Ethics statement

The North Carolina State University Institutional Review Board (IRB) approved this study (#1459). Before participation, adult participants (> 21 yrs. old) provided written informed consent. Demographic data on participants were not gathered in this study, as we were interested in a cockroach intervention and the environmental outcomes in cockroach-infested residences, independent of the demography of the residents.

Recruitment of participants

Apartments in five low-income communities within the city of Raleigh NC, U.S.A., were visited and residents were queried regarding cockroach infestations. Apartments were in multi-unit low-rise buildings, duplexes, and row homes. Residents were first informed of the purpose of the study, provided informed consent, then asked if (a) they had seen any live cockroaches, and (b) if they were interested in participating in the study. If the resident reported seeing cockroaches and agreed to participate, the home was visually inspected for the presence of cockroaches. If the home was expected to qualify based on sufficient numbers of live German cockroaches or evidence of cockroaches, the home was recruited into the study. Official enrollment followed standard cockroach population quantification, implemented through trapping (see “Intervention effectiveness – Assessment of relative cockroach population size” below).

Interventions

Four different TRF products were used, representing several insecticide active ingredients and manufacturers: Hot Shot No-Mess Fogger 2 with Odor Neutralizer (Hot Shot 2; 85 g, 0.333% tetramethrin, 0.834% permethrin, 1.667% piperonyl butoxide; Spectrum Group-United Industries, St. Louis, MO, U.S.A.), Hot Shot No-Mess Fogger 3 with Odor Neutralizer (Hot Shot 3; 170 g, 0.200% tetramethrin, 0.860% cypermethrin, 0.500% piperonyl butoxide; Spectrum Group-United Industries), Raid Max Concentrated Deep Reach Fogger (Raid Deep; 60 g, 1.716% cypermethrin; SC Johnson, Racine, WI, U.S.A.), and Raid Fumigator (10 g, 12.600% permethrin; SC Johnson). Five replicate homes were treated with each TRF product, one home in each of five apartment complexes (20 TRF-treated homes).

Each TRF was discharged in the kitchen following the product label instructions and EPA precautions (https://www.epa.gov/safepestcontrol/safety-precautions-total-release-foggers; last accessed April 15, 2017). Briefly, all residents vacated the apartments for 4–6 h, windows and doors were closed, air conditioning and gas stove pilot lights were turned off, cabinet doors were opened and contents as well as immovable kitchen appliances were covered with newspapers, and aquaria were moved out of the kitchen. Four to six hours later, the apartment was ventilated, newspapers discarded, dishes rinsed, and residents allowed to re-enter.

Running in parallel, 10 additional apartments were treated with only gel baits. Five homes, one in each apartment complex, were treated with a consumer bait, Combat Gel Bait (0.010% fipronil; Combat Insect Control Systems-The Dial Corporation, Scottsdale, AZ, U.S.A.), and another set of five homes, one in each apartment complex, received a professional bait, Maxforce Gel Bait (0.010% fipronil; Bayer Environmental Science, Robinson Township, PA, U.S.A.). Bait was dispensed as needed at each of three visits (baseline, two weeks, one month). At the conclusion of the study, all TRF-treated apartments were provided thorough gel bait interventions.

Intervention effectiveness – Assessment of relative cockroach population size

At baseline, and subsequently two and four weeks after treatment, six glue-board sticky-traps (Victor Roach Pheromone Trap, Woodstream Corporation, Lititz, PA, U.S.A.) were placed in kitchen locations where cockroaches commonly aggregate. The traps were collected the following day and enumerated in the lab. Changes in each cockroach population (apartment) were assessed relative to the baseline trap catch. Homes were enrolled in the study if at least 50 cockroaches were trapped at baseline.

TRF efficacy – Caged sentinel cockroaches

After enrollment, cockroaches were collected from the kitchen using a modified Eureka Mighty-Mite 7.0-A vacuum cleaner (Eureka Company, Charlotte, NC, U.S.A.). Live cockroaches were collected into a mesh-lined plastic tube attached to the distal end of the vacuum’s extension tube. Apartment-collected male cockroaches were used as caged sentinels for determining product efficacy in the same apartment where they were collected. Prior to discharging the TRF, 40 laboratory raised, insecticide-susceptible adult male cockroaches and 40 home-specific apartment-collected males were placed into the home as sentinels. Twenty cockroaches from both the laboratory population and the apartment-specific population were placed in two uncovered cages on the floor 1.0 m away from the TRF (referred to as “floor”), and the other 20 cockroaches from each population were placed in two uncovered cages in an upper cabinet (lowest shelf, referred to as “upper cabinet”). The inside walls of the cages were coated with petroleum jelly to prevent cockroaches from escaping. Four to six hours after the TRF was discharged, and it was safe to re-enter the apartment, the sentinel cockroaches were collected, returned to the laboratory, transferred to a clean cage, and assessed for mortality 24 h later.

Pesticide residue analysis

Kitchens were sampled for insecticide residues at three time points during the study: before TRF use (baseline), immediately (4–6 h) after TRF discharge, and one month later. Areas sampled included the floor at both 0.5 m and 1.0 m from the site of the TRF, the nearest countertop to the TRF (~ 0.9 m high), the inside (base) of an upper level cabinet (~ 1.4 m), and the nearest wall to the TRF at a height of 0.9 m (representing the height of a child). The same areas of the kitchen, but not the same spots, were sampled at each subsequent visit. Samples were collected by wiping an area of 100 cm2 with a cotton swab wetted with isopropyl alcohol for 1 min. Each swab sample was placed into a 20 ml glass vial, immediately returned to the laboratory and stored at − 30 °C until extraction.

Swab samples were analyzed for the specific active ingredients used in the TRF products, which included permethrin (sum of cis- and trans- isomers), cypermethrin (sum of all isomers), tetramethrin (sum of all isomers), and PBO (pyrethroid synergist). Additionally, swab samples were analyzed for fipronil residues (active ingredient from baits used). Each sample was fortified with 500 ng of the surrogate recovery standard (SRS) 13C 6 -trans-permethrin (Cambridge Isotope Laboratories Inc., Tewksbury, MA, U.S.A.). Samples were extracted and sonicated twice with ethyl acetate. Solvent volume was then reduced, and samples were cleaned using a 3 ml prefabricated solid phase extraction (SPE) column containing 500 mg of silica gel (Supelclean LC-Si SPE Tube, Sigma Aldrich, St. Louis, MO, U.S.A.). The SPE column was conditioned with 5 ml of hexane, the sample was loaded onto the column and eluted with 5 ml of 50% ether in hexane. Each eluted sample was spiked with 500 ng of the internal standard (IS) 4,4′-dibromobiphenyl (DBBP, AccuStandard Inc., New Haven, CT, U.S.A.), evaporated to near dryness under nitrogen, resuspended in 1 ml of hexane, and stored at − 30 °C until analysis.

Samples were analyzed using an Agilent Technologies 6890 GC coupled to an Agilent 5975 mass spectrometer (GC-MS). The GC was equipped with a 30 m × 0.25 mm × 0.25 μm (5%-phenyl)-methylpolysiloxane Agilent J&W HP-5 ms column preceded by a 3 m deactivated guard column. The temperature program was: 100 °C for 1 min, then 5 °C/min to 225 °C, then 2 °C/min to 256 °C, then 10 °C/min to 320 °C where it was held for 10 min. Mass spectrometry conditions were: transfer line at 280 °C, ionization source at 230 °C, and quadrupole at 150 °C. One quantification ion was used for each pesticide (Table 1). Ten calibration curve solutions ranging from 0.1 μg/ml to 100 μg/ml for all TRF insecticides (Sigma-Aldrich) were used to generate calibration curves via log-transformed linear regression. Extracted samples were corrected for both the SRS and IS and quantified using the calibration curve. Each calibration curve solution was run a minimum of three times, interspersed evenly among field-collected samples. If any compound exceeded the upper point in the calibration curve by more than 15%, the sample was diluted and re-analyzed. Method detection limits (MDLs) were determined using the guidelines from 40 CFR Part 136, Appendix B.

Table 1 Retention times, quantification ions, and qualification ions for insecticide residue analyses by GC-MS. Full size table

Data analyses

Two-way repeated measures ANOVA was used to compare changes in cockroach population levels over time (baseline, two weeks, four weeks) among different treatments (TRFs and baits). Due to interactive effects, repeated measures ANOVA was used to evaluate changes in cockroach population within each treatment, with means at different times compared using the Tukey-Kramer multiple comparison test.

Three-way ANOVA was used to compare sentinel cockroach percent mortality (arcsine square root transformed) among TRF products, population (laboratory-raised or apartment-collected), and location (floor or upper cabinet).

The effects of each TRF treatment on insecticide residues were evaluated using repeated measures ANOVA (within each treatment) on log-transformed values. Treatments were defined by the insecticide(s) in each TRF product and swab locations quantified over time, with means at 4–6 h and one month after the TRF intervention compared to the baseline mean using Dunnett’s test. Prior to log-transformation, all values had the respective insecticide MDL added to them. Comparisons were also made among swab locations for each TRF treatment 4–6 h after discharge using ANOVA. Insecticide residues were evaluated only for the Combat gel bait group, and not the Maxforce bait group, at baseline and one month. Additionally, three apartments were removed from the study for either failing to complete the study or not following the approved protocol. Also, some samples have missing values due to problems with sample collection or sample analysis (reflected by sample size).

All statistical analyses were performed using SAS 9.4 (SAS Institute, Cary, NC, U.S.A.).