) | 0.50(2) |
Farmland | 574 | 27+3 | 5.23 | 0.17(1) | 4.01(23) | 0.52(3) | 0 |
Table 2: Capture of rodents on the dike with and without rodent-proof wall. Values after the plus sign indicate the number of captures for species that could not be identified. Values inside the plus sign indicated the number of captures for each species.
Rodent-proof wall | Site | Capture rate of Microtus fortis (%) | Decrease rate of population density (%) | |
Beach | Farmland | |||
Without rodent-proof wall | Matang polder | 29.78 | 2.96 | 90.06 |
Chuangye polder | 0.43 | 0.67 | 0.00* | |
With rodent-proof wall | Beizhouzi | 41.41 | 1.03 | 97.52 |
Nandashuangfeng | 29.61 | 0 | 100 |
Table 3: Decrease population density rate in farmland and adjacent beaches after Microtus fortis immigrated into farmland. The symbol * indicates that the capture rate in farmland was higher than that on the beach, which may have resulted from the low base; therefore, the decrease rate was calculated as 0.00%.
There are several critical steps in the protocol. The width of the tongue-shaped flat plate of the rodent-proof wall should be sufficiently wide, and the height of the wall should be set such that rodents in the area cannot cross it. When wave-retaining walls have gaps leading to the beach, the depth of the rodent-proof trench should be set to a depth that rodents cannot climb, and the width of the ditch should be set to a distance that rodents cannot cross. The height of the baffle plate and pots in the buried-pot barrier method should be set to a height that rodents cannot cross. When an outbreak of rodents occurs in an area, the rodents in the pots should be cleaned out regularly to keep the pots clean and prevent the rodents from jumping out of them.
Assessing the effectiveness of rodent control is indispensable and important in evaluating the performance of such controls and summarizing the experience17. When investigating the effects of rodent control, the conditions before and after- rodent control must be as similar as possible. Methods are needed to set up a control area (areas without rodent control) to further calculate the corrected rodent control rate and evaluate the rodent control effect more objectively. The snap-trap method is suitable for small rodents, which mostly exhibit nocturnal activity18. The snap-trap method was used before and after rat extermination using the same size of the rat trap, with the same size of food bait, and the same method as the cloth clip. The snap-trap method is simple, has a wide range of applications, is not subject to seasonal restrictions, and can be used as a test material. However, several factors affect the capture rate, for example, the abundance of outside food and whether other animals, such as insects and ants, ingest the bait. In addition, a mouse trap can catch only one mouse; therefore, the capture rate is relatively low17.
The bait consumption method is mainly based on rodents stealing the bait to observe the degree of reduction in their population19. The water content of the bait decreases in the environment. To calculate bait consumption more accurately, it was necessary to create a control group for the natural reduction of bait water to correct bait consumption. The bait used should be different from the poisonous bait to avoid affecting the bait consumption rate in the rodent extermination effect survey. Poisonous baits are mostly prepared using grains, with sweet potato pieces often being used. Generally, they are coarse or fine depending on their specific practices for different purposes. In the former, the number of grains was fixed for each bait pile, and the piles of bait that were stolen and dragged for food (without counting the number of stolen grains or those dragged for food) were listed as the number of piles eaten. From the total number of piles laid and the total number of piles eaten, the theft rate was calculated as an indicator of rodent density; the latter, rather than comparing the lure of two baits to rodents, is a more refined approach. Briefly, each bait pile was quantified, and the consumption rate was calculated after a certain period; however, the bait can also be moved and eaten by cockroaches or other insects. We prepared larger bait pieces and focused on the timely recovery of the bait to prevent its consumption by poultry. In addition, the weather conditions before and after baiting should be the same.
The excavation hole method can be used in any area where a rodent hole is found. The excavation hole method saves labor. However, some rodents (e.g., weasels) can dig more than one hole. In the field, a detailed check on the number of rodent holes in a certain area was conducted to reduce the impact of abandoned holes. Soil, dry dung, dry grass, or twigs were then used to tightly block all the holes. This has two purposes: to prevent beetles, lizards, and snails from moving in and out of the open hole and to assist in determining whether the hole was dug by a rodent inside or outside the hole.
The use of physical methods to control the migration of rodents has improved the economic and ecological benefits over chemical rodent control. The rodent-proof wall replaces traditional poisonous bait to prevent rodents, effectively protecting the environment and ensuring human and animal safety15. In addition, the rodent-proof wall is a permanent barrier to prevent rodents from entering the farmland, based on the original "wave-retaining wall" on the dike around Dongting Lake, and according to the characteristics of the migratory hazards of the rodents and their weak climbing ability. The rodent-proof wall is suitable for rodents with migratory habits. The rodent-proof wall is suitable for areas where rodents migrate from one habitat to another, and after migration, it will cause harm to an area. This method of constructing rodent-proof walls could also be applied in other areas to control rodent infestations, for example, where an outbreak of rodent infestation occurs in a single area, or an area of conservation value needs to be protected from invasion by pest rodents. If frequent outbreaks of rodent infestation occur in an area, permanent rodent-proof walls made of cement can be constructed. It requires some time to build a rodent-proof wall; however, once built, the wall provides long-term and stable protection. The cost of building a rodent-proof wall in conjunction with existing works (e.g., wave-retaining walls) is low. Finally, for temporary rodent infestation outbreaks, it is possible to build temporary rodent-proof walls. Temporary rodent-proof walls can be constructed of plastic, fiber, or materials other than cement to reduce their building costs.
The authors have nothing to disclose.
This work was supported by the National Natural Science Foundation of China (U20A20118) and the Open Fund of the Hunan Engineering Research Center of the Ecological Environment Institute Monitoring and Disaster Prevention and Mitigation Technology in Dongting Lake (2023-DTH-04).
Snap traps | Guixi Mousing Tool Factory, Jiangxi, China | large-sized | 150 mm × 80 mm |
SPSS | IBM | version 16.0 |