Effect of temperature and substrate moisture on group survival of Constrictotermes sp. (Isoptera: Termitidae) under laboratory conditions

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RevistaBrasileiradeEntomologia63(2019)9–11

REVISTA

BRASILEIRA

DE

Entomologia

AJournalonInsectDiversityandEvolution

w w w . r b e n t o m o l o g i a . c o m

Short

Communication

Effect

of

temperature

and

substrate

moisture

on

group

survival

of

Constrictotermes

sp.

(Isoptera:

Termitidae)

under

laboratory

conditions

Dinamarta

V. Ferreira

a,b

_,

_Joseane

_S.

_Cruz

a,b

_,

_Jailton

_J.M.

_Sacramento

a,b

_,

_Marcos

_Leandro

_C.

_Rocha

a,b

_,

Paulo

F. Cristaldo

c

_,

_Ana

_Paula

_A.

_Araújo

a,b,∗

a_Universidade_Federal_de_Sergipe,_Departamento_de_Ecologia,_Laboratório_de_Interaç_ões_Ecológicas,_São_Cristóvão,_SE,_Brazil b_Universidade_Federal_de_Sergipe,_Programa_de_{Pós-Graduaç}_ão_em_Ecologia_e_Conservaç_ão,_São_Cristóvão,_SE,_Brazil

c_Universidade_Federal_Rural_de_Pernambuco,_Departamento_de_Agronomia,_Programa_de_{Pós-Graduac¸}_ão_em_Entomologia,_Recife,_PE,_Brazil

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received23October2018 Accepted28December2018 Availableonline6January2019 AssociateEditor:M.ElianaCancello Keywords:

Bioassays Mortality Termite

a

b

s

t

r

a

c

t

Laboratorybioassaysshouldbeperformedunderappropriateconditionsthatminimizestressand pro-motegreaterlongevitytotestedanimals.Forsocialinsects,forinstance,thestresstriggeredbyremoval individualsfromnestsmayresultinchangesintheirsurvivalandbehavior.Hereweanalyzedtheeffects ofvariationsofdifferentcombinationsoftemperatureandsubstratemoisture(mLofwater/gofnest substrate)ongroupsurvivalofConstrictotermessp.(Termitidae:Nasutitermitinae).Ingeneral,lower substratemoistureresultedinfastermortality.Ontheotherhand,groupssurvivallongerata tempera-tureof26◦Candunderhighersubstratemoisture(2–3mL/7gofnestsubstrate).Theresultofthisstudy maycontributetotheestablishmentofbioassayprotocolsperformedwithConstrictotermessp.inthe laboratory.

Mostofsocialinsectsharbortheircoloniesinneststhatpresent controlledmicroclimate(e.g.temperatureandhumidity), which favorsthemaintenanceofsurvivalandreproductionofindividuals. Differentfromthemostterrestrialanimalsthatexhibitadaptations tominimizethebodywaterloss,termitesaregenerallyvery sus-ceptibletodesiccationduethelowsclerotizationoftheircuticle (NoirotandDarlington,2000).Infact,theseinsectsneed environ-mentalconditionswithhighlevelsofhumidityfortheirsurvival and differentstrategies tocircumventenvironmentalvariations canbeobserved intermites.Termitespeciesthat needtoleave thenest tosearch for foodresources(“central-place foragers”), forexample,buildtunnels/galleriestoprotectthemselvesormay exhibitforaginghabitatthenight(Almeidaetal.,2016).Inspiteof suchstrategies,seasonalvariationsareknowntodirectlyinterfere termiteforagerates(Iqbaletal.,2015;Mouraetal.,2006).

Behavioraland/orecologicalstudiesoftenrequirethecomplete removalofthenestoritspartstoobtainindividualstobeused in laboratorybioassays. However, theremoval of the individu-alsfromtheirnaturalenvironmentmayalreadyinterfereintheir

∗ Correspondingauthor.

E-mail:[email protected](A.P.Araújo).

behavior and survival (Lenz, 2009). Thus, laboratory bioassays shouldbebasedonprotocolsthatallowthemaintenanceof organ-ismsinconditionsascloseaspossibletotheirnaturalenvironment, sothattominimizestressandkeepindividualsaliveaslongasthe testrequires(Carvalhoetal.,2018).Inaddition,themaintenance ofmorefavorableconditionscanalsoavoidbehavioralchanges, whichcouldreﬂectinpatternsinconsistentwiththoseobservedin naturalsituations.

ColoniesofthegenusConstrictotermesarecommonin Brazil-iansavannah(“Cerrado”)andsemi-aridenvironments(“Caatinga”) (Mathews,1977).The individualsof thesespeciesbuildepigeal and/orarborealnestsandtheirforagingoccursatnightthrough columnsintheopenair.Individualsfeedpredominantlyondebris and lichens on the surface of tree barks (Moura et al., 2006; Bourguignon etal., 2011).ColoniesofConstrictotermes spp.can house arange of termitophilesand obligatoryinquiline species (Inquilinitermesspp.) (Mathews, 1977; Cunha etal., 2003; Rosa etal.,2018),andthereforewerestudiedinthelaboratoryinorder toverifythemechanismsinvolvedinthecohabitationoftheirnests (e.g.Cristaldoetal.,2016;Cruzetal.,2018).

In the present study, we perform bioassays to analyze the combinationsoftemperature andsubstratemoisturemost ade-quateforthesurvivalofindividualsofConstrictotermessp.under https://doi.org/10.1016/j.rbe.2018.12.004

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10 D.V.Ferreiraetal./RevistaBrasileiradeEntomologia63(2019)9–11 24°C 26°C 27°C 25°C 10000 10000 10000 10000

Mean time to death (min)

8000 8000 8000 8000 6000 6000 6000 6000 4000 4000 4000 4000 2000 2000 2000 2000 a 0 0 0 0 0 0 0.5 1.0 1.5

Substrate moisture Substrate moisture 2.0 2.5 3.0 0.5 1.0 1.5 2.0 2.5 3.0 0.5 1.0 1.5 2.0 2.5 3.0 a a b b b c a a a b b _b c a a b b b b b a a b b c c c 0 0 0.5 1.0 1.5 2.0 2.5 3.0

Fig.1.SurvivalofConstrictotermessp.indifferentcombinationsoftemperatureandsubstratemoisture(mLofwater/7gofnestsubstrate).Differentlettersineachgraphic meansigniﬁcantdifferenceamongtreatmentsofhumidity.

laboratoryconditions.Thestudywascarriedoutusingsixnests thatweretotallyremovedfromtheﬁeld,in themunicipalityof SãoCristóvão(1101◦S, 3712◦W), Sergipe,Brazil.The bioassays wereconductedinPetridishes(5.5×1.5cm)coveredwith7gof thesubstratefromthecentralpartofthenests(i.e.darkpartwith highcontent of organic matter), that was previously sieved in mesh(6mm).Twentyindividuals(16workersand4soldiers)were placedunderthesubstrateofeach Petridish.During bioassays, nofoodwasofferedtotheindividuals.Thetreatmentsconsisted ofdifferentcombinationsoftemperature (24,25,26 and27◦C) andsubstrate moisture(0.0,0.5,1.0, 1.5,2.0, 2.5 and3.0mLof distilledwater/7g ofnest substrate)determinedby a complete factorial.Thelevelsofsubstratemoisturewereestablishedwith theadditionof differentvolumesof water in a pieceof cotton placed in the center of each Petri dish. The temperature was regulated in biochemical oxygen incubator (BOD), kept in the absenceoflight.Foreachcombinationoftreatments(n=28)three repetition/nest(n=6)wereperformed,totaling504Petridishes. The observations consisted in quantifying thenumber of dead individualsovertime.Dataweresubmittedtocensoredsurvival analysisunderWeibulldistribution,inRsoftware(RDevelopment CoreTeam,2016).Foreachtreatment,themeantimetodeathof individualsfromeachnestwascalculated.Then,thesedata(mean time todeath –“y axis”) weresubmitted toDeviance Analysis (ANODEV)todeterminetheeffectofcombinationsoftemperature xsubstratemoisture(“xaxis”)onsurvivalofConstrictotermessp.

Our results showed that the mean time to death was signiﬁcantly affected by temperature and substrate moisture (F9,154=26.85, p<0.001) (Fig. 1). In general, the conditions of

lower substrate moisture(0.0–0.5mLof water/7gof nest sub-strate) resulted in faster mortality (885.83±16.77min). These resultscorroborate withother studies that showedthe impor-tanceofmaintaininghighhumidityfortermitesurvival(Gautam

andHenderson,2011;Wiltz,2012;ZukowskiandSu,2017).Here, weobservedthatforConstrictotermessp.,thetemperatureof26◦C combined withhigher substrate moisture (2–3mLof water/7g ofnestsubstrate)weretheconditionsthatallowedgreater sur-vivaloftheindividualsinthelaboratory(8525.81±136.84min[e.g. 5.92±0.10days]).Inadditiontointerferinginthesurvivalof indi-vidualsasobservedhere,otherstudieshavealreadydemonstrated that variations in environmental conditions may also change termite behavior, such as tunneling patterns (Arab and Costa-Leonardo,2005),feeding(Sheltonetal.,2011)andintercolonial aggressiveness(CorneliusandOsbrink,2009).

Inconclusion,herewehighlighttheimportanceofmaintaining adequateconditionsforthesurvivalofConstrictotermessp.under laboratoryconditions.Theresultofthisstudymaycontributeto theestablishmentoflaboratorybioassayprotocols.

Contributors

PFCandAPAAconceivedtheresearch.DVF,JSC,JJMSandMLCR collectedthecolonies intheﬁeld andperformedthebioassays. APAAperformedthestatisticalanalyses.DVF,PFCandAPAAwrote the manuscript. All authors approved the ﬁnal version of this manuscript.

Conﬂictsofinterest

Theauthorsdeclarenoconﬂictsofinterest.

Acknowledgments

We thanktheUniversidadeFederaldeSergipefor providing logisticsupport.ThisstudywaspartiallysupportedbyCNPqand CAPES.

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