The study took place in Dutchess County, New York, which has experienced high incidence rates of Lyme disease and other tick-borne diseases since the 1990s (Eisen et al, 2016 (link)). We selected two tick control interventions that had been demonstrated in small-scale studies to be effective in reducing population size of blacklegged ticks and that were considered safe for people, pets, and the environment (Dolan et al, 2004 (link); Schulze et al, 2017 (link); Schulze et al, 2007 (link); Williams et al, 2018 (link)).
One intervention was the deployment of TCS bait boxes, which attract small mammals to a food source inside an enclosed device and apply the tick-killing chemical fipronil to these mammals. Fipronil is lethal to ticks but harmless to mammals (Dolan et al, 2004 (link)). The other intervention was the biopesticide Met52, which consists of spores of the F52 strain of the fungus Metarhizium brunneum. Met52 solution is mixed with water and sprayed on the ground and low-lying vegetation where ticks dwell. By killing ticks attached to small mammals, TCS bait boxes are expected to affect the abundance of host-seeking (questing) ticks the following year, whereas Met52 targets host-seeking ticks, with impacts expected within days to weeks after deployment.
As previously described in detail (Keesing et al, 2022 (link)), we selected 24 residential neighborhoods that had reported high incidence of tick-borne diseases in Dutchess County in recent prior years. Neighborhoods consisted of ∼100 adjacent 1- and 2-family residences at moderate to high density, including their respective yards. Overall average property size was 0.19 ha. After a year of exhaustive efforts to recruit eligible households in each neighborhood to participate in the study, we enrolled a mean of 34% of properties in each neighborhood (range 24–44%).
Each of the neighborhoods was randomly assigned to one of four treatment categories, with six neighborhoods assigned to each category: (1) active TCS bait boxes and active Met52; (2) active TCS bait boxes and placebo Met52; (3) placebo TCS bait boxes and active Met52; and (4) placebo TCS bait boxes and placebo Met52. All participating properties in each neighborhood received the same treatment category. Placebo TCS bait boxes were identical to active bait boxes except that they contained no fipronil. Placebo Met52 consisted of water only. Participating households agreed not to deploy broadcast acaricides independent of our study throughout its duration.
Both products were used according to label instructions. TCS bait boxes, covered with galvanized steel shrouds (active and placebo), were deployed twice annually, in spring and mid-summer, at an average rate of 5.9 boxes per property (38/ha), at least 10 meters apart, preferentially in sites frequented by small mammals. Active Met52 was sprayed by truck-mounted high-pressure sprayers (GNC Industries, Inc.) at a concentration of 2.22 L per 378.5 L of water. Placebo Met52 (water only) was sprayed using the same truck-mounted sprayers at the same rate of 4 L of spray per 93 m2 at a pressure of 1.2–1.4 MPa. Spraying of active and placebo Met52 occurred twice each year, immediately before (April—early May) and during (late May–late June) the peak activity period for nymphal blacklegged ticks in this region (Ostfeld et al, 2018 (link)). Further details are provided in the supplementary online appendix of Keesing et al (2022 (link)) (https://wwwnc.cdc.gov/eid/article/28/5/21-1146_article ).
The study design was double-masked ( = “double-blind”), in that neither the members of participating households nor the team of researchers collecting data were aware of the treatment category of any of the neighborhoods. All data collection, entry, and compilation were conducted with the treatment categories remaining masked.
One intervention was the deployment of TCS bait boxes, which attract small mammals to a food source inside an enclosed device and apply the tick-killing chemical fipronil to these mammals. Fipronil is lethal to ticks but harmless to mammals (Dolan et al, 2004 (link)). The other intervention was the biopesticide Met52, which consists of spores of the F52 strain of the fungus Metarhizium brunneum. Met52 solution is mixed with water and sprayed on the ground and low-lying vegetation where ticks dwell. By killing ticks attached to small mammals, TCS bait boxes are expected to affect the abundance of host-seeking (questing) ticks the following year, whereas Met52 targets host-seeking ticks, with impacts expected within days to weeks after deployment.
As previously described in detail (Keesing et al, 2022 (link)), we selected 24 residential neighborhoods that had reported high incidence of tick-borne diseases in Dutchess County in recent prior years. Neighborhoods consisted of ∼100 adjacent 1- and 2-family residences at moderate to high density, including their respective yards. Overall average property size was 0.19 ha. After a year of exhaustive efforts to recruit eligible households in each neighborhood to participate in the study, we enrolled a mean of 34% of properties in each neighborhood (range 24–44%).
Each of the neighborhoods was randomly assigned to one of four treatment categories, with six neighborhoods assigned to each category: (1) active TCS bait boxes and active Met52; (2) active TCS bait boxes and placebo Met52; (3) placebo TCS bait boxes and active Met52; and (4) placebo TCS bait boxes and placebo Met52. All participating properties in each neighborhood received the same treatment category. Placebo TCS bait boxes were identical to active bait boxes except that they contained no fipronil. Placebo Met52 consisted of water only. Participating households agreed not to deploy broadcast acaricides independent of our study throughout its duration.
Both products were used according to label instructions. TCS bait boxes, covered with galvanized steel shrouds (active and placebo), were deployed twice annually, in spring and mid-summer, at an average rate of 5.9 boxes per property (38/ha), at least 10 meters apart, preferentially in sites frequented by small mammals. Active Met52 was sprayed by truck-mounted high-pressure sprayers (GNC Industries, Inc.) at a concentration of 2.22 L per 378.5 L of water. Placebo Met52 (water only) was sprayed using the same truck-mounted sprayers at the same rate of 4 L of spray per 93 m2 at a pressure of 1.2–1.4 MPa. Spraying of active and placebo Met52 occurred twice each year, immediately before (April—early May) and during (late May–late June) the peak activity period for nymphal blacklegged ticks in this region (Ostfeld et al, 2018 (link)). Further details are provided in the supplementary online appendix of Keesing et al (2022 (link)) (
The study design was double-masked ( = “double-blind”), in that neither the members of participating households nor the team of researchers collecting data were aware of the treatment category of any of the neighborhoods. All data collection, entry, and compilation were conducted with the treatment categories remaining masked.
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