A SURVEY OF ARTHROPODS ASSOCIATED WITH GOPHER TORTOISE BURROWS IN MISSISSIPPI

13 Pages·1991·3.6 MB·English

by  Paul K Lago

Vol. 102.No. 1.January& February 1991
A SURVEY OF ARTHROPODS ASSOCIATED WITH
GOPHER TORTOISE BURROWS IN MISSISSIPPI^
Paul K. Lago^
ABSTRACT: Asurvey ofarthropods associated with gopher tortoise burrows in Miss-
issippi revealed the presence of seven burrow commensals: Chelyoxenus xerobatis
(Coleoptera; Histeridae); Aphodius troglodytes and Onthophagus polyphemi sparsisetosus
(Coleoptera:Scarabaeidae);Philonthusgopheri(Coleoptera:Staphylinidae);Eutrichotasp.
(Diptera: Anthomyiidae), Machimus n. sp. (Diptera: Asilidae) and Amblyomma tuber-
culatum(Acari:Ixodida:Ixodidae).Eutrichotasp.rankedfirstinabundance,followedbyP.
gopheri, O. polyphemisparsisetosus andMachimus n. sp. (although the primary sampling
method,avacuumapparatus,biasedabundancedatainfavorofsurfacedwellerswithin
burrows).Anadditional24specieswereconsideredtobeopportunistsintheburrows,and
seven morewereapparentlyaccidental.Amongthe non-commensalswere20speciesof
Coleoptera,five Hymenoptera.twoOrthoptera.twoLepidoptera and twoDiptera.
The gopher tortoise (Gopherns polyphemus Daudin) is a large, ter-
restrial turtle endemic to the southeastern United States, including
southeastern Mississippi. Except when foraging during mornings and
late afternoons of spring, summer and autumn months, the reptiles
spend most oftheir time within burrows they construct in sandy soil.
Theseburrowsareusuallyrathersimple,butmayexceedsevenmetersin
length (Hansen, 1963), and are used for several years. The relative per-
manencyoftheburrows,coupledwith thepresenceofunique resources
(tortoise dung, in particular) has resulted in the evolution ofa unique
fauna ofvertebrates and invertebrates that reside with the tortoise.
Arthropodscompriseamajorpartofthegophertortoiseburrowfauna
and this group has received considerable attention in the past. Most
work done with this interesting assemblage, however, has been con-
ducted in Florida, and records for other areas are few and scattered.
Franz and Bryant (1982) summarized much information on tortoise -
habitat relationships and included a section entitled "Arthropods of
Gopher Burrows" (Woodruff, 1982a). Alist of39 species ofarthropods
associated with burrows in Florida was presented along with notes on
presumedrelationships(obligates,accidentals,etc.).Mistrey(1987)pre-
sented a considerably longer list (267 + species) and included much
information on biology of Florida burrow arthropods. He classified
burrow inhabitants as: a) commensals: obligate inquilines, basically
restricted tothe habitat provided bytheirhost, b)opportunists: species
'ReceivedAugust2, 1990.AcceptedOctober9. 1990.
^DepartmentofBiology,UniversityofMississippi,University, MS 38677
ENT.NEWS 102(1): 1-13,January&February, 1991
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using the burrow for cover, or feces for food, but found commonly in
other habitats, or consuming other types of feces and c) accidentals:
species normally occurring in other habitats and not regularly using
burrow resources.
Theburrowcommensalsaregenerallycoprophagous,parasiticonthe
tortoises,orpredaceousprimarilyonotherburrowarthropods.Asistrue
for any organisms with very narrow habitat requirements, any major
change in habitat availability could have devastating effects on the
speciesinvolved.Thestatusofthegophertortoisevariesfromthreatened
to endangered throughout its range; consequently, the status of the
obligate burrow inquilines is generally considered threatened or
endangered (Woodruff. 1982b), and with obvious good reason.
Howden and Cartwright (1963) described a new subspecies of
coprophagous scarab, (Onthophagus polyphemi sparsisetosus), collected
fromgophertortoiseburrowsinAlabama,FloridaandMississippi.The
Mississippi specimens, collected 6.5 miles south of Lucedale, George
County,representtheonlyknownrecordforatortoiseburrowinquiline
fromthestate.Aprimaryreason forthelackofrecordswould appearto
be lack of collecting effort. Recently (1983) Andrew F. Beck (pers.
commn.)useda modifiedvacuumtosampleseveralburrowsinHarrison
County. Also in 1983,1 excavated twoburrows in Harrison and George
counties, and throughout the early 1980's, set pit traps and blacklight
traps in areas with good gophertortoise populations. Noburrowinqui-
lines were collected during any of the above activity. The only insect
specimens I examined thatwere in anywayassociatedwith tortoises in
Mississippi was a series ofbeetles taken from tortoise droppings at the
mouth ofa burrow in Jones County, 21 August, 1985, by Robert Jones
and Jerry Watkins. Three species were represented: Myrmecaphodius
excavaticollis(Blanchard)(2 specimens) is an inquiline in fire ant nests
andisnotcoprophagous.Itspresenceinthisseriesisaccidental.^/aew/wj
platensis(Blanchard)(53 specimens)wasconsidered tobeaccidental in
tortoise burrows in Florida byWoodruff(1982a), but the presenceofso
manyinthisserieswouldseemtoindicatedamoremeaningfulrelation-
ship,andthiswillbediscussedlater.Thefinalspecimenintheserieswas
Ataeniuscylindrus Horn, a species normally associated with cattle dung
(Woodruff, 1973), and one that is not very common in Mississippi.
Recently there has been increased interest in "non-game" species by
state departments ofwildlife conservation, in particular those species
that may be threatened or endangered. The above-mentioned Ontho-
phagus was appropriately placed on the Mississippi list of species of
special concern, and during 1987, I conducted a status survey of O.
Vol. 102,No. 1,January&February 1991
polyphemi sparsisetosus in conjunction with a general survey of the
arthropod fauna ofgopher tortoise burrows in the state.
METHODS
The most obvious problems encountered during this study were: 1)
finding active tortoise burrows, and 2) sampling the arthropod fauna
withintheburrows.Thefirstproblemprovednotasdifficultasoriginally
anticipated. There is great interest in the status ofMississippi gopher
tortoise populations amongherpetologists andotherwildlife biologists
in the state. Several surveys, both formal and informal, have been con-
ducted (e.g. Lohoefener, 1982) and much ofthis information has been
compiled by the Mississippi Natural Heritage Program. The informa-
tionprovidedbytheHeritageProgramincludedlocalitiesofsupposedly
active burrows in all counties where the tortoise is known to occur.
Additionally, Harry Pawelczyk provided information on populations
within the DeSoto National Forest and several individuals assisted by
taking me to burrows ofwhich only they had knowledge. Although the
information provided by the Heritage Program and Pawelczyk was
invaluable in finding localities, the majority of actual field time was
spent making transects through the areas in an attempt to find active
burrows.Specificlocalitieswerechosenonthebasisofsuccesspotential
(largenumbersofactiveburrows)andonthebasisofdistribution(inall
counties within the range ofthe tortoise, including localities near the
margin ofthat range to get the broadest picture ofthe distribution of
arthropods encountered).
Sampleswerecollectedfromburrowsusingagas-poweredleafblower
thathadbeenmodifiedintoavacuum.Anadapter,with anin-linefilter,
was added to the air intake of the blower and a 1.25 inch diameter,
smoothborevacuumhoseattached.A30-foothoseenabledsamplingof
eventhelongestburrows.Theprocedureinvolvedsnakingthehoseinto
a burrow, attaching the hose to the vacuum, then slowly extracting the
hose with a twisting motion. The in-line filter caught debris and any
arthropods, while allowing sand to pass through. The filter was then
removed, its contents placed in an enamel pan and the athropods
collected. This method ofextraction has proven to be very efficient in
sampling burrows in Florida (A.F. Beck, pers. comm.; E.G. Milstrey,
pers. comm.), and is certainly less labor intensive than burrow exca-
vation. (It should be noted that excavadon of burrows has not been
allowed since gopher tortoises were placed on the Mississippi list of
endangered species.) Many additional specimens were obtained by
examiningtortoise feces found around burrowopenings.Occasionally,
pittrapsbaitedwithfreshtortoisefecesweresetnearburrows.Blacklight
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trapswere run in several colonies in an attempttocapturespecimensof
Copris gopheri Hubbard and Aphodius troglodytes Hubbard, burrow
inquilines occasionally attracted to light (Woodruff, 1973). Atotal of21
dayswasspentsearchingforandsamplingburrowsfrom7Maythrough
24 June, 1987. Voucher specimens have been placed in the insect
collection ofthe University ofMississippi.
Figure 1. Distributionofcollectinglocalitieswithintheapproximaterangeofthegopher
tortoisein Mississippi.
Vol. 102,No. 1,January&February 1991
RESULTS AND DISCUSSION
Duringthis study, light trappingwas ineffective in capturingburrow
inquiHnes. Although pit trapping did yield a few specimens ofcopro-
phagous species, no inquilines were collected using this method. The
vacuum method, however, was quite successful in capturing both
inquilines andotherburrowinhabitants,and unlessotherwise indicated,
comments belowrefertospecimenscollected in this manner. Usingthe
vacuum, samples were taken from 246 burrows at 48 localities in 12
counties.Activeburrowswere not found in Hancockcounty,buthistor-
ically tortoises are not common here (R. Lohoefener, pers. comm.).
Burrows were sampled in all other counties where tortoises occur in
Mississippi (Fig. 1). Table 1 presents locality data and the number of
burrows sampled at each site.
Table 1. Mississippi localitieswhereactivegophertortoiseburrowsweresampled
forinquilines.
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Vol. 102,No. 1,January&February 1991
Representativesof37 species in 11 families and fiveordersofinsects,
andone species oftickwerecollected from tortoiseburrows ortortoise
fecesduringthisstudy.Inthefollowingdiscussionofindividualspecies,
presumed relationships with the tortoise are indicated using the terms
definedbyMilstrey(1986): commensals,opportunistsoraccidentals(as
discussedabove).Admittedly,thedistinctionbetweenopportunisticand
accidental species, while obvious bydefinition, is somewhat subjective
for rarely encountered species. Consequently, some classification
changesmaybenecessaryinthefollowinglistasadditionalinformation
comes to light.
ANNOTATED LIST OF SPECIES
Coleoptera
Histeridae
ChelyoxenusxerobatisHubbard.Commensal.Localities5, 10, 12,20,26.26May-24
June.Specimenscollected-5.Thisspeciesburrowsintheflooroftortoisegalleriesandis
alsofoundintortoisefeces(Hubbard, 1894;YoungandGofT, 1939).Thelarvaeareappar-
ently predaceouson maggots feedingon tortoisedung(Hubbard, 1896). The five speci-
menscollectedweretakenfromwidelyscatteredlocalitiesindicatingarangeco-extensive
withthatofitshost.Thesmallnumberofindividualscollectedmaybeexplainedbythe
burrowinghabitsofthisspecies,orbythefactthatitissimplynotcommoninMississippi.
Burrowexcavationwouldbenecessarytodetermineifeitherorbothofthesestatementsis
true.
PhelisterrouzetiFairmaire.Opportunist.Locality24.15June.Specimenscollected-9.
This small series was taken from fresh tortoise feces near the mouth ofa burrow. The
species waspreviouslyunknowneastoftheMississippiRiver(R.Wenzel,pers.comm.)
Hydrophilidae
CercyonpygameusIlliger.Opportunist.Locality24. 15June.Specimenscollected- 1.
VariousspeciesoiCercyon,includingC.pygmaeus,arecommonlyfoundindung(Smetana,
1978).Thisspecimenwascollectedfromfreshtortoisefecesnearthemouthofaburrow.
Scarabaeidae
Aphodiusnibeolus (Beauvois). Accidental. Localities 29,34. 21,22June. Specimens
collected-2.AphodiusrubeolusiscommoninavarietyoftypesoffecesinMississippi,sothe
presenceofonlytwospecimensinburrowsamplesseemsbestdescribed asaccidental.
Aphodius stercorosus Melsheimer. Accidental. Locality48. 24 May. Specimenscol-
lected- 1.ThepresenceofthisgeneralistdungbeetlerepresentsthesamesituationasA.
rubeolus.Bothspeciesareverycommonherebutneitherwastakenfromreadilyavailable
tortoisefeces.
.
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Apbodius troglodytes Hubbard. Commensal. Locality 48. 15 June. Specimens col-
lected-3.Adultsandlarvaeofthisspeciesfeedonlyongophertortoisefeces(Woodruff,
1973).AlthoughtheyarecommoninFloridaburrows,specimensaremostoftenfoundin
the driest, sandiest areas (Milstrey, 1987). The single Mississippi location, in southern
WayneCounty,fitsthisdescriptionbetterthananyotherareavisitedduringthisstudy.All
specimensweretakenfromoneburrow.Sinceadultsremainassociatedwithtortoisefeces
(ratherthanburrowing),andsincefeceswereoftenvacuumedfromburrows,itsappears
thespeciesisveryrareinMississippi,andhasarangethatisnotco-extensivewiththatofits
host.
Ateeniuscy/indrusHorn.Opportunist.Localities12.16,21.22,25,32,36,44,47.19May-
24June.Specimenscollected-20.Specimenswerecollectedfromtortoisefeces,vacuumed
fromburrowsandtakeninapittrapbaitedwithfreshtortoisedung.Thisspeciesoccursin
cattlefecesandmustbeconsideredanopportunisthere,butthelargenumberofspecimens
collected and the wide range ofcollection sites indicated that tortoise droppings may
representa preferredopportunity.
AtaeniusfattigiCartwright.Accidental. Locality48. 15June.Specimenscollected- 1.
Typically found in cattle feces, and fairly common in Mississippi, the presence ofone
specimenoiA.fattigiin a vacuum sample isprobablybestdescribed as accidental.
Ataenius ovatulus Horn. Opportunist. Localities 23, 32. 15 and 22 June. Specimens
collected-3.Virtuallynothingisknownofthebiologyofthisrarespecies.Supposedlythey
donotusefecesasafoodsource(Woodruff1973).butIhavetakenspecimensinpittraps
baited with human feces and, during this study, three specimens were collected from
tortoisefeces.
Ataeniusplatensis Blanchard.Opportunist Localities 16,21,23,24,25. 15, 17and 18
June.Specimenscollected-127.Thisisacommon,widerangingspeciesthatusesavariety
offecesforfood.AlthoughWoodruff(1982a)consideredthistobeaccidentalintortoise
burrows, I collected 101 specimens from tortoise feces indicating a relationship better
described as opportunistic. Although the majority ofthese specimens were taken from
fecesnearthemouthsofburrows,severalwerecollectedfromfecalmassesvacuumedfrom
distalendsofburrows.
OathophaguspolyphemisparsisetosusHowdenandCartwright.Commensal.Local-
ities2,5,7,9,15,19,23.28,29,32,47.48.9May-24June.Specimenscollected-26.Adultsfeed
ontortoisefeces(Woodruff 1973).butlarvalhabitsremainunknown.SinceadultOntho-
phagus,ingeneral,burrowandburydungforlarvalfood,itseemslikelythatthevacuum
methoddidnotgiveagoodestimateoftherelativeabundanceofthisspecies.However,the
26specimens rankedsecondonlytoPhilonthusgopheriHubbard(Staphylindae)among
beetlecommensalscollected.Therangesofthebeetleandthetortoisearecoextensivein
Mississippi.Thiswastheonlycommensalcollectedoutsideburrows.Oneindividualwas
observedflyingintoaburrowonasunnyday(about2:00pm.80°F.).Thebeetleflewback
andforthacrosstheopeningtwoorthreetimes,eachtimeflyinglessdistanceandmoving
closertothehole,andfinallylandedabout20cmintotheburrow.Asecondspecimenwas
foundatthemouthofaburrowwhereitwasbeingsubduedbyfireants{Soienopsisinvicta
Buren).
Staphylinidae
AlenochoranotulaErichson.Opportunist.Locality24.15June.Specimenscollected-1
7
Vol. 102,No. 1.January&February 1991
Taken fromtortoise fecesatmouthofburrow.
Anotylus sp. Opportunist. Locality 24. 15 June.*Specimens collected -5. Taken from
tortoisefecesatmouthofburrow.
Falgariadissecta Erichson.Opportunist.Locality24. 15June.Specimenscollected-1.
Collectedwith theprecedingtwospecies.
GabronthusmgogoricusTottenham.Opportunist.Localities24,29. 15,21June.Speci-
mens collected - 5. Four specimens were taken from fresh tortoise feces near a burrow
mouth,the fifthwasvacuumed from aburrow.
Lithocaris sp.Opportunist. Locality24. 15June. Specimenscollected- 1.Taken from
tortoisefeces nearburrow.
Mycetoporus sp.Opportunist(?). Localities3,44. 8,23 May. Specimenscollected-2.
Bothspecimenswerevacuumed fromburrows.
PhilonthusgopheriHubbard.Commensal.Localities7,19,27,28,32,35,37,38.39,48.
May-24June. Specimenscollected-56.Thiswasthemostabundantofthecoleopteran
burrowcommensals, and its range coincides with the tortoise's here. Woodruff(1982a)
consolidatedthescatteredinformationonP.gopheri,butwithinthatmaterialtherewasno
informationastotheroleofthespecies intheburrows.
Philonthusspp.Twospecies(35specimens)werecollectedatlocation24fromtortoise
feces(15June)and an additional species(1 specimen)atlocation29from aburrow(21
June).Theseareprobablyopportunisticpredators.
Three additional unidentified species (6 specimens) within the Aleocharinae were
collectedfromtortoisefecesnearthemouthofaburrowatlocation24(15June).Probably
opportunistic predators.
Sincethe majorityofthe specimensofstaphylinids(notincludingPhilonthusgopheri)
were collected from tortoise feces, it seems logical that theywere feedingon organisms
thereandthattheyshouldbeconsideredopportunists.However,mostwerecollectedatthe
samelocality(24)andfromnearthesameburrow,unusualinthefactthatitwasshadedby
a dense shrub. "Accidental" may better describe the relationship between any ofthese
species andthegophertortoise,but furtherobservationsarenecessary.
Diptera
Anthomyiidae
Eutrichota sp.,probablyE.gopheri(Johnson).Commensal.Collectedatalllocalities
except3,6,and 18,throughoutsamplingperiod.Specimenscollected-75.Itisestimated
thatlessthan10%ofthefliesinvacuumsampleswereretained.Atripthroughthevacuum
hosewasfairlyhardonthesedelicateindividualsandconfirmationoftheiridentityawaits
collectionofgoodspecimensofmales.Thiswasthemostabundantcommensalencount-
ered.Adultsdominatedvacuumsamples from mostburrowsandlarvaewereverycom-
moninfreshtortoisefeces.Thenumberof"specimenscollected",whichdoesnotinclude
larvae,greatlyunderestimatesthenumberpresentinsamples.Whenthein-linefilterwas
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10
removed, most ofthe flies escaped. This was not considered to be a problem because
several stunned individuals were usually present. Many in the filterwerediscarded be-
causeofdamagecausedbythevacuumordeal.Isuspectthisspeciesistheprimarypreyfor
mostofthepredatoryburrowarthropods,butnoactofpredationwasactuallyobserved.
Asilidae
Machimusn.sp.Commensal.Localities7,28,35,45,47,48.21May-22June.Specimens
collected- 14.S.W.Bullingtonhasverifiedtheidentityofthisrobberflyasthespecieshe
andA.F.BeckaredescribingfromtortoiseburrowsinFloridaandGeorgia.Adultsrooston
theroofsofburrowsjustinsidetheentrance(within40cm).Onlyunderextremeharass-
mentcouldtheybeforcedtoleavetheburrow,andthentheyimmediatelyreentered.Most
specimenswerecollectedwhilethevaccumhosewasbeingwithdrawnfromaburrow.An
assistantwouldstandneartheentrance with anaerialnetandcapturespecimenswhen
theymadetheirbriefappearance.Onlythreespecimenswerecollectedwdththevacuum.
Althoughfourspecimensemergedfromoneburrowandthreefromanother,oneortwoper
burrow was the rule. Many more specimens were seen than were captured, including
individualsattwolocalitiesnotlistedabove.Theywerequickerthanwe.Therangeofthe
species here is co-extensive with that ofthe tortoise. According to Milstrey (1987), this
robber fly is predaceous on the anthomyiid fly, Eutrichotagopheri (Johnson), another
burrowcommensal.
Dolichopodidae
Hercostomussp.Accidental(?). Localities8,38,48.21 -26May. Specimenscollected-3.
Sphaeroceridae
Rachispoda sp.Opportunist(?). Locality44.8 May. Specimenscollected- 1.
Hymenoptera
Formicidae
All ofthe following species ofants are predaceous and are considered opportunistic
burrowinhabitants. On one occasion,an individual ofOnthophaguspolyphemisparsise-
tosus found at the mouth ofa burrowwas being attacked by many fire ants(Solenopsis
invicta).Althoughthebeetlewasstillalive,itwasincapableofcoordinatedmovementNo
otherinstanceofantpredation in aburrowwasobserved.
Apbaenogasterrudis Emery. Localities20,35.22,24June.Specimenscollected-5.
Cyphomyrmexrimosus(Spinola). Locality44. 19May. Specimenscollected- 1.
Iridomynnexpruinosus(Roger). Locality3.23 May.Specimenscollected- 1.
Solenopsis invicta Buren. Localities 3, 10, 15, 20, 22, 23, 35, 48. 23 May - 24June.
Specimenscollected- 18.