Reproduction and longevity of the predatory mite, Phytoseiulus persimilis (Acari: Phytoseiidae) and its prey, Tetranychus urticae (Acari: Tetranychidae) on different host plants

6 Pages·1994·3.4 MB·English

by  David R Gillespie

J.Entomol.Soc.Brit.Columbia91.December, 1994 3
Reproduction and longevity ofthe predatory mite,Phytoseiulus
persimilis (Acari: Phytoseiidae) and its prey, Tetranychus
urticae (Acari: Tetranychidae) on different host plants*
DAVID R. GILLESPIE and D.J.M. QUIRING
PACIFICAGRICULTURERESEARCHCENTRE,AGRICULTUREANDAGRIFOODCANADA,
P.O.BOX1000,AGASSIZ,B.C.VOM1AO
ABSTRACT
The biological control oftwospotted spidermites by the predatorPhytoseiuluspersimilis is
usuallyunsuccessfulongreenhousetomatocropsinBritishColumbia.Experimentswerecon-
ductedtodeterminetheinfluenceofhostplantonthelongevityandreproductionofthepreda-
tor, andonthe suitability oftwospotted spidermites asprey. Lifespan andreproductionofP.
persimiliswerelowerontomatoleavesthanonbeanleavesbutfeedingonspidermitesthathad
beenrearedon tomatoorbean leaves hadnoeffecton the reproductionorlifespan ofP.per-
similis.Astrainoftwospottedspidermitesthatcamefromanoutbreakonagreenhousetomato
croplivedforshorterperiodsandlaidfewereggswhenconfinedontomatoleavesthanonbean
leaves.Astrainoftwospottedspidermitesthathadbeenmaintainedonbeanleaveswasunable
toreproduceontomatoleaves.ExudatesfromglandularhairsweretoxictoP.persimilis.Glan-
dularhairsareimportantinpestmanagementontomatocrops.Theirremovalthroughbreeding
mightmakeplantsmoresusceptibletoherbivores.Thereforeitwouldbepreferabletodevelop
othermethodsforbiologicalcontroloftwospottedspidermitesontomato.
INTRODUCTION
Biologicalcontroloftwospottedspidermites,TetranychusurticaeKoch(Acari: Tetranychi-
dae)byPhytoseiuluspersimilis(DosseandBravenboer(Acari: Phytoseiidae) is successful on
wide range ofgreenhouse crops throughout the world (vanLenteren and Woets 1988). How-
ever,theuseofthispredatorforbiologicalcontrolofT. urticaeongreenhousetomatocropshas
beenunsuccessfulinBritishColumbia,andelsewhere(Ravensburgetal 1982).Thishasbeen
attributedtotheentrapmentofP.persimilisontheglandularhairsonthestemsandleafpetioles
oftomatoplants(vanHarenetal. 1987).
Itispossiblethatotherfactorsassociatedwithhairinessmay alsobe involved inthelackof
efficacyofP.persimilisongreenhousetomatocrops.Manymechanismsofresistancetoinsects
andmiteshavebeenidentifiedintomato(FarrarandKennedy 1991b).Severaltoxicandrepel-
lantchemicals,forexample 2-tridecanone,arepresentinthe glandularhairsandontheleaves
oftomato plants (Farrarand Kennedy 1991b). A predator such as P. persimilis would be ex-
posedtothesechemicalseitherdirectly,throughcontactwiththeleaf,orindirectly,throughin-
gestionofprey.
Manyofthemechanismsofresistance intomatoareeffective against T. urticae(Farrarand
Kennedy 1991b). The degree to which the tomato plant affects reproduction and population
growthinspidermitepopulationsmightaidindeterminingstrategiesfordealingwiththispest.
Wepresenthereresultsofexperimentstodeterminethemortalityandfecundityofthepreda-
torymite,P.persimilisanditsprey,T. urticae,ontomatoleaves.
MATERIALS AND METHODS
General:Thespidermitestrainsusedinthisstudyweremaintainedincontinuouscultureon
theirrespectivehostplants. The strainadaptedtofeedingonbean (B-strain) originatedfrom a
commercial insectary (Applied Bio-nomicsLtd., Sidney, B.C.) where ithad beenreared con-
tinuouslyonsnapbean{PhaseolusvulgarisL.)forseveralyears.Thestrainadaptedtofeeding
on tomato {Lycopersicon esculentum Mill.) (T-strain) originated from an outbreak on tomato
plantsinagreenhouseinSurrey,B.C. in 1992.
TheB-strainmiteswererearedonpintobeans(P. vulgaris)inpotsonalaboratorybench.The
4 J.Entomol.Soc.Brit.Columbia91,December, 1994
plants were inoculated weekly from stock materials obtained from Applied Bio-nomicsLtd.
TheT-strainmiteswererearedonexcisedtomatoleaflets(cvDombito,DeRuiterSeeds,Ohio)
onstyrofoamtraysfloatinginwaterfilledtrays.Thepetiolesoftheleafletswereinsertedthrough
holes inthestyrofoamintothewaterbelow.Freshleaveswereaddedtothetraysasrequired.
The P. persimilis used in these experiments were also obtained from Applied Bio-nomics.
Eggs ofP.persimilis were produced forexperiments by isolating 2 to 5 females ondetached
beanleavesonwater-saturatedcottonbattingandprovidingthemwithabundantspidermites.
The predatoreggs were removed every 24h. Females ofP.persimilis were produced forex-
perimentsbyrearingsingleeggstoadultsondetachedbeanleaveswithanabundantsupplyof
spidermites (B-strain). The predators wereexamined daily, and the females were used inex-
periments within 24h ofthe final molt to adult. All experiments were conducted in growth
chambersat26''Cunder 16hoflightfromcoolwhitefluorescenttubes.
Twospotted spider mites: The effects ofhost plant species and spidermite strain on egg
hatch,development,andsurvivaltoadultofT. urticaeweredeterminedonleafdiscsonwater-
saturatedcottoninpetridishes.Eightdiscs, 1 cmindiam.,ofeachplantspecieswereplacedin
rowsoffouronwater-saturatedcottonbattingineachoften,9.2cmsquare,plasticPetriplates.
A single spidermite egg (< 24h old) was placed oneach leafdisc. Fourbean leafdiscs in
each platereceived B-strainmite eggs,andfourreceivedT-strainmiteeggs. Fourtomatoleaf
discs received T-strain mite eggs and fourreceived B-strain eggs. The spidermites were ob-
serveddaily throughtheirdevelopment. Molts weredeterminedbythepresenceofcast skins.
Spidermitesweremovedtofreshleafdiscsasrequired.
Theeffectsoftheplanthostonreproductioninthetwostrainsofspidermiteweredetermined
in an identical experimental design to that above, except that adult females (<24h old) were
placedonleafdiscs.Thesefemaleswereobtainedbyrearingspidermitesindividuallyontheir
respectivehostplantsfromtheprotonymphstage.Femalesatthequiescentdeutonymphstage
wereconfined withmales.Onmoltingtoadult,boththe femaleandthemale were transferred
toeitherbeanortomatoleafdiscsintheexperiment.Eggswerecountedandremoveddaily.The
mitesweretransferredtofreshleafdiscsasrequired.Resultswereanalyzedasafactorialdesign
byanalysisofvariance(ProcGLM,SAS Institute 1992).
Predatormites:TodetermineifplantspeciesaffectedreproductionofP.persimilis,asingle
female(<24hold)wasplacedwithamaleoneitherabeanleafdiscinfestedwithB-strainspi-
dermitesoronatomatoleafdiscinfestedwithT-strainspidermites.Predatoreggswerecounted
daily.Predatorsweretransferredtofreshleafdiscsasrequired.TheresultswereanalyzedbyT-
test.
Developmenttime ofP.persimilisfedonthe twodifferent strains wasdeterminedon2cm
diam. plastic discs floating on water-saturated cotton batting in aPetri dish. Fourdiscs were
placedineachPetridishandasingleeggofP.persimiliswasplacedoneachdisc.Aftertheeggs
hatched,twoofthepredatorswerefedeggsofspidermitesrearedonbeanplants,andtwowere
fedeggsofspidermitesrearedontomatoplants.Eggswerecollectedwith acamel-hairbrush
fromactivespidermitecolonies.Anexcesssupplyofeggswasplacedoneachdisc.Moltswere
determinedbythepresenceofcastskin.TheresultswereanalyzedbyT-test.
Todetermine iftheeffectsseeninthepreviousexperimentwereduetoplantspeciesorspi-
dermitestrain,adultfemaleP.persimilis(<24hold)wereplacedonstyrofoamdiscs2.5cmin
diam. Mixed age populationsofspidermites were provideddaily onfreshpiecesofleaf. The
prey wereeitherB-strainspidermitesonabeanleaf, B-strainmitesonatomatoleaf,T-strain
mitesonatomatoleaf,orT-strainmitesonabeanleaf.Predatoreggswerecountedandremoved
daily. Onlyrecordsforthosefemalesthatdiedofnaturalcausesonthedisc surfacewereused
foranalysis.Mitesthatabandonedthediscsanddrownedwerenotincludedintheanalysis.Re-
sultswereanalyzedbyafactorialdesignanalysisofvariance(ProcGLM,SASInstitute, 1992).
Thetoxicity ofexudatesfrom glandularhairsoftomatotoP.persimilisfemales wasdeter-
minedbyexposingthemdirectlytoglandularhairs,ortoanaqueoussolutionofexudates,orto
water. Twenty miteswere exposed directly to glandularhairs. These wereheld onthe tipofa
moistcamel-hairbrushandlightlytouchedto30to40glandularhairsonapieceoftomatostem.
They werethenplacedonasheetoffilterpapertorecover,thenheldforexamination. Twenty
J.Entomol.Soc.Brit.Columbia91,December, 1994 5
mites,selectedatrandom,wereexposedtoexudatesolution.Theseweredippedfor4secinthe
solution,placedonfilterpapertodry,andthenheldforexamination.Thesolutionwasprepared
bycollectingexudate fromthetipsofglandularhairs,allowingthistodry overnight, thendis-
solving0.28gofthedriedexudatein2mlofdistilled,de-ionizedwater.Twentymitesweresim-
ilarly dipped in distilled, de-ionized water. After 24h, the dead mites were counted. Results
wereanalyzedbyax^testforgoodnessoffit.
RESULTS
Twospottedspidermites:Neitherhostplantnormitestrainhadasignificanteffect(p>0.05)
on the proportion ofeggs hatching (Table 1). There was a significant interaction (F=18.11,
/7>0.001) between host plant and mite strain with respect to survival ofmites from hatch to
adult. There washighmortality ofB-strain spidermites on tomatoleafdiscs,butnotonbean
leafdiscs,andlowmortalityoftomatostrainspidermitesonbothtomatoandbean.Duetohigh
mortalityofB-strainmitesontomatoleafdiscsdataondevelopmentofthisstrainwerenotin-
cluded in the analysis. Instead, host plant/mite-strain combinations were used as three treat-
mentsinatwo-wayanalysisofvariancewithsexofthemiteastheothermaineffect.Therewas
no interaction between sex ofmite and treatment (p>0.05). Neither sex ofthe egg nor host-
plant/mite-straincombinationhadaneffectonthetimetoegghatch(p>0.05;Table2).Female
mites tooklongertodevelopfrom larvae toadultsthan males (F=4.71,p=0.0331). Treatment
Table1
Meannumberofeggshatched, andsurvival toadult in 10cohortsof4mitesofeach strainonbeanand
tomatoleafdiscs.
Hostplant Mitestrain Numberhatchedoffour(N=10) Proportionsurvivingoffour(N=10)
Bean Bean 3.6 0.90
Tomato 3.7 0.85
Tomato Bean 3A 0.03
Tomato 3.5 0.88
MeanSquareError 0.3167 0.1721
AnovaResults
Hostplant F(p) 1.26(0.2685) 15.42(0.0004)
Mitestrain Fip) 0.32(0.5776) 13.37(0.0008)
HostXStrain F(p) 0.00(1.000) 18.11 (0.0001)
Table2
Mean(N,StandardError)numberofdaysfortomatoandbeanstrain spidermitestocompletedevelop-
mentontomatoandbeanleafdiscs.
Hostplant Mitestrain Male Female
Egg Total* Egg Total*
Tomato Tomato 5.3a 10.0a 5.0a 11.2a
(7,0.18) (7,0.90) (19,0) (19,0.46)
Bean Tomato 5.2a 5.2b 5.3a 5.7b
(9,0.15) (9,0.36) (18,0.11) (18,0.27)
Bean Bean 5.1a 5.1b 5.2a 5.6b
(19,0.11) (19,0.19) (10,0.20) (10,0.16)
*Timefromegghatchtomolttoadult
Meansinacolumnfollowedbythesameletterarenotsignificantlydifferent.
5
6 J.Entomol.Soc.Brit.Columbia91,December, 1994
Tables
Egg production and survival ofbean strain and tomato strain adult female twospotted spidermites on
beanandtomatoleafdiscs.
Hostplant Mitestrain N NumberofEggs DaysAlive
Bean Bean 9 49.7 13.2
Tomato 1 38.7 16.6
Tomato Bean 10 0.6 6.0
Tomato 8 2.6 10.0
MeanSquareError 27.8203 7.4501
AnovaResults
Hostplant F(p) 22.75(0.0001) 8.55(0.0058)
Mitestrain F(p) 0.26(0.6124) 2.43(0.1270)
HostXstrain F(p) 0.55(0.4637) 0.02(0.8960)
Table4
Meandevelopmentandreproductionparameters(±standarderror)forPhytoseiuluspersimilisfeedingon
spidermitesonbeanortomatoleaves(N= 10).
Hostplant: Bean Tomato
DevelopmentTime 2.6±0.18 2.810.17
TotalEggsLaid 56.015.67 38.113.34*
DaysofOviposition 13.9±1.50 9.610.87*
Lifespan 20.712.71 11.310.60*
Eggslaidperday 3.010.46 3.410.28
*Significanteffectofhostplant(T-test,p<0.05)
(host-plant/mite-straincombination)hadasignificanteffectonthetimefordevelopmentfrom
eggtoadult(F=134.96;/7<0.0001).BothmaleandfemaleT-strainmitesrequiredsignificantly
longertodevelopontomatothaneitherT-strainmitesonbeanorB-strainmitesonbean.
Spidermitesproduced significantlyfewereggsonleafdiscsoftomatothantheydidonleaf
discsofbean(Table3).Spidermitelifespanwasalsoshorteronleafdiscsoftomatothanonleaf
discsofbean. Strainhadnoeffectoneithereggproductionorlongevityofspidermites.
Predatormites: Therewasnoeffectofspidermite (prey) strainondevelopmenttimeofP.
persimilisonleafdiscs(Table4).Femalesondiscsoftomatoleaflaidfewereggsoverashorter
periodandhadshorterlivesthanfemalesondiscsofbeanleaf(Table4).Therewasnoeffectof
hostplantspeciesontherateofoviposition.
WhenP.persimiliswereconfinedonstyrofoamdiscsandsuppliedwithpreyonleafpieces,
therewasnoeffectofhostplantleafpiecesonthelifespanorfecundityoffemaleP.persimilis
(Table5).FemalesthatwerefedB-strainmiteslivedforasignificantlyshortertimethanfemales
thatwerefedT-strainmitesirrespectiveoftheplantspeciesonwhichthespidermiteswerepre-
sented.
TenpercentoffemalesofP.persimilisdiedafterexposuretowater,50%diedafterexposure
toasolutionaglandularhairexudates, and 85%diedafterdirectcontactwithglandularhairs.
Theseweresignificantdifferences(X'^=22.6,/?<0.05).
DISCUSSION
Thetwospottedspidermite, T. urticae,isbroadlypolyphagous.However, somespidermite
populations are selectively adapted toonly some ofthe plants thatare partoftheirhostrange
(Fry 1989). Itisprobablethatnospidermitepopulationisabletofeedandreproduceonallof
J.Entomol.Soc.Brit.Columbia91,December, 1994 7
theknownhosts.TheT-strainofspidermitesusedinthisstudyoriginatedfromanoutbreakon
atomatocrop inacommercial greenhouse. However, itwasable tousebean,P. vulgaris, asa
host, andsurvivedandreproducedbetteronbeanthanontomato(Table 3). Therewerenodif-
ferencesinreproductionorsurvivalbetweentheB- strainandtheT-strainonbean.Ontomato,
theB-strainofT. urticaewasvirtuallyunabletoreproduce.Veryfewimmaturessurvivedtore-
produce,andfemalesplacedontomatolaidfeweggs.
ThereproductiveabilitiesoftheT-strainofT.urticaearesoreducedontomatothatitappeared
surprisingthatthisstrainwasabletosurviveontomato,letalonegenerateanoutbreak.However,
inlaboratoryculturethis strainreproducedrapidlyonexcisedleavesoftomato. Themajordif-
ferencebetweenthelaboratorycultureandtheexperimentsdescribedherewasthatmanyspider
miteswereusedtostartaculture,whereasasinglemitewasusedinexperiments.Thelargenum-
berofmitesusedtoinoculatethelaboratorycolonyproducedcopioussilk.Mitestendtowalkon
the silk and would therefore have been isolated from the leafsurface. Tomato plant glandular
hairs contain many substances that are toxic to twospotted spidermites (Farrar and Kennedy
1991b).Thesilkwouldtendtoprotectthemitesfromtheeffectsofthehairsandthelargernum-
berofmitesontheleafwouldtendtodiluteexposuretoglandularhairsubstances.
Thestrainofspidermitehadnoeffectonthefecundityofthepredator,P.persimilis.Inanini-
tialexperiment(Table 4) fecundity was lowerforfemales feeding onT-strain spidermites on
tomato leaves than for those feeding on B-strain spider mites on bean leaves. On styrofoam
discs,neitherthe strainofspidermites northeplantspeciesonwhichthey wereprovidedhad
anysignificanteffectonreproductioninthepredator.Thisisprobablybecausethepredatorsdid
nothave to spendall oftheirtime ontheplant section provided,butcould move aboutonthe
styrofoamdisc,thusavoidingcontactwiththeglandularhairs.
PredatorsthatwerefedonB-strainspidermiteshadshorterlivesthanpredatorsfedontheT-
strainmites(Table5). Intheseresultstheinteractionbetweenhostplantandspidermite strain
was notsignificant. However, itislargeenough to indicate thatthe significanteffectofspider
mite strainon lifespancouldhave resulted from the shortlifespan (15.3 days) ofP.persimilis
thatwerefedB-strainspidermites ontomatoleafpieces.LifespanofP.persimilis in all other
treatments was greaterthan 18 days. Mortality among B-strain mites on tomato leaves could
have reduced the number of prey available to P. persimilis. Plant resistance characters are
known to affect the biology ofnatural enemies, even though Wheatley and Boethel (1992)
showedthatresistancetospidermitesinsoybeans{Glycinemax)hadnoeffectonP.persimilis.
However, other natural enemy associations are affected by resistance characteristics in soy-
beans(OrrandBoethel 1986,RogersandSullivan 1986,YanesandBoethel 1983).Resistance
to Manduca spp. (Lepidoptera: Sphingidae) in tomato has toxic effects on the parasitoid Te-
lenomussphingis(Hymenoptera: Scelionidae) (FarrarandKennedy 1991a).
Tables
NumbersofeggslaidandlifespanforPhytoseiuluspersimilisfemalesheldonstyrofoamfloatingdiscsand
fedspidermitesrearedoneitherbeanortomatoleaves(N= 10).
Hostplant Mitestrain TotalEggs Lifespan(days) Eggsperday
Bean Bean 53.1 18.1 3.2
Tomato 54.9 18.9 3.1
Tomato Bean ) 44.2 15.3 3.0
Tomato 42.6 19.9 2.4
MeanSquareError 23.95 3.9 1.53
AnovaResults
HostPlant F(p) 1.96(0.1701) 0.51 (0.4801) 0.98(0.3283)
MiteStrain F(p) 0.00( .9895) 4.58(0.0392) 0.53(0.4714)
HostXStrain F(p) 0.05(0.8236) 2.27(0.1407) 0.37(0.5475)
8 J.Entomol.Soc.Brit.Columbia91,December, 1994
ThehostplantofthespidermiteuponwhichP.persimilisfeddidnotgreatlyaffectthebiol-
ogyofthepredator.FemalesofP.persimilisconfinedontomatoleafletshaveashorterlifespan
thanfemalesconfined onbeanleaves. As aconsequence, the numberofeggslaid isreduced,
andpopulationgrowthandpredationwouldbereduced.Thiseffectisduetocontactwithleaf,
nottheconsumptionofprey.EatingB-strainmitesfedontomatoreducedthelifespanofP.per-
similis.Thecauseofthiswasnotclear.
Upto75% ofP. persimilis die moving from leaftoleafon tomatoplants (vanHarenetal.
1987). Ifthereproductionoftheremainderisreducedbyupto40% asaresultofreducedlife-
spanonleafblades,thenitwouldappearthatenormousnumbersofpredatorswouldhavetobe
introducedintotomatocropstooffsettheseeffects
Resistanceintomatoplantstospidermitescanbeaffectedtosomedegreebyenvironmental
factors.Increasedfertilizationreducesresistancethroughloweringbothglandularhairdensities
and2-tridecanonelevels (Barbouretal. 1991). Glandularhairdensity isconversely increased
inlong-day,highlightlevelconditions(Kennedyetal. 1981).Glandularhairdensityandother
resistance factors mightbe reduced through breeding. However, resistance to pestsbased on
glandularhairs is importantforpreventingfeedingbymany speciesofherbivores(Farrarand
Kennedy 1991b),andshouldnotbediscardedforthesakeofsinglepredator/prey association.
ItwouldbepreferabletodevelopalternativestrategiesforreleasingandmanagingP.persimilis
intomatocrops,ortoseekotherpredatorspeciesthatarenotaffectedbytheresistancemecha-
nismsoftomato.
ACKNOWLEDGEMENTS
WethankJ.Treumeitfortechnicalassistanceonpartsoftheproject,andAppliedBio-nomics
Ltd.,Sidney,B.C.,Canadaforthesupplyofspidermitesandpredators.
NOTE
1. Contributionnumber516fromthePacificAgricultureResearchCentre,Agassiz,B.C.
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