Pest fencing or pest trapping: A bio‐economic analysis of cost‐effectiveness

Scofield et al. discredited the utility of pest‐exclusion fences for restoring biodiversity partly on the grounds of unquantified costs and benefits. We estimated the discounted costs of mammal exclusion fences, semi‐permeable (‘leaky’) fences and trapping, over 50 years and adjusted costs by their observed effectiveness at reducing mammalian predator abundance. We modelled data from two large predator management programmes operated by the New Zealand Department of Conservation. Using typical baseline costs and predator control efficacies (scale 0 to 1), the model predicted that an exclusion fence (efficacy 1.0) is the cheapest and most cost‐effective option for areas below about 1 ha, a leaky fence (efficacy 0.9) is most cost‐effective for 1–219 ha, and trapping (efficacy 0.6, based on 0.2 traps per hectare and a 1500‐m buffer to reduce predator reinvasion) for areas above 219 ha. This ranking was insensitive to adjustments in efficacy, but reducing efficacy of leaky fences to 0.8 or increasing trapping efficacy to 0.7 reduced the cost‐effective range of leaky fences by about 90 ha. Reducing trap maintenance costs from $300 to $100 per trap per year (e.g. using long‐life lures), or reducing trap buffer widths to 500 m, significantly elevated trapping as the most cost‐effective method for areas greater than 11–15 ha. These results were largely consistent with an ecological measure of effectiveness based on observed rates of recovery of two indigenous skink species inside exclusion fences or with trapping. The results support criticisms that exclusion fences are generally not cost‐effective, but highlight the value of considering cheaper leaky designs for small‐ to medium‐sized areas. Because this study is based largely on reductions in predator abundance, it has general application to broader biodiversity protection interests, but not to indigenous species that are highly sensitive to predation and only ever adequately protected on the mainland by exclusion fences.     

Standardized capture rates of the endangered American burying beetle, Nicrophorus americanus Olivier (Coleoptera: Silphidae) using different trap protocols

The U.S. Fish and Wildlife Service has adopted two different pitfall trap protocols to survey the endangered American burying beetle, Nicrophorus americanus. One protocol uses a transect of eight pitfall traps that prohibit bait contact over the course of three trap nights. The other protocol uses buckets that allow for bait contact over a five night trapping period. A trap night is defined as one trap open for one night, and the transect protocol has historically been calculated as eight trap nights per calendar night while; the bucket protocol has been calculated as one trap night per calendar night. This study examined the effectiveness of each protocol based on the number of beetles (Nicrophorus spp.) captured per trap night (BTN) in field and laboratory trials. When each transect was considered as a single trap instead of eight separate traps, no significant difference in BTN was detected between the protocols in any year. Laboratory trials were conducted using Nicrophorus marginatus to determine differences in capture efficiency based on protocol, time after release, and feeding status. The proportion of beetles captured after 5 days was greater when compared to 3 days for either protocol. Our results indicate that cup transects used to sample the American burying beetle should be considered as a single trap when calculating trap night and that the use of five trap nights rather than three would increase the likelihood of capturing beetles.     

Evaluation of trap designs and food attractants for trapping Eucryptorrhynchus scrobiculatus (Coleoptera: Curculionidae)*

Eucryptorrhynchus scrobiculatus (Motschulsky) is a serious pest of tree of heaven, Ailanthus altissima (Mill.) Swingle in China. Laboratory choice tests were conducted to compare attractiveness of vinegar, ethanol, apple juice, the vinegar-ethanol mixture (VE), vinegar-apple mixture (VA), ethanol-apple mixture (EA) and vinegar-ethanol-apple mixture (VEA) to E. scrobiculatus. VEA showed significantly higher attractiveness to E. scrobiculatus than vinegar, ethanol, apple juice alone, VE, VA or EA. The field experiments were conducted to evaluate the efficiency of commercial pitfall traps baited with different ratios of VEA (Apple: VE, m:m) for trapping E. scrobiculatus. Field evaluations showed that the number of marked and wild E. scrobiculatus in traps baited with the VEA (Apple: VE, 30:70 ratio, m:m) was significantly higher than traps baited with other ratios of VEA. Further testing of four types of trap baited with this VEA (Apple: VE, 30:70 ratio, m:m) indicated that captures in homemade pitfall trap design were significantly higher than in any other trap design (commercial pitfall traps, cross-vane versus traps and six-unit-funnel traps). The results demonstrated that homemade pitfall traps baited with the VEA (Apple: VE, 30:70 ratio, m:m) have potential for E. scrobiculatus monitoring.     

Pitfall vs fence traps in feeding efficiency of antlion larvae

Larvae of pit-building antlions are expected to be more efficient at capturing prey than those of non-pit-builders. To test this prediction, feeding behaviors were compared in the same experimental conditions among pit-building Baliga micans and Myrmeleon bore, and non-pit-building Distoleon contubernalis. The number of prey eaten did not differ between species. D. contubernalis larvae used the walls of the experimental chamber as fence traps to capture prey. In the field, they were also found near edges of natural barriers, such as rocks, stones, tree roots, and plant stems. Artificial pitfall traps captured more arthropods near the edges of fences than farther from them. Larvae of the two pit-building species were located in the central part of the experimental chamber. In their natural habitats, the number of arthropods captured by artificial pitfall traps increased with pit size; thus, larger pits may be more efficient for capturing prey. In conclusion, pit-building and non-pit-building antlion larvae are both efficient hunters; the former hunt efficiently by making larger pitfall traps, and the latter do so by waiting for prey at the edge of the natural fences along which arthropods walk.     

Too hot to handle? Balancing increased trapability with capture mortality in hot weather pitfall trapping

Trapping at air temperatures close to, or exceeding, critical thermal maxima is important for comprehensive sampling of vertebrate assemblages and collection of sufficient data for impact assessment. However, pitfall trapping on hot days also potentially exposes trapped animals to stress or death through overheating or desiccation. We investigate causes of mortality from 14 305 captures over a 22‐year pitfall trap study in arid South Australia and compared mortality rates with maximum temperatures, solar radiation and rainfall. Overall mortality rate was 3.2% with chewing by rodents and handling accidents the most influential cause of death recorded. The highest mortality rates were experienced by the tiny skink, Lerista labialis, which was difficult to detect in traps each day and hence problematic to assess the effect of weather variables on capture mortality. For all other abundant species, high maximum temperature was only a significant explanatory variable for increased death rates of the house mouse Mus domesticus, and increased solar radiation was positively related to capture mortality for the house mouse, the frog Neobatrachus sudelli and the small skink Ctenotus schomburgkii. However, capture rates for these taxa and eight other common species would have been significantly lower if trapping did not occur on days of 40 °C or more. We conclude that trapping in hot weather is both desirable and justifiable and suggest techniques for further reducing mortality rates in pitfall studies.     

Trapping and marking terrestrial mammals for research: integrating ethics, performance criteria, techniques, and common sense

We propose that researchers integrate ethics, performance criteria, techniques, and common sense when developing research trapping programs and in which members of institutional animal care and use committees address these topics when evaluating research protocols. To ask questions about ethics is in the best tradition of science, and researchers must be familiar with codes of ethics and guidelines for research published by professional societies. Researchers should always work to improve research methods and to decrease the effects on research animals, if for no other reason than to minimize the chances that the methods influence the animals' behavior in ways that affect research results. Traps used in research should meet performance criteria that address state-of-the-art trapping technology and that optimize animal welfare conditions within the context of the research. The proposal includes the following criteria for traps used in research: As Criterion I, killing-traps should render >/= 70% of animals caught irreversibly unconscious in /= 70% of animals with 相似文献   

Evaluating sampling strategies for enzootic Venezuelan equine encephalitis virus vectors in Florida and Panama

Determining effective sampling methods for mosquitoes are among the first objectives in elucidating transmission cycles of vector-borne zoonotic disease, as the effectiveness of sampling methods can differ based on species, location, and physiological state. The Spissipes section of the subgenus Melanoconion of Culex represents an understudied group of mosquitoes which transmit Venezuelan equine encephalitis viruses (VEEV) in the Western Hemisphere. The objective of this study was to determine effective collection methods that target both blood-engorged and non-engorged females of the Spissipes section of Culex subgenus Melanoconion to test the hypothesis that favorable trapping methods differ between species and by physiological status within a species. Mosquitoes were collected using two commercially available traps, (CDC-light trap and BG-Sentinel trap), two novel passive traps (a novel mosquito drift fence and pop-up resting shelters), and two novel aspirators, (a small-diameter aspirator and a large-diameter aspirator) in Darién, Panama, and Florida, USA. The total number of female mosquitoes collected for each species was compared using rarefaction curves and diversity metrics. We also compared the utility of each trap for collecting total females and blood-engorged females of four Spissipes section mosquito species in Florida and Darién. In Darién, it was found that both blood-engorged and unfed females of Cx. pedroi were most effectively collected using the mosquito drift fence at 57.6% and 61.7% respectively. In contrast, the most unfed Cx. spissipes were collected using the mosquito drift fence (40.7%) while blood-engorged females were collected effectively by pop-up resting shelters (42.3%). In Florida, the best sampling technique for the collection of blood-engorged Cx. panocossa was the large diameter aspirator at 41.9%, while the best trap for collecting Cx. cedecei was the pop-up resting shelter at 45.9%. For unfed female Spissipes section mosquitoes in Florida, the CDC light trap with CO₂ collected 84.5% and 98.3% of Cx. cedecei and Cx. panocossa respectively in Florida. Rarefaction analysis, and both the Shannon and Simpsons diversity indices all demonstrated that the mosquito drift fence was capable of collecting the greatest diversity of mosquito species regardless of location. The finding that the proportions of unfed and blood-engorged mosquitoes collected by traps differed both among and between species has implications for how studies of VEEV vectors will be carried out in future investigations. In Florida a combination of pop-up resting shelters and use of a large-diameter aspirator would be optimal for the collection of both VEEV vectors for host-use studies. Results demonstrate that traps can be constructed from common materials to collect mosquitoes for VEEV vector studies and could be assessed for their utilization in vectors of other systems as well. Unfortunately, no single method was effective for capturing all species and physiological states, highlighting a particular need for assessing trap utility for target species of a study.     

The relative efficiency of two commercial live-traps for small mammals

Data obtained from live-trapping a population of field voles, Microtus agrestis, over a seven-month period was used to compare the trapping efficiencies of the Longworth and the Ugglan Mouse Special traps. The Ugglan Mouse Special is a cheaper alternative that is widely used in Scandinavia. Biases in the sex or age of captured animals were the same for both types of trap and the total numbers of captures were similar. There was no evidence that individual animals were more likely to be captured in the same type of trap at each capture session. We conclude that the Ugglan Mouse Special trap is a practical alternative to the Longworth trap for studies of small mammals by capture-mark-recapture techniques.     

Multi-species predator eradication within a predator-proof fence at Ka‘ena Point, Hawai‘i

Ka‘ena Point Natural Area Reserve on O‘ahu hosts one of the largest seabird colonies in the main Hawaiian Islands and supports three species of endangered plants. In order to stop chronic predation by invasive alien mammals on native species, a peninsula-style predator-proof fence was constructed around a 20-ha portion of the reserve in 2011. Multi-species predator removal efforts began upon fence completion; diphacinone poison in bait boxes spaced 25 m apart was used to remove black rats, house mice, and small Indian mongooses. House mice also were removed with multiple-catch live traps spaced 12.5 m apart. Feral cats were removed with padded leg-hold traps. Feral cats and mongooses were eradicated in 1 month, black rats were eradicated in 2.5 months, and house mice were eradicated in about 9 months. Since eradication, incursions of cats and mongoose have been rare (1/7.2 months), but incursion frequency has been higher for black rats (1/56 days) and house mice (1/36–47 days). Buffer predator control was conducted to limit predator access and prevent reinvasion around the fence ends along the shoreline. Even with the high initial fence cost and ongoing predator incursion management, this method is expected to become more cost effective than previous predator control efforts after 16 years. Record numbers of Wedge-tailed shearwaters and Laysan albatrosses have fledged from the reserve after predator eradication, and regeneration of native plants and invertebrates is being observed. With careful planning and persistence, predator fences can be a cost-effective method of protecting natural resources, and multiple species of predators can be eradicated with traps and first-generation anti-coagulents.     

Optimization of a Trap for Tuta absoluta Meyrick (Lepidoptera: Gelechiidae) and Trials to Determine the Effectiveness of Mass Trapping

Management of the South American tomato leafminer, Tuta absoluta Meyrick, with insecticides has led to the widespread development of insect resistance. Mass trapping using traps baited with the female-produced sex pheromone is an attractive alternative for the management of this pest. The current study evaluated several commercial trap designs for capture of T. absoluta. Based on its small size and ease of handling, the most effective trap is a small plastic container with entry windows cut on the sides filled with motor oil over water. These traps are most effective when placed near ground level. Tests of septa containing 0.1 or 0.2 mg of the pheromone (95:5) E4, Z8-14Ac/E4,Z8,Z11-14Ac were slightly more attractive than septa loaded with 0.5, 1.0, or 2 mg during the first week of use, but the latter three loadings were slightly more attractive than the first two loadings after 9 weeks. Ideal trap baits were loaded with 0.5 mg of pheromone. Higher numbers of T. absoluta were captured near upwind borders of tomato fields suggesting that treatments against T. absoluta should be concentrated near upwind parts of fields. Comparisons of conventional insecticide treatment versus mass trapping to manage T. absoluta damage in three different test sites showed that even when initial captures in monitoring traps were high (>35 males trap^?1 day^?1), mass trapping at 48 traps/ha reduced leaf damage more efficiently than conventional insecticide treatment. Based on the typical insecticide recommendations against T. absoluta, mass trapping is an economically viable alternative.     

The use of barrier-connected pitfall trapping for sampling predatory beetles and spiders

The efficiency of barrier-connected pitfall trapping was compared to conventional single traps or arrays. For ground-active beetles, the use of a pitfall system incorporating a wetting agent with five traps arranged in a cross formation connected by plastic barriers was more efficient than a single dry trap by at least an order of magnitude and at least twice as efficient as five traps without connecting barriers. It is argued that the efficiency of pitfall trapping may be improved markedly by using barrier-connected traps, particularly for some carabid and staphylinid beetles and lycosid spiders. Capture of linyphiids was not improved by the use of barriers and was dependent only on the use of wetting agent and number of traps used.     

Studies on the effects of bait and sampling intensity on trapping and estimating Wood mice, Apodemus sylvaticus

The effects of baiting a Longworth trap with whole oats and the density of traps on an area, or sampling intensity, on trapping and estimating Wood mice were studied on two neighbouring woodland plots in November 1971. Standard capture-mark-recapture (CMR) methods were used for two weeks followed by five nights of removal trapping.
The presence of bait significantly increased the likelihood of capturing marked and unmarked animals. By increasing the sampling intensity a greater proportion of the population was sampled, although the number of animals captured per trap night decreased. These results have been related to the "effective" number of traps on an area.
Observations on population structure, weather, movement and capturing marked and unmarked animals have been made. CMR population estimates closely resembled the cumulative number of individuals captured in each study and were for the main part lower than the estimates from the removal trapping carried out at the end of the studies.     

Physical Factors Influencing Orientation of <Emphasis Type="Italic">Tyrophagus putrescentiae</Emphasis> (Schrank) (Sarcoptiformes: Acaridae) to Food-Baited Traps

Tyrophagus putrescentiae (Schrank) (Sarcoptiformes: Acaridae) is a serious pest of post-harvest durable stored food products for which traps are being developed as important tools for integrated pest management. This work addresses the effects of trap design, trap location, time of response, and light on the orientation of released groups of 7200 pedestrian T. putrescentiae to food-baited traps in experimental rooms maintained in full darkness at 28 °C and 70% RH. A standard trap made from a disposable Petri dish and four commercially produced stored-product pest traps of different designs were compared and evaluated for efficacy in trapping mites. Subsequent experiments evaluated the effect of trap placement, trapping duration, and light on mite capture. More mites were captured in the standard Petri dish trap when compared singly or side by side with four different commercial trap designs, so the standard trap was used in all other studies. Further experiments found that mites could be trapped 1 h after release at a distance of 2 m from the release point and at six meters from a mite source within 24 h. A greater number of mites were caught in traps placed along a wall than those away from a wall, demonstrating thigmotaxis to an edge. Traps at various heights on a shelf rack suggested that walking mites tended to be positively geotactic whether the source of mites was from the floor or from the top shelf at 1.8 m from the floor. More mites were caught in black-painted traps than in unpainted clear plastic traps in fully lighted rooms, suggesting that mites seek refuge from brightly lighted conditions. Light emitting diodes deployed with traps or assayed alone determined mites oriented positively to traps with violet or ultraviolet, with least preference to green, yellow, red and white lights. This research provides new information on orientation by T. putrescentiae that may help optimize trap designs and trap deployment for pest management decisions.     

Effects of pitfall trap size and sampling duration on collection of ground beetles (Coleoptera: Carabidae) in temperate forests

Pitfall trapping is a standard sampling method to compare the abundance or community structure of ground beetles. However, effects of sampling duration on biodiversity estimation of ground beetles according to different trap sizes have not been experimentally evaluated in temperate forests in Korea. Therefore, the objective of this study was to determine the interaction between trap sizes (SB, small‐sized bottle; MB, medium‐sized bottle; PC, plastic cup; PJ, plastic jar; PT, perforated type trap; FT, funnel‐type trap) and sampling duration (T1, 2 weeks × 2 sessions, 28 days; T2, 2 weeks × 4 sessions, 56 days; T3, 4 weeks × 2 sessions, 56 days) on estimation of ground beetle assemblages in Naejangsan National Park, a temperate forest in Korea. Funnel type and larger pitfall traps collected higher numbers of individuals and species than other trap sizes. Species composition of ground beetles was different by size of traps (SB, MB, and PC vs. PJ, PT, and FT). In particular, ground beetle composition in larger traps (PJ, PT, and FT) appeared to be influenced by environmental characteristics according to localities (e.g., soil characters and dominant tree species). These findings from our study support that pitfall trapping of ground beetles can be influenced by trap sizes per se as well as sampling durations and environmental characteristics. Thus, biodiversity monitoring in temperate forests should be conducted with long sampling duration (at least 28 days) using large‐sized traps (> 7.5 cm in diameter of trap mouthpart) considering expenses and study aims.     

Pitfall trap design affects the capture efficiency of harvestmen (Opiliones) and millipedes (Diplopoda)

Pitfall trapping is one of the standard methods used for the capture of ground‐active arthropod groups. Despite being frequently used, the standardization of this method is problematic due to the large range of combinations of the individual parameters of pitfall traps with varying efficacy under different environmental conditions. We evaluated the effects of the trap diameter, the fixing fluid, and their combination on the capture efficacy for harvestmen (Opiliones) and millipedes (Diplopoda). We used pitfall traps with three different diameters: 3 cm, 5 cm, and 12 cm, filled with three types of fixing fluids (saturated fluid of NaCl, 10:1 mixture of 70% ethanol and glycerol and 4% formaldehyde). Altogether, 90 traps representing nine combinations of trap diameters and fixing fluid were placed on a mown meadow in spring and autumn intervals for a total of 45 days. We sampled 1,488 individuals representing 11 harvestmen species and 881 individuals representing 11 millipede species. Large (d = 12 cm) and medium (5 cm) traps captured significantly more millipede species and individuals than the small‐sized traps (3 cm). The same effect was observed for harvestmen species richness, whereas the medium traps (d = 5 cm) captured the highest mean activity of harvestmen. By analyzing the differences in the body sizes of the studied arthropods in relation to the trap diameter and fluid, we found that larger traps, as well as traps filled with NaCl solution, captured larger harvestmen more frequently than the other trap types. Our results revealed that the combination of larger traps (d = 5 and 12 cm) and formaldehyde was most effective in the capture of both studied groups. However, the disadvantage of formaldehyde is its toxicity.     

Trap style influences wild pig behavior and trapping success

Despite the efforts of many natural resource professionals, wild pig (Sus scrofa) populations are expanding in many areas of the world. Although many creative techniques for controlling pig populations are being explored, trapping has been and still is the most commonly used method of population control for many public and private land managers. We conducted an observational study to examine the efficiency of 2 frequently used trap styles: a small, portable box-style trap and a larger, semi-permanent, corral-style trap. We used game cameras to examine patterns of trap entry by wild pigs around each style of trap, and we conducted a trapping session to compare trapping success between trap styles. Adult female and juvenile wild pigs entered both styles of trap more readily than did adult males, and adult males seemed particularly averse to entering box traps. Less than 10% of adult male visits to box traps resulted in entries, easily the least percentage of any class at any style of trap. Adult females entered corral traps approximately 2.2 times more often per visit than box traps and re-entered corral traps >2 times more frequently. Juveniles entered and re-entered both box and corral traps at similar rates. Overall (all-class) entry-per-visit rates at corral traps (0.71) were nearly double that of box traps (0.37). Subsequent trapping data supported these preliminary entry data; the capture rate for corral traps was >4 times that of box traps. Our data suggest that corral traps are temporally and economically superior to box traps with respect to efficiency; that is, corral traps effectively trap more pigs per trap night at a lower cost per pig than do box traps. © 2011 The Wildlife Society.     

Efficient sampling of ground-dwelling arthropods using pitfall traps in arid steppes

Pitfall trapping is probably the most frequently used method for sampling ground-dwelling arthropods. While the capture of specimens in pitfall traps largely depends on the number of individuals in the sampled area, trap design and trapping effort for a given environment, can also affect sampling success. The aim of this study was to determine the best pitfall trapping design for collecting ground-dwelling arthropods in the wind-blown and cold arid steppe areas of Patagonia. We tested four designs of traps, six types of preservative and different times of activation as well as the quantity of traps. Both preservation attributes and sampling efficiency differed between different trap designs and fluids compared. We conclude that in order to obtain reliable data on the structure of a community of ground-dwelling arthropods in Patagonia, at least three pitfall traps per experimental unit are required. In addition, traps should be opened for a minimum of 10 days filled with 300 ml of 30% ethylene glycol. We also suggested the use of a simple trap design (i. e. without funnel or roof). We believe these findings will contribute to more appropriate sampling of the ground dwelling fauna of Patagonia as well as other arid areas, leading to more reliable diversity studies.     

Optimizing control programmes by integrating data from fine-scale space use by introduced predators

The control of introduced mammalian predators (IMP) through trapping campaigns relies on operator experience to deploy traps in sites with an expected high probability of IMP presence, where the maximum number of captures is anticipated. We tested the limitations of available information on fine-scale spatial use by feral cats modelled from remote data collection methods (small-resolution satellite imagery and GPS-telemetry) in an intensive control campaign conducted over 8 years in an ecologically sensitive area of New Zealand. We calculated dichotomous optimal/sub-optimal areas for cats and found that operators placed traps in or close to optimal areas. Over a continuous range of probabilities of cat use, trap sites were not principally placed in hot spots of cat use. Logistic regression revealed that the probability of cat use was significantly associated with the probability of capture. However, regressing catch-effort against the probability of cat use showed no association between sites of high probability of cat use and higher capture rates. The incorporation in the models of bait, trap type, and habitat suitability for rabbits, as variables of operator’s choice showed that rabbit suitability, and the combination of baits/traps were significant. Results suggest that trapping feral cats is a complex process that likely relies on variables of space, time, and individual cognition. However, control programmes could improve trap deployment by identifying sites of high probability of cat use to maximize capture probability, while traps in sub-optimal areas could be removed (cost reduction), reallocated to optimal areas, or used to “fence” core conservation areas.     

Visual Responses of Adult Asian Citrus Psyllid (Hemiptera: Liviidae) to Colored Sticky Traps on Citrus Trees

The effects of five differently-colored sticky traps in capturing adult Diaphorina citri were evaluated in citrus orchards. Trap catches of D. citri were monitored fortnightly on blue, green, red, white and yellow sticky cards placed on three citrus varieties during D. citri active flight period from April to July in south Texas. Evaluation of mean trap catches of each color by repeated measures analysis of variance produced three separate groups: yellow traps caught significantly more D. citri adults than the other four traps; red and green traps caught significantly more D. citri than blue and white traps, which were not significantly different. Although the number of adult psyllid captured on all trap types significantly increased with time during the trapping period, the performance of traps did not change with time. Trap catches were also significantly influenced by the citrus species; traps placed on lemon trees captured more D. citri than those placed on sweet orange and grapefruit, suggesting that plant preference exhibited by D. citri may influence the performance of traps. The ratio of trap reflectance between the 680 to 700 nm and the 450 nm was significantly correlated with total trap catches in all host species studied. Thus, this index was a good indicator of the attractiveness of adult D. citri to colored traps. Additionally, we compared the reflectance values of young versus mature flush shoots of the three host plants used in this study as related to densities of D. citri recorded in colored traps. We discussed the importance of visual cues in the host finding behavior of adult D. citri.     

The effect of odour on trap response in Microtus townsendii

To investigate trap response of Microtus townsendii we set dirty Longworth traps soiled with faeces, urine and other debris and clean Longworth traps washed in hot water in field plots. Voles entered dirty traps significantly more than clean traps. This result was more pronounced in new animals and in young animals. When all clean or all dirty traps were set on a field plot, a much larger proportion of the animals known to occur on an area were caught in dirty traps than were caught in clean traps. This effect was most pronounced in the summer and fall period and was strongly correlated with the presence of breeding females.