The central component of mosquito and vector surveillance programs globally is the adult mosquito trap, which is intended to collect host-seeking mosquitoes. The miniature CDC trap is a widely distributed trap style in part due to its relative affordability and compact nature. Despite already being a simple trap, in-house production methods, such as 3D printing, could improve the accessibility of the CDC trap by eliminating some of the supply chain variables. We present here several trials with the Salt Lake City (SLC) trap, a three-dimensional (3D) printed trap design. Functional assessments were made on secondary components and found no statistically significant differences when comparing CO₂ line height (above vs. below fan), battery types (sealed lead acid vs. USB battery pack), and trap body collection shape (funnel body vs. simple/straight body). The SLC trap was compared directly to a commercial equivalent, the ABC trap, with comparative assessment on species diversity and evenness in collections and found to be statistically equivalent on all metrics. Methods also detail an accompanying optional transport system for a pressurized CO₂/regulator set-up, should a practitioner elect not to use dry ice. Our final design is presented here with the publicly published stereolithography (STL) files and a detailed outline of the transport container system. Alternative models are available for in-house manufacture of mosquito traps, and we contribute these designs in an effort to stimulate further growth in vector surveillance.

A prototype trap design, referred to as the SLC trap, was developed from a variety of exploratory model tests that are found in supplemental figures (Suppl. Fig. 1). Essentially, the prototype is a 1-piece tubular trap body with a rain guard (Fig. 1A). A 6-volt variable speed motor (RF-500TB-14415-R-J/32, Nichibo Taiwan Corp., Taipei, Taiwan) was equipped with a 4-blade, 7.5-cm propeller (Item #3C078RSHC1, Thorgren Tool & Molding, Inc., Valparaiso, IN) and secured inside the trap body with #2 conduit hanger (#2 ACC Conduit Hanger, Halex/Scott Fetzer Co, Cleveland, OH). All trap models can be operated using 18-guage, Class 2 copper wire (16-strand dual conductor/182C-200SR, MaxBrite LED Lighting Tech LLC, San Jose, CA). All 3D-printed components were fabricated from PLA plastic filament extruded through a 0.6 mm nozzle with set temperature at 210 °C (410 °F) and 58 °C (136 °F) bed temperature. The comparison model was the Clarke (or Pacific Biologics, AUS) branded ABC trap, with the light removed (Clarke Mosquito Control, St. Charles, IL), which is primarily composed of polyethylene and PVC plastics to make a trap body and rain guard (Fig. 1B).

Trap Evaluation Scheme

Field sites were selected from historical surveillance locations of the Salt Lake City Mosquito Abatement District (SLCMAD) in environments containing a mixture of wetlands and sagebrush. Site 1 was closest to the Great Salt Lake and was composed of muddy shores and salt playas (Fig. 2). Site 1 was furthest removed from human influence and in the heart of shorebird and waterfowl habitats in wildlife sanctuary lands. Site 2 (Fig. 2) was in the fringes of alkaline mudflats encroached by the Great Salt Lake and composed of a mix of palustrine flood plains and salt desert shrublands that were adjacent to animal agricultural lands. Site 3 was the furthest north location (Fig. 2) and was in the freshwater overflow for nearby reservoirs. Site 3 was characterized by saline meadow seeps and saline wetlands and was well outside any human occupied areas. The majority of mosquitoes historically occupying these environments was split between Aedes dorsalis (Meigen) and Culex tarsalis Coquillett. For SLCMAD, Cx. tarsalis is a priority vector of West Nile virus. Lights have been previously shown to confound vector Culex sp. collections the same general eco-region, in addition to increasing non-target insect numbers (15). Therefore, all trap nights, regardless of model, excluded the use of a light source.

Surveillance was conducted with 1 kg dry ice according to Sriwichai et al. (5) for trials comparing the SLC trap to the commercial model ABC trap. For experiments that were done for comparing various trap modifications to the SLC trap, the CO₂ source was from a regulated compressed cylinder at the rate of 250 ml/min.  For all trials traps were set for 24 hrs and trap collections were counted and identified with a hybrid camera and microscopy set-up using ImageJ (16). Species identifications were keyed according to Darsie and Ward (17). Tests were conducted with different supplies and components to optimize the base model SLC trap. Pairwise comparisons were conducted for SLC trap modifications were conducted exclusively at site 1. Tests were conducted between: CO₂ dispensed high or low on the trap body (8 replicates); 6-volt sealed lead-acid batteries (PS-6100 6v 12Ah, Power Sonic Co., San Diego, CA) and USB battery packs (PowerCore 20 100mAh, Anker Innovations Co., Ltd, Hunan, China) (10 replicates); a funneled housing option (Suppl. Fig. 2) (4 replicates). For comparison of the SLC trap to the commercial model ABC trap (positive control), tests were replicated 4 times each at sites 2 and 3 for a total of 8 comparison nights. Whether doing accessory tests or the positive control comparison, both traps were present at the same site but spaced at least 100 m apart. Additional minor tinkering was conducted for transport container types, comparing tool boxes, buckets, and metal ammo cans. These transport containers were investigated for optional use with a pressure regulated CO2 cylinder system (moot in the case of dry ice, which can be carried in a separate cooler).

Transport containers were selected based on size, ruggedness and long-term service potential (Suppl. Fig. 2, Suppl. Fig. 3). Although it is suitable to embed the battery and CO₂ source in a toolbox or bucket (Suppl. Fig. 2), the desire for space efficiency and durability led to selection of a re-purposed metal ammunition can from military surplus (Fig. 3, Fig. 4) for operational use at SLCMAD. The resulting final surveillance trap and container design was specially built around using a pressure-regulated CO₂ cylinder system.

SLCMAD chose to adopt a pressure-regulated CO₂ cylinder system after the above trials were conducted on trap design. Cylinder regulators were modified with a complex series of small parts to feed the gas safely to a lower CO₂ line attachment (Fig. 3). A “¼ in to #10-32 reducer” (4CQF-ENP-PKG, Clippard Instrument Laboratory, Inc., Cincinnati, OH) was reinforced with PTFE tape and attached directly to the lower regulator. Short coupling O-rings (11999-PKG, Clippard Instrument Laboratory, Inc., Cincinnati, OH) were seated on both sets of threads of a “#10-32 connector” (11999-PKG, Clippard Instrument Laboratory, Inc., Cincinnati, OH), which was then screwed into the reducer. The reducer starts with a “0.0075 in diameter air choke” (CD-C, Clippard Instrument Laboratory, Inc., Cincinnati, OH) that is fitted with a choke disk inside the curved (non-faceted) end of the piece, then screwed onto the remaining threads of another “¼ in to #10-32 reducer”. The faceted end of the air choke is finished by screwing in a “#10-32 to ¼ in ID hose fitting” (11752-1-PKG, Clippard Instrument Laboratory, Inc., Cincinnati, OH) (Fig. 3). The CO₂ line extends off the lower choke assembly (Fig. 3) and attaches to the underside of a PA70 ammo can measuring 42 cm × 30.5 cm” × 15.9 cm (B643, 8-Cartridge, 60MM, HE, M888 for M224 Mortar, United States Military Surplus) with another brass “#10-32 to ¼ in ID hose fitting.”

For the transport container itself, the top side of the ammo can lid was fitted with a female push-to-connect piece (Airbrush Quick Release Coupling ⅛-in BSP, Point Zero Ltd., China) that receives the male end (Fig. 4) when traps are deployed. To brace the CO₂ cylinder inside the ammo can, 7-8 cm wide thermoforming plastic sheet (Sekisui Kydex, Bloomsburg, PA) was softened with a heat gun and then molded around the cylinder (Suppl. Fig. 3). After cooling to form, the sheet was riveted inside the ammo can to create a holster for the cylinder (Suppl. Fig. 3). The opposite end of the ammo can interior was then reinforced with padding, in this case with duct tape strips, so as to pad the batteries and prevent contact with the battery terminals. (Suppl. Fig. 3). Once complete, the transport containers receive a 6v battery, filled CO₂ cylinder, and associated trap with collection net (Fig. 4).