Mid-winter foraging of colonies of the pine processionary caterpillar Thaumetopoea pityocampa Schiff. (Thaumetopoeidae)

7 Pages·2003·4.5 MB·English

by  T D Fitzgerald

Journal
of
The Lepidopterists' Society
Volume 57 2003 Number3
JournaloftheLepidopterists'Societtj
57(3),2003,161-167
MID-WINTER FORAGING OF COLONIES OF THE PINE PROCESSIONARY CATERPILLAR
THAUMETOPOEAPITYOCAMPA SCHIFF (THAUMETOPOEIDAE)
T D. Fitzgerald
DepartmentofBiologicalSciences,StateUniversityofNewYorkatCortland,Cortland,NewYork13045, USA
AND
Xavier Panades I Blas
UniversityofBristol, DepartmentofEarthSciences,WillsMemorialBuilding,QueensRoad, Bristol,England
ABSTRACT. ThepineprocessionarycaterpillarThaumetopoeapityocampaSchiff. (Thaumetopoeidae)overwintersasanactivelarva.Field
recordingsmadeatourstudysiteinCatalonia(Spain) duringmid-wintershowthatthecaterpillarisremarkableinits abilitytolocomoteand
feedattemperatureswellbelowthoseatwhichtheactivityofmostotherinsectsiscurtailed. Coloniesinitiatedforagingboutsintheevening,
93.1 ±35.2minutesaftertheendofciviltwilightandreturnedtothenestthefollowingmorning,42.9 ±24.9minutesbeforetheonsetofcivil
twilight. Despiteanovernightmeanminimumtemperatureof3.8±0.25°Cduringthestudyperiod,caterpillarswereactiveeachnightanddid
notbecomecold-immobilizeduntilthetemperaturefellbelow-2°C. Duringthedaytime,thecaterpillarssequesterthemselveswithin their
nestsandonsunnydaysareabletoelevatetheirbodytemperaturesbyconductingheatfromthestructures.Themeandifferencebetweenthe
dailyhighandlownesttemperaturewas30.9±0.9°C.Themaximumnesttemperaturerecordedwas38°C. Salientfeaturesofthebiologyand
ecologyofT.pityocampaarecomparedtothoseofothercentralplaceforagersinanattempttoelucidatethefactorsthatmayunderlietheevo-
lutionofforagingschedulesinsocialcaterpillars.
RESUMEN. Laprocesionariadelpino,ThaumetopoeapityocampaSchiff.(Thaumetopoeidae),permaneceactivaduranteelinvierno.Los
registrosdecampoobtenidosenelpresenteestudioenCataluiia(Espafia),durantelapartemediadelinvierno,muestranqueestalarvaesasom-
brosaporsuhabilidadparadesplazarseyalimentarseatemperaturasmuypordebajodeaquellasalasquelaacthidaddelamayoriadelosin-
sectosesimpedida. Lascoloniasiniciansuperiododeforrajeoenlanoche,93.1 ± 35.2minutosdespuesdelapenumbracivilyregresanasus
nidosalamafianasiguiente,42.9±24.9minutosantesdeliniciodelapenumbracivil.Apesardequelatemperaturaminimadurantelanoche
enelperiododeestudiofuede3.8±0.25°C,laslarvasestuvieronactivascadanocheynoseinmovilizabanporelfriohastaquelatemperatura
descendiapordebajodelos-2°C.Duranteeldia,laslarvassemantem'andentrodesusnidos,dependiendodelahabilidaddeestasestructuras
paraabsorberlaenergiasolarparaelevarsutemperaturacorporal.Enelinteriordelosnidos,eldiferencialpromedioentrelatemperaturamax-
imayminimafuede30.9 ± 0.9°C. Latemperaturamaximaregistradadentrodelosnidosfuede38°C. Lascaracteristicassobresalientesdela
biologiayecologiadeestalarvaprocesionariasoncomparadasconlasdeotrasespeciesdeforrajeocentral,enunintentopordilucidarlasfac-
toresquesubyacenenlaevolutiondelospatronesdeforrajeodelarvassociales.
Additionalkeywords: processionarybehavior,trailfollowing,activitypatterns,thermalregulation.
Thaumetopoeapityocampa Schiff., thepineproces- ingthe establishmentoftheirpermanentnests (Fabre
sionary caterpillar, is distributed throughout much of 1916), there have been no studies ofthe foragingbe-
southern Europe where the larvae feed gregariously havior oflarvae in midwinter, nor are there any long
on the needles ofpine (Pinus spp.). Colonies develop term records offoraging behavior for any time ofthe
from egg masses of70 to 300 eggs (Dajoz 2000). The year. Ofparticularinterest is the question ofwhether
siblings at first build and abandon a series ofloosely the caterpillars forage on evenings when overnight
spun nests but in the third instar establish a perma- temperatures approachfreezing. Ofparallelinterestis
nentnestandbecome centralplace foragers (Halperin the rolethatthe nest mightplayin enablingthe cater-
1990). In Catalonia (Spain), the larval stage typically pillars to process food in their guts at low ambient
extends from August until April ofthe followingyear temperatures. Several investigators have made spot
and the caterpillars overwinter as active larvae. Al- measurements ofnesttemperatures andhavereported
thoughitis knownthatthelarvae feedatnightfollow- thatwhen irradiated bythe sunthe structures achieve
162 Journalofthe Lepidopterists' Society
temperatures as much as 17°C in excess ofthe ambi- diatedwith a250-Winfraredlampsituated0.5 m from
ent temperature (Breuer et al. 1989, Demolin 1969, the nests (Breuer & Devkota 1990, Fitzgerald & Un-
Breuer & Devkota 1990, Halperin 1990), but there derwood 2000). Temperature probes were inserted at
have been no continuous measurements of nest tem- the centers ofthe irradiated and shaded sides ofthe
peratures in midwinter. The recent availability of nests, approximately2cmbelowthe surface. Thetem-
small, portable dataloggers has made possible the un- perature ofeach nestwas measuredat 1 minute inter-
interrupted recording ofphysical and behavioral data vals for approximately 135 minutes after which the
heretofore not feasible in remote locations, and a de- heat sourcewas extinguished and additional measure-
tailed database ofecologically relevant aspects ofthe ments madeuntilthe nests cooledtoambienttemper-
foragingbehaviorofsocialcaterpillarshasbeguntoac- ature. Temperature measurementswereautomatically
cumulate (Fitzgerald et al. 1989, Fitzgerald & Under- writtentodataloggers (OnsetComputerCo., accuracy
wood 1998a, b, Ruf&Fiedlerinpress). Weundertook ± 0.2°C ) and the data downloaded with BoxCarPro
the present studyofthe pine processionaiycaterpillar Software (Onset ComputerCo.).
to addtothis database and, more specifically, toinves- Temperature measurementofnests atthe field
tigate the mid-winter foraging behavior ofthe insect. study site. The internal temperatures offive nests of
Wemonitoredboththedailytemperaturecycles ofthe the pine processionaiy were monitored in the field
nests and the foraging and resting cycles ofthe cater- from 17-26 February. Temperature probes were in-
pillars. sertedapproximately8cmbelowtheuppersurfacesin
areas ofnests occupied by caterpillars. Ambient tem-
Materials and Methods
peratures were measured in shaded areas near the
Study site. Studies ofnest temperature and colony study nests. Temperature data were recorded at 15
activitypatternswereundertakenduringFebruary2001 minute intervals as described above and the datalog-
inamountainousregionnearLaMoixeta, (BaixPenedes gers downloaded at 24 h intervals. Temperature
County), Catalonia(Spain) (41°21'N, 001°31'E), eleva- records foratotal of19 colony-dayswere collected.
tion approximately 400 m. The canopy of the study Daily activity patterns of field colonies. Daily
area consisted almost entirely ofpure stands ofPinus activitypatterns ofsevencolonies ofT. pityocampa oc-
lialepensis andP. pinea. curring on different trees were monitored with in-
Climate records. Seasonal climate records for frared activity monitors (Fitzgerald & Underwood
1999-2001 were obtained from die Catalonia Meteo- 2000) from 18-26 February. Records for atotal of26
rology Service. Data are from Font-Rubi (1'Alt colony-dayswere collected. The monitorswereplaced
Penedes County, elevation 409 m) the nearestgovern- on branches bearing the major trunk trails of the
ment maintained weather station, approximately 8.5 colonies, approximately20cm from eachnest. Activity
km from the La Moixeta study site. The hot summers monitors were connected to event loggers (Onset
typical ofdie Mediterraneanclimaticzone are moder- computer Co.) which recorded the time ofdaywhen
ated by elevation at the La Moixeta site, and the diecaterpillarstriggeredthemonitors. Aresetdelayof
months of November through February are corre- five seconds was programmed into the recorders to
spondingly cooler with midwinter temperatures ap- minimizetheprobabilitythatasinglepassingcaterpil-
proaching,butonlyoccasionallyfallingbelow, freezing. lar would trigger the monitor more than once. Data
Orientation ofnests at the field study site. The were offloaded with BoxCarPro software at 24 hour
positions of157T. pityocampa nests relativetothecar- intervals. Colonies were also observed each evening
dinal compass points were plotted at the study site to with red-filtered light and again in the early morning
determineifthenests arepositionedtotakeadvantage to aid in the interpretation ofthe activity recordings.
ofsolar radiation. The nests occurred naturallyon ei- In reportingthe timeofonsetandtermination ofdaily
therP. lialepensis orP. pinea. Trees were divided into activityperiods, we ignored isolated earlystarters and
quadrants each centered about a cardinal compass di- stragglersbyconsideringcolonyactivitytohavestarted
rection andthepositionofeachnestonatreeassigned when the number ofcaterpillars moving past the de-
toone ofthe quadrants. tector reached 10 or moreper 15 minutes andtohave
Heat gain in nests undercontrolledconditions. endedwhen the number or returning caterpillars fell
Laboratory studies were conducted to determine how to fewerthan thatnumber.
nests gain and maintain heat when exposed to a radi- Statistical analyses. Statistical analyses as detailed
ant heat source. Four empty nests of different sizes below were conducted with SigmaStat and ProStat
weremaintainedin atemperaturecontrolledchamber statisticalsoftware. Nestorientationwasanalyzedwith
with an ambient temperature of6.0 ± 2.0°C andirra- Rayleigh's testforcirculardistribution (Zar 1974).
Volume 57, Number 3 163
80-, February20
February19
70
60
1200 2400
Time
Fig.3. TemperatureinsidethenestofacolonyofT.pityocampa
(gray) andambient temperature (black) recorded overa three day
period.
N S E W laboratoryshowedarapidincreaseininternaltemper-
Orientation(quadrant) ature on the irradiated side (Fig. 2). The larger nests
Fig. 1. Orientation ofnests ofT. pityocampa onpine trees at showed virtually no heat gain on the shaded sides
thestudysite.
whiletheshadedsides ofthesmallernestshadmodest
gains relative to the irradiated sides ofthe structures
Results
(Fig. 2). Temperature differentials betweenthe irradi-
Orientation ofnests at the field study site. Ap- atedandshadedsides ofthenests rangedfrom 29.3°C
proximately61% ofthe nests atthe studysitewere lo- in the larger nests to 13.2°C in the smaller. All ofthe
catedwithin the SE-SW (135-225°) quadrant on the nests cooled precipitously to ambient temperature
crowns oftrees. Nestswere non-randomlydistributed when the heatsourcewas removed (Fig. 2).
with a mean orientation of204 ± 6.8° (SE) (Rayleighs Diurnal fluctuation ofnest temperature in the
testofuniformity, p < 0.01, Fig. 1). field. On 19-23 and 25 February, skies at the study
Heatgaininnests undercontrolledconditions. site were largely cloud free. Four of our five study
Empty nests exposed to a radiant heat source in the nests were in open areas and were directlyirradiated
bythe sun formost ofthose days. The mean dailylow
temperature recorded in these nestswas 3.8 ± 0.25°C
40
102gm andthe mean dailyhigh 34.6 ± 1.0°C (12 colony-days,
30-
range = 0-38°C). The mean difference between the
dailyhigh and lowtemperatures in the nests was 30.9
± 0.9°C. The mean daily high ambient temperature
recorded at the study site during this periodwas 16.9
+ 1.5°C. One ofourstudynestswas in amore shaded
118gm
area and experienced direct radiation for onlypart of
the day. For this nest, the mean lowtemperaturewas
3.8 ± 1.0°C andthe meanhigh 17.3 ± 1.0°C (4colony-
days). The mean difference between the daily high
and low temperatures in the nest was 13.5 ± 0.9°C.
For all nests, daily lows occurred in the morningjust
beforedawnanddailvhighsbetween 1200and 1500h.
Daily temperature fluctuation recorded in one nest
overadiree-davperiodis shown in Fig. 3. Ourinvesti-
gations in the study areawere terminated at noon on
26 February"andweobtainedatemperaturerecordfor
the period from 2400 to 0900 h on that day. On the
morning of 26 February, standing water in outdoor
containers had iced over and our data loggers indi-
Timelapse(15minintervals) catedthetemperaturedroppedto-4°Cby0600h, the
Fig. 2. Temperature within the irradiated (solid line) and lowesttemperature recorded duringthe studyperiod.
shaded sides (dotted line) of four empty- nests of T. pityocampa Seasonal and daily activity patterns of field
rinedciocradteeddubnydtehrelhaobroirzaotnotraylcsonhdaidteidonbsa.r.AmAbriroewnstitnedmipceartaetpuorientrsawngheeins colonies. Aseasonaltemperatureprofilecompiledfor
artificialheatsourcewasturnedoff,valuesindicatemassofnests. die studyareafor2000and2001 shows diatthe cater-
164 Journalofthe Lepidopterists' Society
Fig. 4. Monthly mean minimum (gray) and mean maximum
(black) temperatures recorded nearthe studysite overatwoyear
interval.HorizontalbarindicatesapproximateperiodswhenT.pity-
ocampaactivelyforages (gray)andpupatesunderground(white).
pillars feed and grow during the coldest part of the 2400
Time
year and reside as pupa buried in the soil during the
hotsummermonths (Fig. 4). Dailyactivityrecords ob- (verFtiigc.al5.barsB)iamnoddanlesdtaitleymapcetrivaittuyrbeou(tbslaocfkalicnoe)l.onHyoroifzTo.npailtib/aorcianmdpia-
tained during the present study show that during the cates daily photoperiods (white) and scotoperiods (black). Photo-
periodofgrowth, caterpillaractivityoutsidethenestis periodsbeginattheonsetofciviltwilightandendatthetermination
restricted to the coldest part ofthe day (Fig. 5). De- ofciviltwilight.
spite lowearlymorningtemperatures duringthe study
period, colonies were active overnight on all of the notinitiatedforthe mostpartuntilthetemperaturefell
study days. Colonies initiated foraging bouts an aver- below0°C. Caterpillar activitylargelyceasedwhen the
age of93.1 ± 35.2 minutes after the end ofcivil twi- temperature reached -2°C but sporadic activity was
light in the evening (center ofthe sun 6° below hori- recorded at -4°C. When this colony was observed at
zon) andthe lastcontingentofforagers returnedtothe 0900 h on 26 February, allthe caterpillarswerebackin
nest42.9 ± 24.9 minutes before the onset ofcivil twi- the nest. The extent to which the caterpillars fed at
lightinthe morning(N = 26colony-days). Theinterval these sub-zerotemperaturesis notknown.
betweenthe movementofthefirstcontingentofcater-
Discussion
pillars from the nest in the evening and the return of
the last contingent in the morning was 618.0 ± 35.2 Our study, providing the first empirical data set on
minutes. Thus, colonies were typically active on the the temporal foragingpatterns ofcolonies ofthe pine
tree throughoutthe eveningandearlymorninghours. processionary, supports the observation of Fabre
That colonies fed during these overnight forays was (1916) that the caterpillars ofthe pine processionary
evidencedbythepresence offresh leaves in theirguts feed throughout the winter on all but the most frigid
aftertheyreturnedto the nests. In 20 ofthe 26 forag- nights. The pine processionary caterpillar is remark-
ing bouts recorded, colonies moved from the nest to ablein its abilitytolocomote andfeedattemperatures
feeding sites in the earlyevening and returned in the wellbelowthose atwhichthe activityofmostinsectsis
early morning, giving rise to bimodal activitypatterns curtailed. Onlya fewother invertebrates are active at
(Fig. 5). Intheothersixinstances, activitybetweenthe such low temperatures. Some collemboleans (Aitchi-
nest and feeding sites occurred throughout the son 1983), several species ofspiders (Aitchison 1984),
eveningandearlymorning. the cricket Gnjlloblatta campodeifonnis Walker
Colonyactivityonthetwocoldestnightsisillustrated (Prichard & Scholefield 1978), an amphipod (Dunbar
in Fig. 6. Overnight on 17-18 February, colonies were 1957), and acopepod (Kiorboe et al. 1982) have been
continuallyactive even though temperatures measured reportedto moveaboutandfeedattemperatures ator
atnestsites fellto0°Cby2400h. Theambienttemper- slightly below zero. Laboratory studies of the sub-
ature was slightly below freezing at 0900 h when the Antarctic caterpillar Pringleophaga marioni Viette
wholeofcolony1wasobservedtostillbeoutofthenest (Tineidae) showedthatthe larvae are able to maintain
moving about the tree in procession. It is not known motoricfunctions attemperatures aslowas-1.6°Cbut
when the caterpillars returnedto the nest but allwere there are no data to showthat the caterpillars are ac-
backwhenthenestwasnextobservedinlateafternoon. tive at temperatures this lowin their natural environ-
Overnight on 25-26 Februarythe temperature fell be- ment (Klok& Chown 1997).
low 0°C at approximately 2200 h and reached an Locomotion and feeding in caterpillars has been
overnight low of-4°C at 0600 h. Inspection ofthe ac- recorded only rarely at temperatures below5°C (Ke-
tivityrecordforcolony3 (Fig. 6) showsthatactivitywas van etal. 1982,Joos 1992, Kukal 1993, Klok&Chown
Volume 57, Number 3 165
25-, The ability ofthe inhabited nests ofT. pityocampa
2105- 40 towarmwell above ambienttemperaturewhenirradi-
10 20 atedwas demonstratedinlaboratorystudiesbyBreuer
5 and Devkota (1990), but our study shows that even
L- when devoid ofcaterpillars the irradiated nests of T.
-5
2100 pityocampa exhibit large heat gains. The overwinter-
Time ingnests ofthe processionaryare denselypackedwith
silk, frass, andhost materialandthebodies oftherest-
inglarvaearesituatedtightlywithinthem, allowingthe
30 caterpillars to raise theirTb's well above the tempera-
25 -60 ture of the outside air by conducting heat from the
2105 -40 1 structures. Although the relationship between Tb and
10 > the rate ofdigestion has not been determined for the
20
5 processionary, nests situated on host trees to facilitate
the absorption ofsolar radiation achieve thermal max-
-5-
2100 ima during sunlit days that are likelyto be well in ex-
Time cess ofthose required by the caterpillar for efficient
FlG.6. Temperatureinthenest(blackline)andactivityoutside foodprocessingduringmidwinter. Dataavailable fora
thenest(verticaleventbars)oftwocoloniesofT.pityocampa. Hor- fewotherspecies ofcaterpillars that feed at compara-
izontal barindicates photoperiod (white), scotoperiod (black) and
bly lowtemperatures indicate that efficient food pro-
civiltwilight(gray).
cessing by the processionary is likely to require a T
b
that exceeds the winter time air temperatures typical
1997). Anotable exception is the socialcaterpillarEu- ofour study site. The Arctic caterpillar Gynaephora
cheira socialis Westwood (Pieridae) which feeds groenlandica (Wocke) (Lymanthriidae) has an assimi-
throughout the winter in the mountains of Mexico lationefficiencyofonly7% at5°C comparedto40% at
(Fitzgerald & Underwood 2000). The daily tempera- 15°C (Kukal 1993) but the assimilation threshold for
ture profile in the winterin the montane forestwhere Malacosoma americanum (Fabricius) (Lasiocampi-
E. socialis occurs is similarto that ofour studyareain dae),whichis reportedtocollectfoodattemperatures
Cataloniain that the diurnaltemperatures are moder- down to 7°C (Joos 1992), is not reached until the
ate to warm while at night the temperatures plunge caterpillars warm to at least 15°C (Casey et al. 1988).
precipitously and are often near or below freezing. Regardless ofthe thermal demands ofthe procession-
Like T. pityocampa, the caterpillars ofE. socialis feed ary, ourstudyshows thattheirradiatednests ofthein-
only at night and have been recorded outside their sect provide thermally heterogeneous environments
nests at subzero temperatures in midwinter (Fitzger- (Fig. 2) within which the caterpillars might optimize
aldO&urUnstduedrywsohoodws200t0h)a.t the caterpillars of T. pityo- ttuheriers Tdubr'sibngytvhaerydianygtitmhee.irIpnocsointtiroansst,wittehmipnertahteursetrsuci-n
campa locate their nests preferentially in the SE-SW shaded nests will be much cooler and may not allow
quadrant ofhost trees. Brueur et al. (1989) found ap- optimization ofT placing apremium on the correct
proximately 76% and Schwammer and Nemeschkal siting ofthe permab,nent nest bythe third instar cater-
(1987) approximately 80% ofthe nests they surveyed pillars. Although the caterpillars might also achieve
isnamoteheqruaadrreaanst.ofTthhues,Meddaittaerfrraonmeatnhetsoelisetuwdiitehsinshthoiws Tthbe'snceosntdiuncimvidewitontfeoro,dtphreoccoesstswinogulbdybbeasgkrienagteoruetxspiode-
that colonies ofthe processionarylocate theirperma- sure topredators. The mean dailytemperature forthe
nent nests on the side ofthe tree that is likely to re- coldestmonths (November-February) recordedatthe
ceive the most solar radiation. Although fewer nests Font Rubi station from 1999-01 was 10.7 ± 0.7°C and
were found within this quadrant in La Moixeta, this the mean daily maximum temperature for this same
mayhave beenthe casebecause the trees occurred in periodwas 14.7 ± 0.5°C. Thus, ifthe caterpillarswere
youngstands andwere distantlyspacedsothattheyex- to remain hidden outside the nest in protected loca-
paenrdieUnncdeedrlwitotloedsh(a2d00i0n)gffrooumndntehaartbythtereneess.tsFiotfzgEe.raslo-d tlioownesrdtuhrainngthtohseeseamchoinetvhasblteheiinrtThbe'snweosutlddurbiengmutchihs
cialis occurring on open grown and distantly spaced sameperiodandmightbetoolowtoallowtheefficient
madronetreeswereirradiatedbythesunregardlessof
processingoffood.
theirpositioninthe crown ofthe tree. Despitedieabilityofthecaterpillarstowarmwithin
166 Journalofthe Lepidopterists' Society
irradiated nests in midwinter, studies of caterpillars Table 1. Comparison oftraits offive species ofsocial caterpil-
foraging under laboratory conditions (Fitzgerald in lars. Shadedboxhighlights differencesbetweenspecies 1-2which
forageinbothdaylightanddarkness andspecies3-5which forage
press) indicate that under the overall thermal regime only in darkness. 1 = Malacosoma americanum, 2 = Eriogaster
the caterpillars experience in the field they grow at a lanestris, 3 = Gloveria sp.,4 = Thaumetopoeapitijocampaand5 =
rate well below that which they could achieve at sus- Eucheirasocialis. Seetextforreferences.
tained, higher temperatures. Caterpillars maintained
Species
inthelaboratoryat22 + 2°C, underaphotoperiodthat
simulatedthat experiencedbyfieldcolonies ofT. pity- Trait 1
ocampa, exhibited the same nocturnal pattern of ac- 1. Centralplaceforaging y y y y y
tivityas field colonies and did not feed duringthe day 22.. CUonilvoonliteisnaeverage200-300 y y y y y
These colonies, which eclosed from eggs in early Au- siblingsinitially y y y y y
gust, completedtheirlarval development andpupated 3. Coloniesconstructlarge,
by late October, at least 15 weeks sooner than field 4. Lsailrkveaneshhealvteerdsiscrete,coordinated y y y y y
colonies require to complete theirlarval development. boutsofenmassefeeding
Halperin (1990) similiarly found that the social larvae interspersedwithperiodsofrest y y y
5. Larvaeexperiencewarmdays,
oiT.jordana (Stgr.),whichalsofeedduringthewinter, cool/coldnights y y y y y
requiredapproximately 150 days tocompletetheirlar- 6. Caterpillarsdistasteful/urticating y y y y ?
val development in the field but only 48 days when 7. Larvaeformaposematicaggregations
maintained in the laboratory at a constant 25°C. The 8. Noenstthemanyesotvienrhdaeyaltiginhtsunlight y y n n n
likelyreasonforthe difference ingrowth ratebetween causingevacuation y y n n n
field andlaboratorycolonies ofboth ofthese species is 9. Rapid,progressivedeteriorationof
thatwhen maintained at elevated temperatures cater- 10. Lhaorstvaleeagfrqouwalriatpyidly yy yy nn nn nn
pillars are able toboth collect andprocess food during
their nocturnal forays. This allows them to assimilate
more energyeach daythancaterpillarsthatexperience ofE. lanestris commonlyrestontheoutsideofthenest
temperatures too cold to permit food processing dur- and feed away from the structure during the daylight
ingthe overnight foray. In addition, underfield condi- hours, a foraging strategy distinctlydifferent than that
tions, the caterpillars can be expected to assimilate of T. pityopcampa? The answer may be sought in a
little ifanyfoodon cloudywinterdays. suite oftraits that distinguish these two species from
Electronic recordings of daily foraging activity are the three nocturnal foragers (Table 1, traits 7-10). The
now available for five species ofsocial caterpillars. All caterpillarsM. americanum andE. lanestris, bothearly
arecentralplaceforagers sharingovertfeaturesoftheir springfeeders, areunabletofeedonthe agedleavesof
biology (Table 1, traits 1-6). Analysis oftheir activity their host trees. Their need to grow rapidly, in a race
records shows that the caterpillars fall into two distinct against declining food quality, maycompromise safety
groups based on die temporal pattern oftheirforaging forgrowth, favoringcaterpillars drat feedboth dayand
behavior. M. americanum (Fitzgerald 1980, Fitzgerald night. Additionally,thenestsofthesespeciesmayeasily
et al. 1989) and Eriogasterlanestris (L.) (Lasiocampi- overheatonhot andsunnydays forcingthecaterpillars
dae) (Ruf& Fielderin press), feed both dayand night to evacuate the structures and thus compromise their
and grow rapidly, achieving their full larval growth in role as secure retreats (Joos et al. 1988, Ruf& Fiedler
approximately eight weeks. E. socialis (Fitzgerald & 2002). Both species are conspicuous against the white
Underwood 1998a), Gloveria sp. (Lasiocampidae) back ground ofthe nest duringthe day. Both are hairy
(Fitzgerald & Underwood 1998b), and T. pitijocampa and E. lanestris is reported to be urticating (Ruf &
(thisstudy) feedonlyatnight,growslowly, andhaveac- Fiedler in press). Both feed on species of Primus
tivelarvalstageslasting7-9 mondis. Amajorconstraint whose cyanogenic glycosides may offer some defense
oncaterpillars foragingis predationpressure (Stamp & againstpredators when regurgitatedas cyanide (Peter-
Casey 1993) and for all of these caterpillars, defense son 1987, Fitzgerald et al. 2002). Thus, aposematism
against day active predators would best be served by anddistastefulness mayoffsetthe riskofdaytimeexpo-
foraging only at night and by sequestering themselves suretosome extent.
in the nest duringthe day. The eastern tent caterpillar, Moreenigmaticis the factthatthecolonies ofE. so-
for example, has over 200 predators and parasitoids cialis, Gloveria sp., and T. pitijocampa feed onlynoc-
(Fitzgerald 1995), many ofwhich might be avoided if turnally and do not take advantage ofthe warm day-
the caterpillars hid in the nest during the daylight lighthourstocollectadditionalfood. Althoughitisnot
hours. Whythendothe larvaeofthis species andthose known ifE. socialis is distastefultopredators, Gloveria
Volume 57, Number3 \61
sp. and particularlythe older instars ofT. pityocampa Fitzgerald, T. D., T M. Casey& B. Joos. 1989. Dailyforaging
are urtieating (Vega et al. 1999), and it would appear sscohmeadualmeeroifcfaienludmc.olOoencioesloogfitahe76e:a5s7t4e-r5n7t8e.ntcaterpillarMalaco-
that theywouldbe aswell orbetterdefendedthan M. Fitzgerald,T. D., P. M.Jeffers &D. Mantella. 2002. Deple-
americanum or E. lanestris were they to feed in the tionofhostderivedcyanideinthegutoftheeasterntentcater-
daytime. Perhaps mostsignificantisthe factthatthese Fitzpgiellraar,ldM,alT.acDo.so&maD.amL.erAi.caUnnudme.rJw.oCohde.m.19E9c8oal..2T8r:ai2l57m-a2r6k8i.ng
three nocturnally active species feed non-selectively bythelarvaoftheMadronebutterflyEucheirasocialisandthe
on the leaves oftheirhost trees and have no pressing roleofthetrailpheromoneincommunalforagingbehavior.J.
need to accelerate their rates offeeding to keep pace InsectBehav. 11:247-263.
. 1998b. Communalforagingbehaviorandrecruitmentcom-
with a seasonal decline in host quality. Furthermore, munication in Gloveria sp. (Lepidoptera: Lasiocampidae).
J.
the nests ofthese species are denserandmoreopaque Chem.Ecol.24:1381-1396.
to radiation than those of M. americanum and E. . 2000. Winterforagingpatternsandvoluntaryhypothermia
in the social caterpillar Eucheira socialis. Ecol. Entomol.
lanestris and there is no evidence that the whole of 25:1-10
these structures can become uninhabitable due to Halperin, J. 1990. Life history of Thaumetopoea spp. (Lep.,
overheating. They therefore constitute dependable Thaumetopoeidae)inIsrael.J.Appl. Entomol. 110:1-6.
Joos,B. 1992.Adaptationsforlocomotionatlowbodytemperatures
daytime retreats from predators. Thus, as maybe the in easterntentcaterpillars,Malacosomaamericanum. Physiol.
caseforM. americanumandE. lanestris, noneofthese Zool.65:1148-1161.
species needs to compromise safetyforgrowth. Joos,B.,T. M.Casey&T.D.Fitzgerald. 1988. Rolesofthetent
in behavioral thermoregulation of eastern tent caterpillars.
Ecology69:2004-2011.
Acknowledgments Kevan,P. G.,T S.Jensen&J. D. Shorthouse. 1982. Bodytem-
WethankJoanPanadesiGallart,MercePanadesiBias,andRosa peratures and behavioral thermoregulation of high Arctic
MariaGallartiPujolwithoutwhosekindsupportthisprojectwould woolly-bear caterpillars and pupae {Gynaephora rossii, Ly-
nothavebeenpossible. M. Benincore-Posseassistedinthecollec- mantriidae: Lepidoptera)andtheimportanceofsunshine.Arc-
tion of field data. Alfonso Pescador-Rubio provided the Spanish ticandAlpineResearch 14:125-136.
translation oftheabstract. The Catalonia MeterologyServicepro- Kiorboe, T, F. Mohlenberg &H. Nicolajsen. 1982. Ingestion
videdtheseasonaltemperaturedata. rateandgutclearanceintheplanktoniccopepodCentropages
hamatus(Lillijeborg)inrelationtofoodconsumptionandtem-
Literature Cited perature.Ophelia21:181-194.
Aitchison, C.W. 1983. Lowtemperature andpreferredfeeding Kloka,tuCr.eJt.o&lerS.anLc.eCahnodwwna.ter1b99a7l.ancCreiotifcaalsutbh-eArnmtaalrcltiimictsc,atterepmipllearr-,
bywinter-activecollembolans. Pedobiologia25:27-36. Pringleophoramarioni (Lepidoptera:Tineidae). InsectPhys-
. 1984. Lowtemperaturefeedingbywinter-activespiders.J. iol.43:685-694 J.
Arachnol. 12:297-305. Kukal,O. 1993. Bioticandabioticconstraintsonforagingofarctic
Breuer, M. & B. Devkota. 1990. Studies on the importance of caterpillars,pp.509-522.In Stamp,N.E.&Casey,T. M.(eds.),
nesttemperatureofThaumetopoeapityocampa(Den.&Scruff.) Caterpillars: ecological and evolutionaryconstraints on forag-
Breu(eLre,p.M,.T,hBa.umDeetvokpooteai,daEe.).DoJu.mAapp-lP.etEnrtiodmooul,.A1.0K9:o3u3t1s-a3f3t5i.kis& Peteirnsgo.nC,hSa.pCm,anN.aDn.dJHoalhln,sNoenw&YJo.rkL..Leguyader. 1987. Defen-
G. H. Schmidt. 1989. Studyon the exposition andtempera- siveregurgitation ofallelochemicals derived from hostcyano-
ture of nests of Thaumetopoea pitycampa (Den. & Schiff.) genesisbyeasterntentcaterpillars. Ecology68:1268-1272.
Casey(L,epT..,MT.h,auBm.eJtooopso,eiT.daDe.)FinitGzregeecrea.lJd.,ApMp.l.YEunrtolmoonla.&107P:.3Y7o0-u3n7g5.. Pritfceheadridn,gGb.eh&avPi.orS,chaonldefaiseslocdi.at1e9d7s8.ensOebsoerrgvaantsioonfsGornyltlhoeblfaototda,
1988. Groupforaging,thermoregulation,andgrowthofeastern campodeiformis(Grylloblattodea).Can.Entomol. 110:205-212.
tent caterpillars in relation to microclimate. Physiol. Zool. Ruf,C. &K. Fiedler. 2002. Tent-basedthermoregulationinso-
61:372-377. cial caterpillars of Eriogaster lanestris (Lepidoptera: Lasio-
Dajoz, R. 2000. Insects andforests. The role and diversityofin- campidae):behavioralmechanismsandphysicalfeaturesofthe
sectsintheforestenvironment. LavoisierPublishing,Paris. tent. ThermalBiol.27:493-501.
J.
Demolin, G. 1969. Bioecologia de la processionaria del pino, . Inpress. Plasticityinforagingpatterns ofcolonies ofthe
ThaumetopoeapityocampaSchiff.Incidenciadelosfactorescli- small eggar moth, Eriogaster lanestris (Lepidoptera: Lasio-
maticos. Bol. Serv. PlagasForest 12:9-22. campidae).Oecologia.
Dunbar, M.J. 1957. Thedeterminantsofproductioninnorthern Schwammer, H. &H. L. Nemeschkal. 1987. BedeutungderEx-
seas: a study of the biology of Themisto libellula Mandt, position von Raupen-Nestern Pinienprozessionsspinners
"Calanus"Seriesno. 14Can. Zool.35:797-819. (Thaumetopoeapityocampa Schiff.)aufderInsel Krk, Dalmat.
J.
FabreIn,c.J,. NH.ew19Y1o6r.k.Thelifeofthecaterpillar. Dodd, MeadandCo. StampVe,rNh..ED.ts&chT..ZMo.olC.aGseesy..8109:9239.8.Caterpillars:ecologicalandevo-
Fitzgerald,T. D. 1980. An analysis ofdailyforagingpatternsof lutionary constraints on foraging. Chapman and Hall, New
laboratorycoloniesoftheeasterntentcaterpillar,Malacosoma York.
aelmeectrriocniacnaullmy.(CLaenp.idEonptt.er1a1:2:L7a3s1i-o7c3a8mpidae), recorded photo- Vega,LaJ.FMu.e,nIt.eM,onP.eoS,anAc.hAerzme&ntEi.a,SaJ.ncFteirsn.an1d9e9z9.,JA.lVleegragy,tRo.tDhee
. 1995. The tent caterpillars. Cornell University Press, pine processionary caterpillar (Thaumetopoea pityocampa).
Ithaca,NewYork ClinicalandExperimentalAllergy29:1418-1423.
pro.cIensspiroensasr.yTbheeharvoiloerooffaTthraaiulmpehteorpoomeoanpeitiynotchaempfao.raJg.iCnhgeamn.d Zar,CJl.iff1s9,74N.ewBioJsetrasteiys.ticalanalysis. PrenticeHall, Inc. Englewood
Ecol.