Field Comparison of Carbon Dioxide Source with Biogents Sentinel-2 and Pro Traps for Adult Aedes Mosquito Surveillance

The choice of field sampling method for female mosquitoes is focused on the host-seeking behavior of the target species, and this is especially true regarding disease vector surveillance. Aedes aegypti and Aedes albopictus are primary targets of many mosquito control and surveillance programs given their role as vectors for arboviruses such as chikungunya, dengue, yellow fever, and Zika (Kraemer et al., 2015). With the global distribution of these Aedes vectors the need for effective trapping methods to detect these species is crucial.

New traps and baits have developed in recent years to target the capture of Aedes mosquitoes. The BG Sentinel-1 (BGS-1) was introduced in 2004 (Biogents AG, Regensburg, Germany) and was widely adopted by the mosquito research community as the new standard to collect this vector (CDC 2018). Biogents later improved the durability of this trap and introduced the BG Sentinel-2 (BGS-2) in 2014. Most recently, Biogents developed a “3-in-one” modular trap (BG-Pro) that incorporated the design features of a CDC, Encephalitis Vector Surveillance (EVS), and BG Sentinel trap, the latter specifically to survey for Aedes mosquitoes. At the same time, Biogents also introduced a novel yeast-derived CO₂ generator as an alternative to conventional dry ice or pressurized CO₂ for use in their BG-Pro. We report here on the comparative effectiveness of the standard BGS-2 with the BG-Pro trap baited separately with either dry ice, pressurized CO₂ gas, or BG CO₂ generator as attractants to capture Aedes vectors and other mosquito species for surveillance purposes.

Evaluations were conducted in the city of Gainesville, FL at 4 locations: a cemetery (29.625970, –81.824110) and three residential properties (29.656070, –82.331630; 29.6568391, –82.3357427; 29.69920, –82.38085) from July through August 2022. All locations had a previous documented history of Ae. albopictus and Ae. aegypti populations (Y Jiang, pers comm). The cemetery and one of the residential properties were large enough for placement of two traps at least 100 m apart in each location and positioned so that they were not visible to one another, the remaining 2 properties consisted of 1 trap each (n=6 total sample locations). Each of the 4 properties were at least 5 km from one another.

BGS-2 and BG-Pro (the latter as a BGS-2 configuration, i.e., positioned on ground surface) were baited separately with either dry ice, pressurized CO₂, or the BG-CO₂ generator. In addition, a BG Sweetscent cartridge lure was inserted into each trap as suggested by the manufacturer. Carbon dioxide produced by dry ice consisted of 1.5 kg dry ice pellets in a 2.0 L Igloo container suspended above each trap with a tube inserted from the bottom of the container into the air intake of the trap. Pressurized carbon dioxide was delivered at 200 ml/min via a manufacturer preset regulator (Bioquip, Inc. El Rancho, CA). Yeast-derived CO₂ was delivered via a BG-CO₂ generator (75–125 ml/min) using Biogents proprietary yeast product per manufacturer’s instructions (Biogents AG, Regensburg, Germany). The generator yeast product was replaced daily. Because the BGS-2 does not possess lights, the light string was removed from the BG-Pro sentinel set up. In addition, all traps were protected from rain with a 52-cm diameter translucent plastic lid affixed 29 cm above each trap (Degener et al. 2021).

The study followed a 6x6 Latin square design. Three rotational repetitions were performed among the six trap locations with initial random assignment of a specific trap and location at the start of each full 6-day rotation. Trap contents were collected daily at 24 h intervals. Female mosquitoes were identified to the species level using the taxonomic key of Darsie and Morris (2003) and used in the reported data. Overall mosquito abundance data were log x+1 transformed prior to analyses. Initially, data were subjected to an ANOVA with a Tukey pair-wise mean comparison test (R Core Team 2023) was performed on the overall mosquito abundance data for each trap and CO₂ source, as well as Ae. aegypti and Ae. albopictus to determine differences (P≤0.05).

During the 8 wk study, 5,256 mosquitoes were collected; BGS-2 collected 3,952 and BG-Pro collected 1,294. Even though there was a difference in overall abundance for each trap type, both generally collected a relatively similar percentage of each species to total collection (Table 1). Sixteen species were collected from the BG-Pro and 15 in the BGS-2. Culiseta melanura (Coquillett) was absent from the BGS-2, presumably due to relatively low seasonal population and relative location in northern Florida at the time of sampling (Burkett-Cadena et al. 2015). The top three most abundant species collected from both traps were Mansonia titillans (Walker) (55.9%), Ae. albopictus (14.5%), and Ae aegypti (6.2%).

Overall, we found a significant difference in the number of mosquitoes collected between the BGS-2 and BG-Pro (F = 23.24, df = 1, 2, P < .001) (Table 2). The BGS-2 paired with dry ice or pressurized CO₂ collected the most mosquitoes on average (Table 2). The BGS-2 may have performed better as a result of the black outer surface of the BGS-2 trap being more attractive than the white outer covering of the BG-Pro. Bidlingmayer and Hem (1979) and Alonso San Alberto et al. (2022) have shown such preferences exist regarding visual contrast of mosquitoes to light and dark objects.

In our investigation we found that CO₂ source did significantly impact the number of mosquitoes collected (F = 8.87, d = 1,2, P <0.001). Out of our CO₂ sources, dry ice baited traps collected more mosquitoes on average (Table 2). The BGS-2 baited with dry ice collected the most mosquitoes compared to all trap and CO₂ configurations (Table 2). The BG-Pro traps baited with pressurized CO₂ and the yeast generator performed similar to the BGS-2 with yeast (Table 2). The BG-Pro traps baited with the pressurized CO₂ collected the fewest mosquitoes (Table 2). Regardless of trap, dry ice outperformed pressurized CO₂ possibly related to an initially greater, but unregulated, release rate of CO₂ from the dry ice pellets.

When specifically examining Aedes collections we found that all trap and CO₂ configurations successfully captured Ae. aegypti and Ae. albopictus. We did see significant differences in the number of Ae. albopictus collected between trap type and CO₂ combinations (F = 5.3, df = 1,2, P = 0.006) but not for Ae. aegypti (F = 0.3, df =1,2, P = 0.7). It is plausible that the low numbers of Ae. aegypti captured may reflect the general low historical occurrence of this species within the city of Gainesville during the sample period. Previous studies in other countries by Degener et al. (2021) found that BG-Pro traps placed in locations with high Ae. aegypti density can significantly outperform BGS-2 but at lower density both traps yield similar results for this vector.

From an operational deployment standpoint, it is well known that supplemental carbon dioxide increases mosquito catch in mosquito traps (Carestia and Horner 1968). However, the availability of CO₂ sources may vary by locality and may not always be accessible. We found that yeast-derived carbon dioxide from the BG-CO₂ generator may be a viable alternative for use in either trap as it captured similar mosquito species and did not deter or prevent the collection of Aedes vector species. Further studies are required to fully understand how trap and CO₂ configurations can impact the collections of Aedes mosquitoes. These insights could provide valuable information needed to target specific vectors for disease surveillance.

The authors thank the City of Gainesville Mosquito Control District staff: Cason Bartz, Ivy Grob, and Sara Brennan for their technical assistance during this study.

The views expressed in this article are those of the authors and do not reflect the official policy or position of the Navy and Marine Corps Force Health Protection Command, Navy Bureau of Medicine and Surgery, Department of Defense, the US Government, or Gainesville Mosquito Control. This is a research report only. The name of the commercial products mentioned in this publication does not constitute nor imply endorsement by Gainesville Mosquito Control or the US Government. The authors include employees of the US Government. This work was prepared as part of their official duties. Title 17, U.S.C., §105 provides that copyright protection under this title is not available for any work of the US Government. Title 17, U.S.C., §101 defines a US Government work as a work prepared by a military Service member or employee of the US Government as part of that person’s official duties.