Ability of Three General-Use Pesticides To Suppress Nymphal Ixodes scapularis and Amblyomma americanum (Acari: Ixodidae).

We evaluated 3 over-the-counter pesticides for their ability to suppress host-seeking Ixodes scapularis and Amblyomma americanum nymphs. We applied liquid concentrate and granular formulations of Bayer Advanced Complete Insect Killer, Spectracide Triazicide Insect Killer, and Ortho Bug-B-Gon to forest plots using equipment available for purchase at retail home improvement outlets. All 3 liquid formulations provided rapid knockdown (≥98% control) of both species 1 day after application. Liquid Ortho Bug-B-Gone provided 100% suppression of I. scapularis throughout the 28-day postapplication period, while the other 2 liquid materials provided >95% control after 28 days. All liquid products also provided ≥95% control of A. americanum nymphs after 28 days. Granular formulations provided less consistent results, including lower 1-day knockdown rates for both species, due to very dry conditions, which prevented adequate release of the active ingredient from the carrier materials. After it rained in the study area, 7 and 14 days after application, we observed ≥99% suppression of both species. At 28 days posttreatment, control ranged between 87.5% and 95.6% for I. scapularis and between 89.3% and 94.4% for A. americanum . We show that these over-the-counter acaricides effectively suppressed 2 medically important tick vectors for at least 4 wk, and they provide a cost-effective tick control option for homeowners. In general, liquid formulations provided more rapid and greater and more consistent suppression than granular formulations, which may have implications for homeowner use of these products.

Willingness and ability of existing mosquito control and public health agencies in New Jersey to assume responsibilities for management of ticks and tick-borne disease.

We conducted surveys of New Jersey mosquito control and public health agencies to determine their willingness and ability to expand or create and maintain publicly funded tick and tick-borne disease (T/TBD) management programs. Nearly all (86%) of 21 county mosquito control agencies (MCAs) completed the survey, while only 25% of the 102 health departments (HDs) responded, probably reflecting traditional agency responsibilities. Although few of either group had formal programs, many were engaged in T/TBD-related activities. Many MCAs rated their ability to assume T/TBD responsibilities as high or moderate, while most HDs rated their capabilities as low. With the exceptions of lack of sustainable funding and possible legal constraints, the groups differed regarding perceived barriers to program creation and maintenance. Both groups envisioned comprehensive programs emphasizing public education, but program priorities differed between the groups. MCAs were willing to include most program activities, while HDs felt that some activities should be the responsibility of other agencies. MCAs were generally more familiar than HDs with tick control methods and while both groups would include control in a comprehensive program, both would limit control to public lands. Estimated program costs varied widely, probably reflecting responding agency size and complexity of envisioned programs. These results in a state with a system of existing agencies staffed by highly competent professionals suggest that more than simply additional funding (e.g., established guidelines for tick control and surveillance) is needed to create a network of practice necessary to address the growing incidence of TBD.

Detection of Babesia microti and Borrelia burgdorferi in host-seeking Ixodes scapularis (Acari: Ixodidae) in Monmouth County, New Jersey.

The etiological agents that cause human babesiosis (Babesia microti) and Lyme disease (Borrelia burgdorferi) share a common tick vector (Ixodes scapularis Say) and rodent reservoir (Peromyscus leucopus), but because the geographical distribution of babesiosis is more restricted than Lyme disease, it was not considered a nationally notifiable disease until 2011. Although recent studies have shown dramatic increases in the number of cases of babesiosis and expansion of its range, little is known about infection and coinfection prevalence of these pathogens in the primary tick vector. Of the 478 I. scapularis nymphs collected within six Monmouth County, NJ, municipalities between 2004 and 2006, 4.0 and 10.0% were infected with B. microti and B. burgdorferi, respectively, while 2.9% were coinfected. Analysis of the 610 I. scapularis adults collected during the same period yielded an infection prevalence of 8.2% for B. microti and 45.2% for B. burgdorferi, while 6.2% were coinfected. The potential public health importance of these findings is discussed.

Relative efficacy of high-pressure versus backpack sprayer applications of 2 natural product-based acaricides for control of host-seeking Ixodes Scapularis and Amblyomma americanum nymphs.

We evaluated the relative effectiveness of the natural product acaricide Essentria IC3 and the entomopathogenic fungal acaricide BotaniGard ES to suppress host-seeking Ixodes scapularis Say and Amblyomma americanum (L.) nymphs when applied with low-pressure backpack and high-pressure sprayers. Essentria IC3 applied by backpack sprayer out-performed high-pressure applications, while the opposite was true for treatments with BotaniGard ES. We were unable to demonstrate consistently greater efficacy using high-pressure applications, and neither of the acaricides or application methods provided substantial (>90%) levels of control at 7 days postapplication.

Community-based integrated tick management programs: cost and feasibility scenarios.

Numerous studies have assessed the efficacy of environmentally based control methods to suppress populations of the blacklegged tick (Ixodes scapularis Say), but few of these estimated the cost of control. We estimated costs for a range of tick control methods (including habitat management, deer exclusion or population reduction, broadcast of acaricides, and use of host-targeted acaricides) implemented singly or in combination and applied to a model community comprising 320 residential properties and parklands. Using the high end for cost ranges, tick control based on a single method was estimated to have mean annual costs per household in the model community ranging from $132 for treating only forest ecotone with a broadcast synthetic acaricide to kill host-seeking ticks (or $404 for treating all residential forested habitat) to >$2,000 for deployment of bait boxes (SELECT TCS) across all residential tick habitat to treat rodents topically with acaricide to kill infesting ticks. Combining different sets of multiple methods in an integrated tick management program placed the annual cost between $508 and 3,192 annually per household in the model community, underscoring the disconnect between what people in Lyme disease endemic areas say they are willing to pay for tick control (not more than $100-150 annually) and the actual costs for tick control. Additional barriers to implementing community-based tick management programs within residential communities are discussed.

Efficacy of plant-derived and synthetic compounds on clothing as repellents against Ixodes scapularis and Amblyomma americanum (Acari: Ixodidae).

We conducted field trials to compare the relative repellent activity of two natural product compounds (nootkatone and carvacrol) with commercially available plant-derived (EcoSMART organic insect repellent) and permethrin-based (Repel Permanone) repellents against adult Ixodes scapularis Say and Amblyomma americanum (L.) (Acari: Ixodidae) by using treated coveralls. One day after treatment, nootkatone and carvacrol provided 100% repellency of I. scapularis adults, with nootkatone maintaining complete protection through 3 d, whereas carvacrol showed steadily declining repellency against I. scapularis during the 7-d course of the trials. Nootkatone was at least as effective against host-seeking A. americanum as against I. scapularis through 3 d. Carvacrol provided little protection against A. americanum adults. Both natural compounds performed well initially in comparison with the commercial products. After 7 d, nootkatone was the most effective against both species followed in order of activity by Permanone, EcoSMART, and carvacrol. Nootkatone seems to have offer considerable potential as a clothing repellent against both I. scapularis and A. americanum.

Daily Variation in Sampled Densities of Ixodes scapularis and Amblyomma americanum (Acari: Ixodidae) Nymphs at a Single Site-Implications for Assessing Acarological Risk.

The public health challenge posed by tick-borne disease (TBD) has increased efforts to characterize the spatial and temporal distribution of ticks and associated pathogens to better focus tick control strategies and personal protection measures. We describe variability in nymphal Ixodes scapularis Say and Amblyomma americanum (L.) density derived from daily drag sampling at a single location in New Jersey over 4 yr and explore how observed differences in daily collections might affect the estimation of acarological risk. We found significant variability in the density of host-seeking nymphs that could suggest substantially different rates of human-tick encounters depending on sampling date, habitat, and ambient weather conditions. The spatial and temporal variability in the distribution of 2 sympatric tick species with different host preferences and questing strategies, suggests that to produce results that are comparable among sites across the area sampled, surveillance efforts may be limited to shorter collection seasons, fewer sites or less sampling effort (fewer plots or fewer visits) per site, and a geographic scope that minimizes the potential temporal and spatial biases indicated here. Our results illustrate that evaluation of models of tick distribution or relative acarological risk based on surveillance data requires a full description of the diversity of habitats sampled and the conditions under which sampling is performed. The array of factors that affect tick host-seeking and that could bias interpretation of sampling results emphasizes the need to standardize sampling protocols and for more caution when interpreting tick sampling data collected over large temporal and spatial scales.

Experimental use of two standard tick collection methods to evaluate the relative effectiveness of several plant-derived and synthetic repellents against Ixodes scapularis and Amblyomma americanum (Acari: Ixodidae).

We used two standard tick collection methods to test the relative effectiveness of two natural product compounds (nootkatone and carvacrol, classified as an eremophilene sesquiterpene and a monoterpene, respectively, that are derived from botanical sources) with commercially-available plant-derived (EcoSMART Organic Insect Repellent, comprised of plant essential oils) and permethrin-based (Repel Permanone) repellents against Ixodes scapularis Say and Amblyomma americanum (L.). Cloth drags were equally effective in sampling both species of host-seeking nymphs, whereas CO, traps attracted primarily A. americanum. All four repellents performed well on drags, with nootkatone and Permanone Repel (100% repelled through 14 d) slightly more effective than carvacrol and EcoSMART (90.7% and 97.7% repelled at 14 d, respectively) at repelling I. scapularis nymphs. Although the same trend in percent repellency was noted in the CO2 trap trial against both A. americanum nymphs and adults, EcoSMART outperformed Permanone in repelling A. Americanum nymphs after 14 d in the drag trial. Generally, the effectiveness of all repellents tested declined over time. The use of tick drags and CO2 traps was rapid, inexpensive, and easy to use in determining the relative effectiveness of repellents in the field.

Suppression of host-seeking Ixodes scapularis and Amblyomma americanum (Acari: Ixodidae) nymphs after dual applications of plant-derived acaricides in New Jersey.

We evaluated the ability of dual applications of natural, plant-derived acaricides to suppress nymphal Ixodes scapularis Say and Amblyomma americanum (L.) (Acari: Ixodidae) in a Lyme disease endemic area of New Jersey. An aqueous formulation of 2% nootkatone provided >90% control of I. scapularis through 7 d. Control declined to 80.9% at 14 d, and a second application was made that provided >95% control through the remaining 4 wk of the nymphal season. Nootkatone provided >90% control of A. americanum through 35 d postapplication. Applications of 2% carvacrol and EcoTrol T&O resulted in rapid knockdown of both tick species, but control declined significantly to 76.7 and 73.7%, respectively, after 14 d when a second application was made that extended control of both tick species to between 86.2 and 94.8% at 21 d. Subsequently, control declined steadily in all plots by 42 d postapplication except for I. scapularis in carvacrol-treated plots, where levels of control >90% were observed through 35 d. Of the three compounds tested, 2% nootkatone provided the most consistent results, with 96.5 and 91.9% control of I. scapularis and A. americanum through 42 and 35 d, respectively. The ability of plant-derived natural products to quickly suppress and maintain significant control of populations of these medically important ticks may represent a future alternative to the use of conventional synthetic acaricides. In addition, the demonstrated efficacy of properly-timed backpack sprayer application may enable homeowner access to these minimal-risk acaricides.

Geographical distribution and prevalence of selected Borrelia, Ehrlichia, and Rickettsia infections in Amblyomma americanum (Acari: Ixodidae) in New Jersey.

We used published accounts to describe the known statewide distribution of the lone star tick, Amblyomma americanum, in New Jersey and field surveys to characterize the geographical range of A. americanum and selected A. americanum-transmitted pathogens in Monmouth County, the hypothesized northern limit of the species distribution. Ticks were collected using standardized methods from 50 widely dispersed public access areas within 18 municipalities to produce estimates of relative abundance among sites. Collected A. americanum adults were stored at -80 degrees C until processed for DNA extraction. Individual ticks were subjected to polymerase chain reaction analyses to detect the presence of Ehrlichia chaffeensis, E. ewingii, Rickettsia amblyommii, and Borrelia lonestari. The range of A. americanum was generally limited to the southern half of New Jersey. Within Monmouth County, we collected A. americanum from 9 of 18 municipalities (50%) and 24 (48%) of the surveyed properties. We found at least 1 pathogen at 17 (70.8%) sites located within 6 of 9 municipalities, while all 4 target pathogens were detected in 5 of those 6 (83.3%) municipalities. The geographical distribution of A. americanum and its associated pathogens appeared to be restricted to the southern portion of the county. Possible factors governing the distribution are discussed.

Synthetic Pyrethroid, Natural Product, and Entomopathogenic Fungal Acaricide Product Formulations for Sustained Early Season Suppression of Host-Seeking Ixodes scapularis (Acari: Ixodidae) and Amblyomma americanum Nymphs.

We compared the ability of product formulations representing a synthetic pyrethroid acaricide (Talstar P Professional Insecticide), a natural product-based acaricide (Essentria IC3), and an entomopathogenic fungal acaricide (Met52 EC Bioinsecticide) to suppress Ixodes scapularis Say and Amblyomma americanum (L.) nymphs when applied following USEPA approved manufacturers' label recommendations for tick control using hand-pumped knapsack sprayers before the beginning of their seasonal activity period in the spring. We applied Met52 EC Bioinsecticide (11% Metarhizium anisopliae Strain F52) to five 100 m2 plots (10.6 ml AI/plot) in mid-April 2020. Two weeks later at the end of April 2020, we treated an additional five 100 m2 plots each with either Talstar P Professional Insecticide (7.9% bifenthrin @ 2.5 ml AI/plot) or Essentria IC3 (10% rosemary oil, 5% geraniol, and 2% peppermint oil @ 86.6 ml AI/plot). Weekly sampling of all plots through the end of June 2020 showed that both Met52 EC Bioinsecticide and Essentria IC3 failed to maintain a 90% suppression threshold for I. scapularis, compared to control plots, and required two additional applications over the course of the trial. In contrast, Talstar P Professional Insecticide suppressed 100% of I. scapularis nymphs and ≥96 and 100% of A. americanum nymphs and adults, respectively. Such pre-season applications of synthetic pyrethroids significantly reduce the early season acarological risk for exposure to host-seeking ticks as well as the frequency of acaricide applications.

Availability and Nature of Commercial Tick Control Services in Three Lyme Disease Endemic States.

In an update of earlier surveys conducted in Connecticut and New Jersey in the mid-1990s, an online survey of private commercial pest control firms engaged in residential tick control showed that the application of synthetic acaricides continues to be the primary method of control used. The carbamate and organophospate acaricides, previously the most commonly used against ticks, have given way to synthetic pyrethroids and, to a lesser extent, the use of natural product/organic acaricides. Typical costs for a single acaricide application today ($100-$200 for a 1 acre [0.4 ha] property) remain similar to those reported from the earlier surveys, although the frequency of applications and, therefore, also the overall annual cost has increased. The application habitats within residential properties, life stages targeted, and application equipment used have not changed appreciably since the mid-1990s. While most survey respondents expressed knowledge of natural product acaricides and Damminix Tick Tubes, many reported that they either did not employ or knew very little about other alternative tick control methods (including entomopathogenic fungus and topical application of acaricides to tick hosts via 4-Poster deer treatment stations or Select TCS rodent bait boxes). This suggests either a failure to adequately inform the pest management industry and their potential client base of the availability of alternate methods, and/or industry concerns about cost and effectiveness of the alternatives.

Artificial Accumulation of Leaf Litter in Forest Edges on Residential Properties via Leaf Blowing Is Associated with Increased Numbers of Host-Seeking Ixodes scapularis (Acari: Ixodidae) Nymphs.

We examined whether routine fall yard maintenance, specifically depositing leaves removed from lawns and landscaping along forest margins, may increase densities of nymphal Ixodes scapularis Say and Amblyomma americanum (L.) ticks within these managed areas. Leaf blowing activities in fall 2017 and 2018 on residential properties in New Jersey, United States, significantly increased leaf litter depth in managed edge areas (range = 259.8-352.8 mm) compared to unmanaged edges (77.6-188.0 mm) and adjacent forest (39.4-166.2 mm). Drag sampling conducted on 20 and 30 dates in spring 2018 and 2019, respectively, yielded ≥3-fold more I. scapularis nymphs in managed edge plots compared to natural edge and forest plots in both years. In 2018, we collected more A. americanum nymphs from forest plots than from either natural or managed edge plots, but 2019 natural edge plots yielded the greatest number of the ticks. Nearly half of A. americanum adults were collected in forest plots in both years. Our data suggest that the acarological risk of human encounters with I. scapularis nymphs may be significantly greater in areas receiving an accumulation of leaves from leaf blowing or raking compared to adjacent unmanaged forest edges. This artificially elevated acarological risk can be mitigated if homeowners avail themselves of curbside leaf pickup or composting services offered by many municipalities or request that lawn/landscaping contractors remove collected leaves offsite, or at least to areas of less frequent use, rather than concentrating them along the lawn-forest edge.

Early Season Applications of Bifenthrin Suppress Host-seeking Ixodes scapularis and Amblyomma americanum (Acari: Ixodidae) Nymphs.

We assessed the efficacy of bifenthrin to suppress Ixodes scapularis Say and Amblyomma americanum (L.) nymphs when applied prior to the initiation of spring host-seeking activity versus when nymphs were already active. Treatment and control plots were sampled for host-seeking ticks every week from mid-April through June, and single occasion bifenthrin applications were done in different sets of treatment plots on 15 April, 29 April, 13 May, and 27 May. Ixodes scapularis nymphs and A. americanum nymphs and adults were effectively suppressed after each application, with at or near 100% suppression of all ticks being observed for up to 8-wk postapplication. Irrespective of the bifenthrin application date, the level of suppression of I. scapularis nymphs never declined below 70% during the study period. However, with the exception of the last application, the suppression of A. americanum nymphs decreased dramatically to below 25% by the conclusion of the trial. The results of this study demonstrated that preseason applications of bifenthrin can mitigate acarological risk of exposure to ticks throughout much of their spring peak activity period.

Precipitation and temperature as predictors of the local abundance of Ixodes scapularis (Acari: Ixodidae) nymphs.

Populations of Ixodes scapularis Say nymphs were surveyed at a Lyme disease- endemic area for 8 consecutive yr (1998-2005) to characterize annual changes in abundance. Precipitation and temperature were also monitored over the period 1998-2004 to determine their potential value as predictors of tick abundance. Although both parameters showed annual variation, no statistical differences in the annual abundance of I. scapularis nymphs were observed over the 8-yr period. Our results suggest that precipitation and temperature were not predictive of the abundance of I. scapularis nymphs.

Ability of two natural products, nootkatone and carvacrol, to suppress Ixodes scapularis and Amblyomma americanum (Acari: Ixodidae) in a Lyme disease endemic area of New Jersey.

We evaluated the ability of the natural, plant-derived acaricides nootkatone and carvacrol to suppress Ixodes scapularis Say and Amblyomma americanum (L.) (Acari: Ixodidae). Aqueous formulations of 1 and 5% nootkatone applied by backpack sprayer to the forest litter layer completely suppressed I. scapularis nymphs through 2 d. Thereafter, the level of reduction gradually declined to < or =50% at 28 d postapplication. Against A. americanum nymphs, 1% nootkatone was less effective, but at a 5% concentration, the level of control was similar or greater to that observed with I. scapularis through 21 d postapplication. Initial applications of 0.05% carvacrol were ineffective, but a 5% carvacrol formulation completely suppressed nymphs of both species through 2 d and resulted in significant reduction in I. scapularis and A. americanum nymphs through 28 and 14 d postapplication, respectively. Backpack sprayer applications of 5% nootkatone to the shrub and litter layers resulted in 100% control of I. scapularis adults through 6 d, but the level of reduction declined to 71.5% at 28 d postapplication. By contrast, high-pressure applications of 2% nootkatone to the litter layer resulted in 96.2-100% suppression of both I. scapularis and A. americanum nymphs through 42 d, whereas much lower control was obtained from the same formulation applied by backpack sprayer. Backpack sprayer application of a 3.1% nootkatone nanoemulsion resulted in 97.5-98.9 and 99.3-100% reduction in I. scapularis and A. americanum nymphs, respectively, at 1 d postapplication. Between 7 d and 35 d postapplication, the level of control varied between 57.1% and 92.5% for I. scapularis and between 78.5 and 97.1% for A. americanum nymphs. The ability of natural products to quickly suppress and maintain significant control of populations of these medically important ticks at relatively low concentrations may represent a future alternative to the use of conventional synthetic acaricides.

Ability of Two Commercially Available Host-Targeted Technologies to Reduce Abundance of Ixodes scapularis (Acari: Ixodidae) in a Residential Landscape.

Host-targeted technologies provide an alternative to the use of conventional pesticide applications to reduce the abundance of Ixodes scapularis Say, the vector for an array of tick-associated human diseases. We compared the ability of Damminx Tick Tubes (Damminix) and SELECT Tick Control System (Select TCS) bait boxes to control host-seeking I. scapularis nymphs in a wooded residential environment. Small mammals accepted and used Select TCS bait boxes with greater frequency compared to Damminix tubes over the course of the 2-yr trial. Nymphal tick infestation prevalence and intensity on captured mice and chipmunks provided no conclusive evidence of a treatment effect during May-June of both years. However, both treatments had a measurable effect on larval tick burdens in July-August and the magnitude of the effect was greater at the Select TCS-treated area and reflected the fact that Select TCS effectively treated chipmunks, while Damminix did not. Deployment of Damminix resulted in 27.6 and 20.3% control of questing nymphs in treated areas at 1 yr and 2 yr postintervention, while Select TCS bait boxes provided 84.0 and 79.1% control, respectively. The economics of residential tick control using these products in wooded residential landscapes is discussed.

Suppression of Ixodes scapularis (Acari: Ixodidae) following annual habitat-targeted acaricide applications against fall populations of adults.

Spring acaricide applications directed against nymphal Ixodes scapularis have been shown to be effective, but are perceived by the public as having significant adverse environmental impacts, particularly against nontarget organisms. Targeting the adult stage of I. scapularis in the fall would hypothetically result in indirect control of subsequent subadult stages while avoiding other arthropods that are typically inactive during this period. We demonstrate that single fall applications of deltamethrin for 3 consecutive years immediately reduced fall questing adults, while also rapidly reducing the abundance of all postembryonic stages. Deltamethrin applied to the shrub-layer vegetation resulted in levels of control between 97.1% and 100% at 7 days postapplication. Repeated applications against the reproductive stage of I. scapularis progressively reduced the abundance of larvae and nymphs in treated plots, reaching 91.4% and 100% by the conclusion of the study.

A historical snapshot of Ixodes scapularis-borne pathogens in New Jersey ticks reflects a changing disease landscape.

Historical specimens, when available, can provide new insight into the distribution and evolution of pathogens that may not be discernible from more recent samples. We used ticks collected from hunter-killed white-tailed deer in New Jersey in 2002 to examine the prevalence and distribution of four pathogens transmitted by Ixodes scapularis, the blacklegged tick. Infection with Borrelia burgdorferi sensu stricto, Babesia microti, and Anaplasma phagocytophilum (the agents of Lyme disease, human babesiosis, and human granulocytic anaplasmosis, respectively) was highest in the Coastal Plain and lowest in the northwestern Skylands region. These patterns correspond well with the historically observed northward expansion of I. scapularis within New Jersey and the comparatively recent increase in human cases of these pathogens in the northern part of the state. Additionally, we provide evidence that Borrelia miyamotoi, a relatively new emerging pathogen and agent of relapsing fever, was widespread (though not common) throughout the state in 2002. Our findings highlight the need for enhanced awareness of tick-borne diseases other than Lyme and implementation of large-scale tick surveillance in endemic regions.

Effects of reduced deer density on the abundance of Ixodes scapularis (Acari: Ixodidae) and Lyme disease incidence in a northern New Jersey endemic area.

We monitored the abundance of Ixodes scapularis Say (Acari: Ixodidae) and the Lyme disease incidence rate after the incremental removal of white-tailed deer, Odocoileus virginianus Zimmermann, within a suburban residential area to determine whether there was a measurable decrease in the abundance of ticks due to deer removal and whether the reduction in ticks resulted in a reduction in the incidence rate within the human population. After three seasons, the estimated deer population was reduced by 46.7%, from the 2002 postfawning estimate of 2,899 deer (45.6 deer per km2) to a 2005 estimate of 1,540 deer (24.3 deer per km2). There was no apparent effect of the deer culling program on numbers of questing I. scapularis subadults in the culling areas, and the overall numbers of host-seeking ticks in the culling areas seemed to increase in the second year of the program. The Lyme disease incidence rate generated by both passive and active surveillance systems showed no clear trend among years, and it did not seem to vary with declining deer density. Given the resources required to mount and maintain a community-based program of sufficient magnitude to effectively reduce vector tick density in ecologically open situations where there are few impediments to deer movement, it may be that deer reduction, although serving other community goals, is unlikely to be a primary means of tick control by itself. However, in concert with other tick control interventions, such programs may provide one aspect of a successful community effort to reduce the abundance of vector ticks.