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Honors Theses

5-2016

Habitat Associations of Ixodes Scapularis (Acari: Ixodidae) in Syracuse, New York

Brigitte Wierzbicki

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Recommended Citation Wierzbicki, Brigitte, "Habitat Associations of Ixodes Scapularis (Acari: Ixodidae) in Syracuse, New York" (2016). Honors Theses. 106. https://digitalcommons.esf.edu/honors/106

This Thesis is brought to you for free and open access by Digital Commons @ ESF. It has been accepted for inclusion in Honors Theses by an authorized administrator of Digital Commons @ ESF. For more information, please contact [email protected], [email protected]. HABITAT ASSOCIATIONS OF IXODES SCAPULARIS (ACARI: IXODIDAE) IN SYRACUSE, NEW YORK

By

Brigitte Wierzbicki Candidate for Bachelor of Science Environmental and Forest Biology With Honors

May,2016

APPROVED Thesis Project Advisor: Af ak Ck M issa K. Fierke, Ph.D.

Second Reader: ~~ Nicholas Piedmonte, M.S. Honors Director: w44~~d. William M. Shields, Ph.D.

Date: ~ / b / I & r I II

© 2016 Copyright B. R. K. Wierzbicki All rights reserved. 111

ABSTRACT Habitat associations of Jxodes scapularis Say were described at six public­ use sites within Syracuse, New York. Adult, host-seeking blacklegged ticks were collected using tick flags in October and November, 2015 along two 264 m transects at each site, each within a distinct forest patch. We examined the association of basal area, leaf litter depth, and percent understory cover with tick abundance using negative binomial regression models. Models indicated tick abundance was negatively associated with percent understory cover, but was not associated with particular canopy or understory species. These results may assist park-goers and land managers in considering local risk factors for exposure to Jxodes scapularis and the diseases they transmit. IV

Table of Contents

ACKNOWLEDGEMENTS ...... i

INTRODUCTION ...... 1

METHODS ...... 2

Study Area ...... 2

Tick Collection ...... 3

Habitat Classification ...... 5

Analysis ...... 6

RESULTS ...... 6

DISCUSSION ...... 7

CONCLUSION ...... 9

LITERATURE CITED ...... I 0

APPENDIX ...... 11 V

ACKNOWLEDGEMENTS

I would like to thank my advisor, Dr. Melissa Fierke, for her help and support throughout this project. I am especially grateful to Nicholas Piedmonte, for his continual advice and assistance, and am thankful for an enjoyable field season. I would also like to thank all landowners for providing site access. 1

INTRODUCTION

Lyme disease (LD) is the most common tick-borne disease in North America, as well as one of the fastest growing infectious diseases in the United States. Onondaga

County, New York had 40 reported cases of LD in 2014 (CDC 2014). The blacklegged tick (lxodes scapularis Say) is the primary vector of LD to humans. BlackJegged ticks appear to be increasingly infected with Borrelia burgdorferi, the causative agent of LD, based on annual tick sampling at Green Lakes State Park (NYSDOH, unpublished).

These data indicate adult blacklegged tick infection rates have been climbing steadily from 31 % infected in 2007 to 56.3 % in 2014, while nymphal infection rates are up from

2.4% in 2008 to 26.9% in 2014 (NYSDOH 2015).

As of 2014, Green Lakes State Park was the sole site where tick abundance and infection in Onondaga County was quantified (NYSDOH, unpublished). However, a current SUNY ESF study intends to provide a fuller resolution of tick densities and disease prevalence across Onondaga County and within the City of Syracuse. This study involves tick sampling and disease testing at multiple public-use sites (Piedmonte, unpublished).

Environmental factors are critical to vector-borne infectious diseases. This is especially true for tick-borne diseases, as blacklegged ticks spend 98% of their life off a host (Brownstein et al., 2003). Jxodes scapularis abundance has been associated with multiple habitat features, including the presence of a shrubby understory (Ginsberg and

Ewing 1989), deep leaf litter (Schulze and Jordan 1995), and certain understory species.

In a habitat association study in Maine, Lubelczyk et al. (2004) found greater probability of tick abundance in the presence of Japanese barberry (Berberis thunbergii DC), 2 winterberry holly (/lex verticillata L. (Gray)), and Eurasian honeysuckle (Lonicera spp.), and a lower probability of tick abundance with the presence of eastern hemlock saplings

(Tsuga canadensis L. (Carr.)). Examining relationships between leaf litter and vegetative features as associated with tick abundance may aid in assessing potential disease risk beyond these sites and provides insight for tick management strategies based on manipulation of landscape characteristics.

This study complements an ongoing SUNY ESF study assessing tick densities and disease prevalence at multiple public-use sites within the City of Syracuse

(Piedmonte, unpublished). Elucidating tick habitat associations is critical to our understanding local sources of variation in tick abundance. Examining relationships between tick abundance, leaf litter depth and vegetative features (including dominant species, percent cover, and basal area) will aid in assessing potential disease risk beyond these sites and provides insight for tick management strategies based on manipulation of landscape characteristics.

METHODS

Study Area. This study was conducted within six public-use areas located in Syracuse,

New York (Fig. 1). Each area was partitioned into two forested patches, each minimally

100 m apart. Each forested patch, or site, was considered as a distinct experimental unit, as aduJt Jxodes scapularis have been found to disperse only an average of 1.8 in (Falco and Fish 1991 ). The dominant forest community of all sites was deciduous or mixed deciduous and coniferous forest types. 3

Eut Syracu ,

• •• • • • •• N

••

0 2km

Figure l. Markers indicate distinct forest patches within six study areas in Syracuse, NY.

Tick ColJection

Tick counts were obtained by flagging for questing adult Ixodes scapular is along a 264 m transect per site. Each site was sampled once, during peak adult tick season (Oct to Nov). Transects served as sampling units. Flagging occurred on days above 10 degrees

Celsius, between 1200 and 1700 hours. 4

Flagging was performed using a 1 m2 white flannel cloth. Total distance flagged was determined by calculating average distance traveled in 20 steps per investigator, and multiplying by the total number of 20-step intervals. Flags were pulled flush with leaf litter and understory vegetation and checked at each 20-step interval to remove ticks and debris (Fig. 2). Attached ticks were removed using forceps, and placed into 1.5 mL microcentrifuge tubes with 100% absolute ethanol. Ticks were identified to species and sorted by site, sampling date, habitat, and sex (Fig. 3).

Figure 2. Flagging for ticks; examining the flag for ticks. 5

Figure 3. Jxodes scapularis: Adult female, adult male, and nymph.

Habitat Classification

Habitat characteristics and dominant species were assessed and recorded at five

equidistant points along each transect. Leaflitter depth (cm to soil surface), understory

percent cover, and understory species were quantified within I m2 plots (Fig. 4)

established at each equidistant point. Canopy species and basal area measurements were

obtained at the same five points using a 10-factor wedge prism.

Figure 4. Example of I m2 plot established along transects. 6

Analysis

Leaf litter depth, understory percent cover, and basal area were averaged per transect. Association of these habitat characteristics with tick abundance were examined using negative binomial regression models. Canopy species and understory species data collected at each transect point were combined to represent each transect. Canopy species and understory species were independent factors and tick abundance was the dependent variable. These were modeled graphically to analyze variability per transect.

RESULTS

Plant species encountered varied by transect and by field site. There were 16 tree species encountered and 16 understory species. The most commonly encountered tree species were maple (Acer) species and the most commonly encountered understory species were buckthom (Rhamnus cathartica), maple (Acer) species, and lesser periwinkle (Fragaria vesca). Tick abundance did not appear to be associated with any particular canopy or understory species (Appendix 1).

Basal area at study sites varied from 34 to 180 m2/ha. Maple (Acer) species had the highest basal area across all sites, however, several sites had a high basal area of black cherry (Prunus serotina). Leaf litter depth ranged from 2.8 to 9.1 cm with the deepest encountered under maple (Acer) species. Percent cover of understory species varied from 7% to 47%. Buckthom (Rhamnus cathartica) exhibited the highest cover, though this varied greatly from site to site. Tick abundance was not significantly associated with site variables, including basal area (F 1, 11 = 0.95, p = 0.36) or leaf litter depth (F 1, 11 = 0.28, p = 0.51 ), however, it was negatively associated with percent cover 7

ofunderstory species (Fig. 8, F1 , 11 = 3.38, p = 0.037). Basal area, leaf litter depth, and understory percent cover were not correlated with each other (p > 0.05).

\ 0 N ' \ . ' ' \ \ It) • ',, \ .... \ C: • :, • '•, 0 '•, 0 0 ~- .,, ~ - ...... __ _ -~ --~- ...... __ _ I- It) ------·------· ··------_.., __ _ ·------• -----.. __ . ---- -. 0 • . .-··- .~=-:-::-:------·------~-· 0.1 0.2 0.3 0.4

Average Proportion of Understory cover

Figure 5. Negative binomial regression model indicating a negative association between tick abundance and understory percent cover (R2 = 0.25%, p = 0.037).

DISCUSSION

There did not appear to be a relationship between tick abundance and basal area, leaf litter depth, or canopy and/or understory species. These results differ from previous studies (Schulze and Jordan 1995, Lubelczyk et al. 2004), which found associations between tick abundance and leaf litter depth, canopy, and understory species. This study had a smaller sample size (n = 12) and may account for not finding the same results.

Another possibility is variation in canopy and understory species across sites, however, a comparable study by Lubelczyk et al. (2004) contained significantly more sampling sites with the same canopy and understory species. Our study was constrained in sample size, such that multiple species were only represented at an individual sampling site, which limited statistical analysis. 8

The negative association found between tick abundance and percent cover of

understory species is also inconsistent with prior research associating tick abundance and

presence of a shrub layer. Ginsberg and Ewing (1989) found a higher abundance of ticks with the presence of a shrub layer. Conflicting results from this study may be due to flagging error, considering adult Jxodes scapularis quest on understory species.

Herbaceous cover characteristics may reduce contact between the flag and questing ticks,

making it more likely for ticks questing on the ground to attach to the flag than ticks

questing on vegetation.

High variability in canopy and understory species composition across transects may have contributed to inconclusive results. Having more sampling sites containing

similar canopy and understory species would provide a stronger data set, as the minimal

overlap of species among sites limited statistical analysis. As such, this study should be

expanded while considering species composition as a factor for site choice. For comparing more directly to other studies, many factors would have to be considered, e.g., _...... ,._ _,... including non-forested areas fof collecting adult ticks, incorporating other tick life stages, etc., which may have provided results more consistent with prior studies. Utilizing different tick collection methodologies, e.g., CO2 trapping, counting ticks obtained from host species, is suggested.

It is expected that transects with oak-dominated habitats would be associated with

higher tick abundance, as they attract white-tailed deer, the preferred host of adult

blacklegged ticks (Ostfeld et al. 1995). More oak-dominated sites could be assessed to compare with the largely maple-dominated sites, thereby emphasizing importance of deer movement to oak-dominated sites during mast years, and a resulting shift in tick 9 populations. As this is a host-driven habitat change, it is of value to consider habitat associations including suitable vegetation and microclimate alone cannot fully describe I scapulari s distribution, and as of yet, no comprehensive predictive model of I scapularis abundance currently exists (Wilson I 998). However, on a smaller scale, variation in suitable vegetation has been associated with patchiness of/. scapularis distribution

(Schulze et a1. 1998). As such, descriptive models of local risk areas are helpful to provide more insights on local tick abundance.

Expansion of this study may fill in gaps to better associate local habitat characteristics with variable tick densities. Selected sites were within public-use areas, and thus high risk areas for human exposure to blacklegged ticks. Including more sites with similar plant compositions may result in significant relationships, thus aiding our understanding of associations between tick habitat and tick distribution and abundance in

Onondaga County, and assisting in decreasing LO incidence via manipulating local landscape features and educating the public about avoiding tick habitat.

CONCLUSION

This study was inconsistent with prior research, which may be in part due to variability across transects, limited sample size, and flagging differences. As Ixodes scapularis have found to be associated with a shrubby understory, deep leaf litter, and certain understory species, expanding this study may produce similar results.

Incorporating more replicate sites, multiple tick collection methodologies, and collection of ticks at different life stages may reduce variability. 10

LITERATURE CITED

Brownstein, John S., Theodore R. Holford, and Durland Fish. (2003). "A climate-based model predicts the spatial distribution of the Lyme disease vector Ixodes scapularis in the United States." Environmental Health Perspectives 111: 1152. Center for Disease Control and Prevention. (2014). "County-level Lyme disease data from 2000-2014." Falco, Richard C., and Durland Fish. "Horizontal movement of adult Ixodes dammini (Acari: Ixodidae) attracted to CO2-baited traps." Journal ofMedical Entomology 28.5 (1991): 726-729. Ginsberg, Howard S., and Curtis P. Ewing. ( 1989). "Habitat distribution of Ixodes dammini (Acari: lxodidae) and Lyme disease spirochetes on Fire Island, New York. "Journal ofMedical Entomology 26: 183-189. Lubelczyk, Charles B., et al. (2004). "Habitat associations of Ixodes scapularis (Acari: Ixodidae) in Maine." Environmental Entomology 33: 900-906. NYSDOH. (2015). "Green Lakes Deer Tick Testing." Vector Surveillance, Unpublished. Ostfeld, Richard S., et al. "Ecology of Lyme disease: habitat associations of ticks (lxodes scapularis) in a rural landscape." Ecological Applications ( 1995): 353-361. Piedmonte, N.P. (2015). "Influence of Landscape Characteristics and SmaJI Mammal Abundance on the Distribution of Ixodes scapularis and Prevalence of Borrelia burgdorferi Infection in Onondaga County, New York." MS Proposal, Unpublished. Schulze, Terry L., Robert A. Jordan, and Robert W. Hung. (1998). "Comparison of Ixodes scapularis (Acari: Ixodidae) populations and their habitats in established and emerging Lyme disease areas in New Jersey." Journal ofMedical Entomology 35: 64-70. Wilson, Mark L. (1998). "Distribution and abundance of Ixodes scapularis (Acari: Ixodidae) in North America: ecological processes and spatial analysis." Journal of Medical Entomology 35: 446-457. 11

Appendix 1. Presence/absence data for canopy and understory species per transect.

Transects: IA 18 2A 28 3A 38 4A 48 SA 58 6A 68 Canopy Species Maple Acer spp. 0

Oak Quercus spp. 0 0 0 0 0 0 0 0 0

Buck-thorn Rhamnus cathartica 0 0 0 0 0 0

Black walnutJug/ans nigra 0 0 0 0 0 0 0 0 0 0 0

Black locust Robinia pseudoacacia 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 Eastern cottonwood Populus deltoids

Black willow Salix nigra 0 0 0 0 0 0 0 0 0 0 0

Norway spruce Picea abies 0 0 0 0 0 0 0 0 0 0 0

Scotch pine Pinus sylvestris 0 0 0 0 0 0 0 0 0 0 0

Eastern white pine Pinus strobus 0 0 0 0 0 0 0 0 0

Sycamore Platanus occidentalis 0 0 0 0 0 0 0 0 0 0 0

Hickory Carya spp. 0 0 0 0 0 0 0 0 0

Beech Fagus grandifolia 0 0 0 0 0 0 0 0 0 0 0

Hemlock Tsuga canadensis 0 0 0 0 0 0 0 0 0 0 0

Eastern hophornbeam Ostyra 0 0 0 0 0 0 0 0 0 0 0 vlrginiana

Ash Fraxinus spp. 0 0 0 0 0 0 0 0 0 0 0

Understory Species Goldenrod Solidago spp. 0 0 0 0 0 0 0 0 0

Maple Acer spp. 0 0 0 0 0 0

Wood sorrel Oxalis acetosella 0 0 0 0 0 0 0 0 0 0 0

Buckthorn Rhamnus cathartica 0 0 0

Virginia creeper Parthenocissus 0 0 0 0 0 0 0 0 0 0 quinquefo/ia

Lesser periwinkle Vinca minor 0 0 0 0 0 0 0 0

Wild strawberry Fragaria vesca 0 0 0 0 0 0 0 0 0 0

Geranium Geranium robertianum 0 0 0 0 0 0 0 0 0 0 0

Poison ivy Toxidendron radicans 0 0 0 0 0 0 0 0 0 0 0

Oak Quercus spp. 0 0 0 0 0 0 0 0 0 0 0 12

Hickory Carya spp. 0 0 0 0 0 0 0 0 0 0 0

Ash Fraxinus spp. 0 0 0 0 0 0 0 0 0 0 0

Carexspp. 0 0 0 0 0 0 0 0 0 0 0

Rubusspp. 0 0 0 0 0 0 0 0 0 0 0

Violet Viola spp. 0 0 0 0 0 0 0 0 0 0

English ivy Hedera helix 0 0 0 0 0 0 0 0 0 0 0

Tick Count 3 9 2 0 21 16 13 2 14 0 0

Number indicates public-use area, lerter indicares sire.