Lure Increases Efficacy of Pitfall-Style Traps

The business of bed bug control continues to grow in the United States. In 2016, revenue from professional bed bug control services and products in the U.S. reached $611.2 million (Anonymous 2017). A 2015 survey of the pest management industry shows 64 percent of companies felt bed bug incidences were increasing and 68 percent of companies regarded bed bugs as the most difficult to control among termites, ants, cockroaches and bed bugs (Potter et al. 2015).

A major challenge in bed bug management is the difficulty in detecting them when their numbers are small. Proper monitoring is vital for early detection as well as to confirm elimination after treatment. It is known that client reports and visual inspection can be unreliable for detecting bed bugs (Cooper et al. 2015, Wang et al. 2016). Placement of pitfall-style traps under the legs of beds and sofas, in combination with a client interview, proved to be cost-effective for the detection of bed bugs in large-scale, community-wide inspection programs (Wang et al. 2016, Vail and Chandler 2017). Pitfall-style traps take advantage of bed bug behavior and morphological characteristics: they tend to climb up a vertical surface and are unable to grip the smooth hard surface inside the trap.

Bed bugs are attracted to their hosts through host cues, which include carbon dioxide (CO2), body heat and chemicals released from the host (Wang et al. 2009). Among those host cues, CO2 is the most important attractant, but it is expensive or inconvenient to use for commercial applications (Anderson et al. 2009, Wang et al. 2009).

Recently, bed bug lures have been investigated for their potential use in monitoring programs (Siljander et al. 2007, 2008; Singh et al. 2012, 1015; Gries et al. 2015). To date, only one commercial formula (SenSci Activ Bed Bug Lure, Bed Bug Central, Lawrenceville, N.J.) is available and proven to be effective. In a field experiment it increased the trap catch by 7.2 times compared to traps without the lure when a CO2 source was present (Singh et al. 2015). Past evaluation of lure effectiveness used ClimbUp Interceptors (15 cm diameter, 2.2 cm deep) or inverted dog bowls (18 cm diameter, 6.4 cm deep). Although the SenSci lure is known to be effective, what is unknown is whether trap size and the lure release method affect the efficacy of the lure. Questions also exist regarding how long the lure remains effective. This study will answer these questions.

MATERIALS AND METHODS. The following insects, products and materials were used in these experiments.

Bed Bugs. Most experiments used bed bugs (Cimex lectularius L.) collected from multiple apartments in Indianapolis, Ind., in 2008. The last experiment used bed bugs collected from apartments in Irvington, N.J., in 2013. They were maintained in the laboratory in plastic containers with folded paper as harborages at 26^°C ± 1°C, 40 ± 10 percent relative humidity, a 12:12 hour (light:dark) photoperiod. Bed bugs were fed weekly on defibrinated rabbit blood (Hemostat Laboratories, Dixon, Calif.) using a Hemotek membrane-feeding system (DiscoveryWorkshops, Accrington, UK). Bed bugs were starved 9-18 days prior to bioassays.

Pitfall Traps. Different sizes of ClimbUp Insect interceptors (Susan McKnight Inc., Memphis, Tenn.) designed for monitoring bed bugs were used to evaluate the attractiveness of lures (Figure 1). All of them had a black paper tape on the exterior walls, because it has been shown the dark colors are more attractive to bed bugs compared to lighter colors. The sizes of these traps (interceptors) were 10, 15 and 23.5 cm in diameter, respectively; their height is 2.2 cm or 5.1 cm. A layer of fluoropolymer resin was applied to the inner walls of the traps in a similar fashion to confine the bed bugs that fell into the traps. We did not use talcum powder in the traps for preventing escape, as this can kill the bed bugs and we wanted to save the trapped bed bugs for other uses.

Experimental Arenas. Plastic tray arenas (80 cm by 75 cm by 5 cm: length by width by height) with the bottom lined with brown paper were used to evaluate the lure attractiveness (Figure 2). A layer of fluoropolymer resin was applied to the inner walls of the experimental arenas to prevent the bugs from escaping. A filter paper (15 cm diameter) was placed on the floor in the center of each arena, and then a plastic ring (13.3 cm diameter and 6.4 cm height) was placed on the filter paper for confining the bed bugs. Four paper harborages were placed in each arena to provide hiding sites for the bed bugs. Experiments were conducted in a 4 m long and 2.3 m wide walk-in chamber with an average temperature of 28.5^°C.

Bed Bug Lure. A mixture of nonanal, 1-octen-3-ol, L-lactic acid, and spearmint oil at 2:2:2:1 ratio by volume was prepared within one month before this study and stored in a sealed glass container at 40^°C. This formula is identical to that in patented SenSci Activ Bed Bug lure.

EXPERIMENT 1. The objective of this experiment was to find out the effect of trap size on lure performance. Two traps of the same size were placed in each arena (Figure 2). A 0.6 ml centrifuge tube containing cotton soaked with 20 ul of lure mixture was placed at the center of one of the traps. A total of 80 bed bug nymphs and male adults were placed at the center of each arena and confined with a plastic ring. Four arenas were set up simultaneously providing four replicates. The experiment started one hour into the dark scotophase by removing the plastic ring confining the bed bugs. Bed bug numbers in each trap were recorded after eight hours. Three different trap sizes (10, 15, and 23.5 cm diameter) were tested using the same method to evaluate the performance of the lure in different traps. The chamber was non-ventilated, completely dark, and without any CO₂ source during this experiment.

EXPERIMENT 2. The objective of this experiment was to determine the effect of lure release method on lure performance. Three lure release methods were tested: 20 ul lure in a centrifuge tube, 200 ul lure in a centrifuge tube, and 800 ul in a Sen-Sci Activ package, which is identical to the commercial SenSci Activ bed bug lure. We used 10 cm diameter ClimbUp interceptors in this experiment. Similar to Experiment 1, lure was placed in one of the traps within each arena. A total of 80 or 100 bed bug nymphs and male adults were placed at the center of each arena and confined with a plastic ring for one hour. Bed bug numbers in each trap were recorded after eight hours. Each lure release method was replicated four times. The chamber was non-ventilated, completely dark, and without any CO₂ source during experiment.

EXPERIMENT 3. The objective of this experiment was to gauge the effect of lure age on lure performance. We placed 800 ul lure in each blank SenSci Activ package with one corner of the package cut off to allow lure release following the exact same method as the commercial SenSci Activ lure. The opened lure was placed in the laboratory with average temperature of 25^°C and aged for a 1- to 3-month period. The experiment set up was same as Figure 2B. For comparing fresh lure and 1- or 2-month-old lure, a total of 80 bed bugs (20 nymphs and 60 male adults) were placed in each arena. The test chamber was completely dark, with no air current and no CO₂ source. For comparing fresh lure and 3-month-old lure, we placed a red light in the room (light intensity 0.92 lux), a small fan (13 cm diameter) that directed the air to the ceiling, and a CO₂ tank with CO₂ released at 200 ml/minute at center of the chamber to stimulate bed bug movement. The running fan helped mixing air with CO₂ and circulate the air. A few hundred mixed stages of bed bugs were placed in each arena. The use of more bugs per arena and the addition of CO₂ in the chamber in this test was due to the bed bugs not being very active in a preliminary test. In all tests, fresh lure and aged lure were tested in two arenas on the same day and repeated the next day to provide a total of four replicates. Bed bug numbers in each trap were recorded after 4-8 hours.

Analysis of variance (ANOVA) was used to compare the effect of trap size, release method and aging period on trap catches.

RESULTS AND DISCUSSION. What following are findings from the three experiments and future implications.

Experiment 1 (effect of trap size on lure performance). In all experiments, 17-44 bed bugs were captured in traps in each arena. Regardless of the size of traps, the baited traps always caught more bed bugs than the non-baited traps (Figure 3). The results confirm previous field experiment findings where an inverted dog bowl trap with lure caught 7.2 times more bed bugs than non-baited dog bowls (Singh et al. 2015). We found no significant differences in attractiveness of the lure among the three traps (F = 2.8, df = 2, 9; P = 0.11). Although we can see a trend that as the trap size increased, the difference in the trap catches between the lure baited and non-baited traps decreased.

Experiment 2 (effect of lure release rate on lure performance). In all experiments, 17-67 bed bugs were trapped in each arena. We found no significant differences in attractiveness of the lure among the three release methods (Figure 4) (F = 7.4, df = 2, 9; P = 0.50).

Experiment 3 (effect of lure age on lure performance). In all experiments, 17-41 bed bugs were trapped in each arena. We found no significant differences in attractiveness of the 1-month-old lure (F = 0.3, df = 1, 6; P = 0.60) and the 2-month-old lure (F = 0.1, df = 1, 6; P = 0.80) (Figure 5) when compared to fresh lure. Similarly, the 3-month-old lure performed similarly as the fresh lure (F = 0.6, df = 1, 6; P = 0.48) (Figure 6). Based on the lure weight measured at 0, 1, 2 and 3 month, the mean weight loss at 1, 2 and 3 month was 21, 28 and 35 percent, respectively. These results suggest the bed bug lure can remain effective for a minimum of three months once deployed. In the 2015 industry survey, companies took an estimated 2.6 service visits to control bed bug infestations (Potter et al. 2015). Field studies also show that a combination of brief visual inspection and placing pitfall style traps under furniture legs detected 89 percent of the bed bug infestations in apartments (Wang et al. 2016). Together, these data demonstrate placing lure-baited traps for 2-3 months and monitoring monthly would be an effective strategy for confirming treatment success.

CONCLUDING REMARKS. This study demonstrates that adding a chemical lure to various sized pitfall style bed bug monitors will increase the sensitivity of traps for detecting bed bugs. The lure formula tested can remain effective after deployment for at least three months. While the lure is helpful for increasing the trap effectiveness, there is potential for further improvement of the lure formula and release method. Based on current study, it seems the quantity and size of the SenSci Activ lure can be further reduced. It is also necessary to test the effectiveness of bed bug lure under field conditions and in various shaped traps.

Authors’ Acknowledgments

The authors thank BedBug Central for providing blank SenSci Activ packages. This study was sponsored by the Aresty Research Center of Rutgers University.

Conflict of Interest Statement

The senior author is the co-author of a patented bed bug lure that is licensed to two companies through Rutgers University.

Changlu Wang is an associate extension specialist at the Department of Entomology, Rutgers University, New Brunswick, N.J. Pei-Hsuan Chang is an undergraduate student at the School of Arts and Sciences, Rutgers University. Chen Zha is a doctoral student at the Department of Entomology, Rutgers University. Email changluw@rutgers.edu with comments about this article.

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