DOI: 10.5061/dryad.9w0vt4bnc
title: Environmental variables serve as predictors of the exotic and invasive Asian longhorned tick (Haemaphysalis longicornis Neumann): an approach for targeted tick surveillance

description: Since the 2017 discovery of established populations of the Asian
 longhorned tick, (Haemaphysalis longicornis Neumann) in the United States,
 populations continue to be detected in new areas. For this exotic and
 invasive species, capable of transmitting a diverse repertoire of
 pathogens and blood-feeding on a variety of host species, there remains a
 lack of targeted information on how to best prepare for this tick and
 understand when and where it occurs. To fill this gap, we conducted two
 years of weekly tick surveillance at four farms in Tennessee (three H.
 longicornis-infested and one without) to identify environmental factors
 associated with each questing life stage, to investigate predictors of
 abundance, and to determine the likelihood of not collecting ticks at
 different life stages. A total of 46,770 ticks were collected, of which
 12,607 H. longicornis and five other tick species were identified.
 Overall, abundance of H. longicornis was associated with spring and summer
 seasons, forested environments, relative humidity and barometric pressure,
 sunny conditions, and in relation with other tick species. The likelihood
 of not collecting H. longicornis was associated with day length and
 barometric pressure. Additional associations for different life stages
 were also identified and included other tick species, climatic variables,
 and environmental conditions. Here, we demonstrated that environmental
 variables can be useful to predict the presence of questing H. longicornis
 and provide ideas on how to use this information to develop a surveillance
 plan for different southeastern areas with and without infestations.
description: <strong><em>Tick
 Collection. </em></strong>Multiple tick species were collected
 at four privately owned farms in three eastern Tennessee counties. At each
 farm, 100 m transects were identified, representing three habitat types
 (forest, forest-field edge, and open pasture).We dragged for ticks along
 transects with a corduroy drag and checked the cloth every 10m along each
 transect for the presence of any tick species or life stage. All ticks
 found on the drag cloth were then stored in a tube containing 80% ethanol
 or RNA later; one tube was used for each transect. Larvae were collected
 with labeled lint roller sheets and stored in plastic bags. Once a site
 was identified and confirmed as infested with <em>H.
 longicornis</em>, we began to drag weekly from epidemiological weeks
 20–40 and then every other week for epidemiological weeks 41–19. Ticks
 were identified to species and life stage using a dissecting microscope
 and dichotomous keys.  <strong><em>Variable Selection
 and Acquisition. </em></strong>Potential environmental
 predictors of <em>H. longicornis</em> abundance (larval stage,
 nymph stage, females, and total collected) were considered for
 investigation. At the beginning of each transect, we used a Kestrel 3000
 pocket weather meter-heat stress monitor (Scientific Sales Inc,
 Lawrenceville NJ USA) to measure environmental conditions for each
 collection event (transect). These continuous variables included
 temperature, relative humidity, barometric pressure, and wind speed. We
 also identified categorical variables including farm, county, daylength
 (number of minutes between sunrise and sunset), season based on the
 equinox, habitat (identified at the site as edge, field, or forest),
 observed sun cover (cloudy, partly cloudy, full sun), and the number of
 habitat-sharing ticks of different life stages, sexes, and species
 obtained during collection. These included counts of larval stage, nymphal
 stage, males, females, and total collected for the species
 <em>Haemaphysalis leporispalustris</em> Packard,
 <em>Amblyomma americanum</em> L., <em>Dermacentor
 albipictus </em>Packard, <em>Dermacentor variabilis
 </em>Say, and <em>Ixodes scapularis </em>L.
 <strong><em>Descriptive
 Analysis. </em></strong>All statistical analyses were
 performed using STATA Version 16.1. Relative activity, similar to
 seasonality, of each <em>H. longicornis </em>life stage was
 calculated by determining the mean percent of ticks collected during each
 epidemiological week of the study. Normality of the continuous variables
 was assessed using the Shapiro-Wilk test, implemented in the STATA
 <em>swilk</em> command. The continuous variables included
 daylength, temperature, relative humidity, barometric pressure, wind
 speed, and total number of ticks collected. All assessed variables were
 non-normally distributed; thus, median and interquartile ranges were used
 as the measures of central tendency and dispersion, respectively.
 Distribution of the categorical variables (collection year, county, farm
 site, season, habitat, and sun cover at collection start) and their 95%
 confidence intervals were computed in (SAS/R). <strong><em>Investigation of
 Predictors of Abundance. </em></strong>A series of negative
 binomial models, each built in two steps, was used to investigate the
 predictors of <em>H. longicornis</em> abundance. First, the
 STATA <em>glm</em> command was used to investigate the
 univariable associations between each potential predictor and the outcome
 under a Poisson distribution, applying a relaxed alpha level of 0.10.
 Since there was evidence of significant overdispersion of all Poisson
 models (Pearson dispersion parameters for life stages: 1.79–173.82;
 <em>P </em>&lt; 0.05), as well as excess zero counts of
 the outcome variables, zero-inflated negative binomial (ZINB) models were
 fit to the data using the STATA <em>zinb</em> command. The
 Poisson and ZINB models were compared using their Akaike Information
 Criterion (AIC) values, with the model having the lowest value considered
 the best fitting model. Potential predictor variables with <em>P
 </em>&lt; 0.10 were considered for inclusion in the
 multivariable models. Potential predictor variables identified in either
 the negative binomial or logit portions of the univariable zero-inflated
 models were used to develop multivariable models for each <em>H.
 longicornis </em>life stage. The second step in model building involved
 development of a multivariable ZINB model for each age/sex category using
 a manual backwards elimination process using a critical alpha of 0.05. The
 coefficients of all variables were reviewed at each step for evidence of
 confounding. In situations where the removal of a variable resulted in a
 change of 20% or more in the coefficients of any of the variables in the
 model, the removed variable was considered a confounder and retained in
 the model, regardless of its statistical significance. No biologically
 plausible two-way interaction terms were identified for testing in the
 models. Incidence risk ratios (IR) and their 95% confidence intervals were
 computed for all variables retained in the final negative binomial part of
 the zero-inflated models. Odds ratios (OR) and their 95% confidence
 intervals were computed for all variables retained in the final logit part
 of the zero-inflated models.
description: # Environmental variables serve as predictors of the exotic and invasive
 Asian longhorned tick (*Haemaphysalis longicornis* Neumann): an approach
 for targeted tick surveillance
 [https://doi.org/10.5061/dryad.9w0vt4bnc](https://doi.org/10.5061/dryad.9w0vt4bnc) Multiple tick species were collected at four farms in three eastern Tennessee counties. At each farm, 100 m transects were identified, representing three habitat types (forest, forest-field edge, and open pasture). Ticks were identified to species and life stage using a dissecting microscope and dichotomous keys. While dragging we also collected environmental data including temperature, relative humidity, barometric pressure, and wind speed. We also identified categorical variables including farm, county, daylength (number of minutes between sunrise and sunset), season based on the equinox, habitat (identified at the site as edge, field, or forest), observed sun cover (cloudy, partly cloudy, full sun), and the number of habitat-sharing ticks of different life stages, sexes, and species obtained during collection. These included counts of larval stage, nymphal stage, males, females, and total collected for the species *Haemaphysalis leporispalustris* Packard, *Amblyomma americanum* L., *Dermacentor albipictus* Packard, *Dermacentor variabilis* Say, and *Ixodes scapularis* L. ## Description of the data and file structure Data are presented in an Excel file with the first tab providing the key for the definitions used in the second tab (data). Data are defined in the first tab. Missing data were coded as a period or a decimal. ## Code/Software no code is used, this is raw data