Survival of larvae and nymphs of Ixodes scapularis Say (Acari: Ixodidae) in four habitats in Maryland

7 Pages·2003·2.1 MB·

by  J F Carroll

PROC. ENTOMOL.SOC. WASH.
lO.'^d),2003.pp. 120-126
SURVIVAL OF LARVAE AND NYMPHS OFIXODES SCAPULARIS SAY
(ACARI: IXODIDAE) IN FOUR HABITATS IN MARYLAND
J. F. Carroll
U.S. Department of Agriculture, Agricultural Research Service, Parasite Biology, Ep-
MD
idemiology and Systematics Laboratory, Beltsville, 20705, U.S.A. (e-mail:
[email protected])
—
Abstract. Host-seeking and fed larvae and nymphs of the blacklegged tick, Ixodes
scapitlaris Say. were placed in mesh packets and in vials in the leaflitteron the floorof
mixed deciduous forest, Virginia pine-.southern red oak forest, and white pine plantations
with and without Nepal microstegium, Microstegiwn vimineum (Trinius) A. Camus. An
introducedshade-tolerantgrass, Nepal microstegium, isexpandingitsrangenortheastward
into areas densely populated with /. scapukiris. As determined by flag sampling, the
density of host-seeking nymphs at the Virginia pine sites was much lower than in the
other habitats. None of the four habitats appeared to be consistently more favorable or
unfavorable for the survival ofconfined fed and unfed /. scapukiris larvae and nymphs.
More unfed nymphs survived in vials than in packets in Virginia pine and white pine
with Nepal grass sites. Fed larvae and nymphs tended to survive the summer better than
unfed ticks.
Key Words: blacklegged tick, immature stages, Nepal microstegium
In the United States, mostcasesofLyme one region to another independent of the
diseaseoccurin an areafromsouthernNew type of microhabitat (Bertrand and Wilson
England through the mid-Atlantic states 1997). Extreme temperatures and low rela-
(Spielmanetal. 1985)withMarylandasthe tive humidities are harmful to /. scapukiris
southernmost state with a significant Lyme (Stafford 1994, Vandyk et al. 1996). Gins-
disease problem. The blacklegged tick, Ix- berg and Zhioua (1996) found that /. sca-
odesscapukiris Say, the principal vectorof pukiris nymphs had a greater survival rate
the agent causing Lyme disease, is also in- in deciduous forest compared topine forest
volved in the transmission ofthe agents of on Long Island, New York. Lord (1993)re-
babesiosis and human granulocytic ehrlich- ported high mortality ofunfed/. scapukiris
iosis (Spielman et al. 1985, Dumler and nymphs in New York. In Maryland, 64-
Bakken 1995). Off-host survival offedand 70% of fed female /. scapukiris placed in
unfedticks is affectedby avarietyofbiotic leaflitter in a deciduous forest survived to
and abiotic factors, such as natural enemies oviposit at least some eggs (CaiToll 1996),
(e.g., predators, pathogens) and microme- but little is known about the survival of
teorological conditions (e.g., relative hu- free-living larvae and nymphs.
midity)(DanielandDusbabek 1994).These In Maryland, mixed deciduous forests
factors seem to be associated with micro- are a common natural habitat, varying in
habit,butdifferencesinsurvivalofflat(un- composition of dominant plant species ac-
fed) /. scapukiris nymphs may vary from cording tosoil type,drainageandotherfac-
VOLUME 103. NUMBER 1
tors. Blacklegged ticks are typically found Nepal grass, and white pine plantations
in these deciduous woodlands in Maryland without Nepal grass.
(Schmidtmann et al. 1994, CaiToU and Kra- Materials and Methods
mer 2001). Often, on well-drained soils
practically contiguous with the deciduous The deciduous forest study sites were lo-
foreststhere are standsofVirginiapine. Pi- cated at Loch Raven Reservoir. Baltimore
misvirginiana Miller,andsouthernredoak, County, Maryland, as were the white pine
Querciisfalcata Michaux. In central Mary- plantingswithandwithoutNepalgrass.The
land, white pine, P. strobiis L., does not Virginia pine-southern redoak forests were
occur naturally (Elias 1980) but is some- located in the U. S. Fish and Wildlife Ser-
times planted as ornamental or in mono- vice's Patuxent North Tract in adjoining
cultures as a form of reforestation. Black- Anne Arundel County. The deciduous for-
legged ticks also occur in the pine-domi- est was dominated by tulip tree, Liriodeii-
nated habitats. White-tailed deer, Odoco- dron tulipifera L., red maple.Acer rulyrum
iU'iis virgiiuaniis (Zimmermann). and other L.. hickory. Carya sp.. and black cheny.
important hosts of /. scapukiris readily Primus scrotiiui Ehrhart. Understory vege-
move among all three habitats. Nepal mi- tationwasgenerally sparseinthedeciduous
crostegium, Microstegiuni vimineum (Tri- woods, with some ferns and Nepal grass
nius) A. Camus (Poaceae), is a shade-tol- present. Leaf litter in these deciduous for-
erant, non-native species of annual (some- ests was notably shallow,andin someplac-
times perennial) grass. Since being intro- es virtually gone by mid-late summer, per-
duced intoTennesseeover80yearsago,M. haps due to the abundance of earthworms
vimineum has attained the status of an in- thatwereobserved. Incontrast, leaflitterin
vasive weed in the U. S., while expanding trheemaViinregdini=a10picnem-sdoeuetph.erFnewredotohaerksfpoerceisetss
its range northeastward into Maryland.
New York, and New England (Hunt and of trees were present in these woods, and
Zaremba 1992, Redman 1995. Ehrenfeld Sbmliuleab.exrrsipe.s,,weVarcecicioimiummonsp.i,natnhedugnrdeeernsbtroireyr..
1999). Nepal microstegiumhasexperienced
The white pine plantations were virtually
explosive distributional growth in Mary- monocultures, with ferns and Nepal grass
land since the 1980s (Redman 1995). In ar- being the principal understory species.
eas around Loch Raven Reservoir, Balti- For each of the four types of habitat,
more County, where there are extensive three sites (>0.8 km apart) were selected
dploamnitnianngstoufnwdheirstteopriynep,laMn.tvsipmeciineesu,mciosvetrh-e e(Fnicge.o1f)./.Eascchapsuiltaerwisasbysafmlpalgegidnfgorwitthhepar0e.s5-
ing considerable surface area and attaining by0.5 mflannelcloth(cribclothcontaining
heights of ==0.3 m. Ixodes scapukiris is a rubber laminate) 5 times for30 sec while
abundant in these white pine and adjacent walking slowly. At each ofthe three sites,
deciduous woodlands (Carroll, unpublished confined ticks were placed in the leaflitter
data). Nepal grassformssprawlingcolonies (where looselitteradjoinedcompactedlitter
that might provide shaded, humid refugia or soil) at each ofthree locations, with the
for larvae and nymphs of/. scapularis and exception of unfed larvae, which were
enhance their survival during late spring placed at one randomly selected location at
and summer. The grass dies and collapses each site in 1999. At each site each group
in the fall. The purpose of this study was ofticks was placed >10 mfromthe nearest
to obtain preliminary information on the group of conhned ticks. The location of
survival of fed and unfed /. scapularis each group was marked with a flag. Unfed
nymphs in the deciduous forest. Virginia and fed larvae and nymphs of/. scapularis
pine-oak forest, white pine plantations with were placed at these locations in 1999 and
PROCEEDINGSOFTHEENTOMOLOGICALSOCIETYOFWASHINGTON
Habitats
Whitepine/
Whitepine Virginiapine
Nepalgrass
CA ABC
BC AB
Sites A B C
Vials/ 12 3 12 3 123 123 123 123 123 123 123 123123 123
packets
Fig. L Foreach of4 types ofhabitiit, unfed and fed larvae and nymphs confined in nylon packets orin
vials were placed in leaflitterat 3 sites (designated here as A. B and C). At each site the packets and vials
wereplacedat3markedlocations(designatedhereas 1. 2 and3) ^10niapart.
2000 when free-living ticks were in the ofthe three locations (chosen randomly) at
same stage of development. Unfed larvae each ofthe three sites foreach habitat, one
and nymphs were collected from the held, packet or vial containing ticks was distrib-
placed in plastic snap-cap vials and main- uted to each location at each site. Nymphs
tained at 24-25° C, R. H. =97%, and nat- were placed out in late spring toearly suin-
ural photoperiod. Fed larvae and nymphs mer.andlarvaeinAugust. Unfedtickswere
were allowed to engorge on white rats in removed from the field and checked for
accordance with an approved USDA. ARS, mortality neartheendofthenaturalactivity
BeltsvilleAgricultural ResearchCenter, lA- periods forlarvae and nymphs (lateAugust
CUC protocol. Within 4 d after dropping toSeptember). Fedtickswerecheckedafter
from a rat, the fed larvae and nymphs were the time that individuals ofthe same stage
placed in nylon packets to be distributed at in nature should have molted into the next
the study sites. The packets were of 82 by life stage. Standard errors were calculated
82meshpercm-foldedoncetoformarath- for surviving ticks by habitat. Mean num-
er flat ~2 by 5 cm rectangle sealed on two bers ofticks in surviving vials and packets
sides by adhesive applied with a glue gun. were compared using Student's t-test.
Oncetheticks were placed insidethe pack-
et, the fourth side was folded over and RE.SULTS
closed as securely as possible with a bull- At least one nymph or adult of /. sca-
dog clip. In 1999. 10 unfed larvae. 5 fed piilaris was foundby flaggingatall butone
larvae, 6 unfed nymphs, and 3 fed nymphs of the study sites where ticks were placed
were placed in each packet. The following (Table 1). However, the Virginia pine-oak
year 8 unfed larvae, 6 fed larvae. 3 unfed habitat contained few /. scapiilaris. The
nymphs, and 3 fed nymphs were placed in summer of 1999 and the fall of2000 were
each packet. In 1999, unfed nymphs (6 per unusuallydry. whereasthesummerof2000
vial) were placed in plastic snap-cap vials was wet. In 1999, unfed larvae survived
(3 dram) with a0.8cmdiameterhole inthe poorly in all habitats (s43%), butespecial-
cap and nylon cloth covering the mouth of ly so in the deciduous forest (1%). which
the vial. Except in 1999, when one packet had significantly fewer (P = 0.004) survi-
containing unfed larvae was placed at one vorsthantheVirginiapine-southernredoak
VOLUME 105.NUMBER I
Table I. Numbersof/. sccipnlarisnymphsandadultscapturedbyflagging.5timesfor30secwliilewalking
slowlyateachstudy sitejustbeforethe firstpacketsoftickswereplacedinthe leaflitter.
Virgil
PROCEEDINGSOFTHEENTOMOLOGICALSOCIETYOFWASHINGTON
Table3. Numbersofunfedandfednymphsof/. scapularissunivingineachofthe4habitats. Meansper
locationonfollowingline:percentageoftickssurvivingineachhabitatinparentheses.
VOLUME 105, NUMBER 1
thereby avoiding some deleterious situa- LiteratureCited
tions (Carroll and Schmidtmann 1996). Al- Bertruiid.M.R.andM.L.Wilson. 1997.Microhabitat-
though fed larvaeand nymphs lackthe mo- independentregionaldifferencesinsurvivalofun-
bility of their unfed counterparts, much fedIxodesscapiilarisnymphs(Acari;Ixodidae)in
higher percentages of fed than unfed ticks Connecticut. Journal ofMedical Entomology 34:
167-172.
surIvnivtheedliantebostuhmmyeearrs.of 1999, an unknown CaiToIllx.odJe.sFsca1p9i9i6l.ariSsuravnidvortshehiirpeogfgsenignorageldeaffelmiatlteer
person removed all the flags marking the microhabitatinMaryland.EntomologiaExperien-
positions ofthe tick packets from one open talisetApplicata78: 349-331.
white pine site and a nearby white pine site Camill.J.FandM.Kramer.2001.Differentactivities
and footwear influence exposure to host-seeking
with Nepal grass. Despite written descrip- nymphs of Ixodes scapularis and Amhiyomina
tions of the locations ofthe packets, some aiiiericaniim(Acari:Ixodidae).JournalofMedical
were not found. A few other packets, per- Entomology38: 596-600.
haps removed by rodents or birds, were Carroll.J. E and E. T. Schmidtmann. 1996. Dispersal
neverrecovered. Somepackets,whichwere oadfubltlsacaktletghgeedwotoidcks-(pAacsatriu:reLxiondtiedrafaec)e.nyJmouprhnsalanodf
recovered, were found to have holes Medical Entomology 33: 554-558.
through which all the ticks escaped. These Daniel, M. and F Dusbabek. 1994. Micrometeoro-
losses may have reduced someoftheantic- logicalandmicrohabitatfactorsaffectingmain-
ipated discriminating power of the study, tesenainncteheanednvdiirsosnemmeinntat,iopnp.of91ti—c1k3-8b.orInnedSiosneeans--
but enough packets were recovered to de- shine. D. E. and T. M. Mather, eds. Ecological
tect any gross differences and some more Dynamics of Tick-Borne Zoonoses. Oxford,
subtle differences in tick survival among New York.
the habitats. Dumler. J. S. andJ. S. Bakken. 1995. Ehrlichial di.s-
easesofhumans: emergingtick-borne infections.
In conclusion, even though the study Clinical InfectiousDiseases20: 1102-1110.
took place during a unusually dry summer Ehrenfeld,J. G. 1999. A rhizomatous, perennial form
and a wet summer, none ofthe habitatsap- of Microsiegiiiiu viinineiim (Trin.) A. Camus in
peared obviously more favorable or unfa- New Jersey. Journal ofthe Torrey Botanical So-
vorableforsurvivalofconfinedfedandun- Elias.ciTe.tyS.12169:803.52T-h3e58C.ompleteTreesofNorthAmer-
fedlarvaeandnymphsof/. scapiilaris. Fur- ica: Field Guide and Natural History. Van Nos-
ther comparative sampling of host-seeking irandReinhold,New York,948 pp.
/. scapiiluris in Virginia pine-southern red Ginsberg, H. S. and E. Zhioua. 1996. Nymphal sur-
oak and other Maryland habitats is needed. avinvdalAmahndiyhoambiitnaatdaimsetrriibcuatniioinmoftiIcxkosde(Ascasrcaip:iiIlxaordi-s
idae)onFireIsland,NewYork,USA.Experimen-
Acknowledgments tal andAppliedAcarology20: 533-544.
Hunt. D. M,. and R, E. Zaremba. 1992. The north-
I thank Gene ScarpuUa, Reservoir Natu- eastward spread ofMicrosti'f;iiini vimineiim (Po-
ral Resources Office. Environmental Ser- aceae) into New York and adjacent states. Rho-
dora94: 167-170.
vices Division. City of Baltimore. Depart- Lord,C. C. 1993. MortalityofunfednymphalIxodes
mentofPublicWorks. BureauofWaterand damniini(Acari:Ixodidae)infieldexclosures.En-
Waste Water, Eldersburg, MD, for his co- vironmentalEntomology22: 82-87.
operation and for encouraging interest in Redman.D.E. 1995.Distributionandhabitattypesor
Nepal microstegium [Microstegium vimineiim
tphreesNsepmaylgmriactriotsudteegtioumKepnrnoebtlehm.YoIuanlgsoaenxd- C(Torliun.m)biCaa.mCuass]tainneaMa60r:yl2a7n0d-2a7n6d.the District of
Eli Miramontes, USDA, ARS, Parasite Bi- Schmidtmann. E. T,J. F Carroll, and W. J. E. Potts.
ology, Epidemiology and Systematics Lab- 19*^)4. Host-seeking of black-legged tick (Acari:
oratory, Beltsville. MD, fortheirassistance iInxtoedrifdaacee.)nJyomurpnhaslaonfdaMdeudltiscaaltthEentwooomdosl-opgaystu3r1:e
in making the packets used for confining 291-296.
the ticks. Schul/e,T. L.. R. A. .lordan. and R. W. Hung. 1998.
:
126 PROCEEDINGSOFTHEENTOMOLOGICALSOCIETYOFWASHINGTON
Comparison of Ixodes scapiilaris (Acari: Ixodi- humidities. Journal of Medical Entomology 31
dae) populationsandtheirhabitats inestablished 310-314.
andemergingLymediseaseareasinNewJersey. Vandyk,J.K.,D.M.Bartholomew,W.A.Rowley,and
Journa] ofMedicalEntomology35: 64-70. K. B. Piatt. 1996. Survival ofIxodes scapularis
Spielman, A.. M. L. Wilson,J. F.Levine.andJ.Pies- (Acari: Ixodidae) exposed to cold. Journal of
man. 1985.EcologyofIxodesdammini-bornehu- MedicalEntomology33: 6-10.
manbabesiosisandLymedisease.AnnualReview Yuval, B.andA.Spielman. 1990. Durationandregu-
ofEntomology30:439-460. lationofthedevelopmentalcycleofIxodesdam-
StaffordHI. K.C. 1994. Survival ofminiatureIxodes mini(Acari: Ixodidae). Journal ofMedical Ento-
scapularis (Acari: Ixodidae) at different relative mology27: 196-201.