Table Of ContentJ.Entomol.Soc.Brit.Columbia91,December, 1994 59
Biological control ofthe two-spotted spider mite in raspberries
with the predator mite,Phytoseiuluspersimilis
L. WOODl,D.A. RAWORTH2,and M. MACKAUERl
^CENTREFORPESTMANAGEMENT,DEPARTMENTOFBIOLOGICALSCIENCES
SIMONERASERUNIVERSITY,BURNABY,B.C.V5A 1S6
2PACIFICAGRICULTURERESEARCHCENTREANDAGRI-FOODCANADA,
6660N.W.MARINEDRIVE,VANCOUVER,B.C.V6T1X2
ABSTRACT
Phytoseiuluspersimiliswas released to control the two-spotted spidermite, Tetranychus ur-
ticae,infieldraspberriesatAgassiz,B.C.Themitepredatorsbecameestablishedandresponded
numericallytotheprey in thetreatmentplots. Foraperiodof8 weeksafterrelease,thenum-
bersofT.urticaewereconsistentlylowerinthetreatmentplotsthaninthecontrols.Differences
innumbersofT. urticaebetweenthetreatmentsandthecontrolsweresignificantontwodates.
Key words: Tetranychus urticae, Phytoseiuluspersimilis, Rubus idaeus, biological control,
FraserValley
INTRODUCTION
The two-spotted spidermite, Tetranychus urticae (Acari: Phytoseiidae) Koch is acommon
A
pestofraspberriesinBritishColumbia. severe infestationcanresultin almostcompletede-
foliationbyAugust. Photosyntheticreservesnecessaryforcoldhardinessarelostifpremature
defoliationoccurs(Jenningsetal. 1964).Aninfestationintheautumncanresultinreducedbud
survivalduring the followingwinter(Doughty etal. 1972). Weakplants leafoutearlierin the
spring,andarethusmore susceptibletolatefroststhanhealthyplants (W.Peters,DistrictHor-
ticulturist,Abbotsford,B.C.,personal communication).
Phytoseiidsarewidelyusedforthebiologicalcontrolofspidermitesonvariousgreenhouse
crops(CostelloandElliott 1981; Morietal 1989;Tanigoshi 1982).Becauseofitshighvorac-
ity, short developmental time, high fecundity (Laing and Huffaker 1969) and good dispersal
ability(McMurtry 1982),PhytoseiuluspersimilisAthias-HenriotisanimportantpredatorofT.
urticaeingreenhouses. Inaddition,P.persimilishasalsobeensuccessfullyusedformitecon-
trol infieldstrawberries inEngland, CaliforniaandNewZealand (Easterbrook 1988; Oatman
etal 1968;Waite 1988).
Wedescribetheresults ofanexperimenttodetermine theefficacy ofP.persimilis as abio-
logicalcontrolagentofT urticaeonraspberrycropsintheLowerFraserValley.
MATERIALS AND METHODS
Theexperimentwas done in aplotofnine rows ofredraspberries,Rubus idaeusL., at the
Agriculture CanadaResearch Station in Agassiz. Eachrow consisted offoureightmetersec-
tionsseparatedbytwometersofbare ground.Threetreatmentsandacontrol wereassignedat
randomwithinarow.Thiswasreplicatedfivetimesonalternaterows,leavingabufferrowbe-
tweentreatments.WereleasedT. urticae,obtainedfromAppliedBionomics(Box2637,Sidney,
B.C. V8L 4C1), on 11 May, 1989 by placing three pieces of mite-infested bush bean leaf
(Phaseolus vulgaris cv Provider) perstool ( a group offive raspberry canes derived from the
sameroot)ontotheraspberryfoliageineachplot.Theprocedurewasrepeatedon9and27July
becausethemitesdidnotbecomeestablishedowingtowet,coldweather.ThepredatorP.per-
similis was introduced on2 August when a sample of30leafletspertreatment indicated den-
sity of0.70 T. urticaeperleaflet. The bean leaveson which thepredators were supplied were
stapledontotheraspberryfoliage inthemiddleofthecanopy innumbersaccordingtothefol-
lowingratiosofadultfemalestopredators: 1:50(High); 1:100(Medium);and 1:200(Low);and
acontrol.
—
r r
•
60 J.Entomol.Soc.Brit.Columbia91 December, 1994
,
60n
(n
c
ZoJ
o
o
0 40-
0)
N
20H
CO
n(D
E
13
—I—
20 40 60
Numbers / leaflet (brushed counts)
Figure1. TherelationshipbetweenestimatednumbersofTetranychusurticaeonraspberryleafletsbydi-
rectcountsandcountsafterremovalwithamite-brushingmachine.
8n 0.12n
B
0)
CO
J? 6H
0.08-
o
n
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C0O
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————— 0.00- ———— —
"I * I ' I ' -| • I ' -|
2 4 6 8 2 4 6 8
Time (wk)
Figure2. PopulationtrendsofTetranychusurticae(A)andPhytoseiuluspersimilis(B)inraspberryplots
at Agassiz, B.C., 1989. Each point is the average offive replicates for the predator/prey treatments:
1:50,(»); 1:100(A); 1:200();andcontrol,(*).Oneaveragestandarderrorofagivenmeandensitywas
1.491 (A)and0.03(B)mitesperleaflet.Timezerowas2AugustwhenP.persimiliswasintroduced.
;
J.Entomol.Soc.Brit.Columbia91,December, 1994 61
Mites were sampledon 13 Augustandatweekly intervals thereafteruntil 1 October. Sam-
plesconsisted of30leafletsperreplicate, 10leafletspickedequally from the top,middle, and
bottom ofthe plant. The mites were removed from the leaves with a mite-brushing machine
(J.G.H.Edwards,LlanfairOrchards,RR1,OkanaganFalls,B.C.),andallstagesotherthaneggs
werecountedat lOXmagnificationunderadissectingmicroscope.
Brushed-mitecountswerecomparedtodirectcountsofmitesonleaves.Twenty-oneleaflets
werepickedatrandomfromraspberryplantsthatwereinfestedwithT.urticae.Themiteswere
countedunderadissectingmicroscope.Eachleafletwasthenpassedthroughthemite-brushing
machine(HendersonandMcBumie 1943),andthe T. urticaewerecountedagain.
The data were analyzed using SAS® REG and GLM Anova procedure with repeated
measures (SAS Institute Inc. 1985). The GLM analyses were performed on log- and square-
root-transformed, and untransformed data with similarresults. The results reported are from
analysesofuntransformeddata.
RESULTSANDDISCUSSION
Theregressionofdirectcounts(y)onbrushed-mitecounts(x)(Fig. 1; =0.732;p<0.01
y = 7.74 -I- 0.82 x) was linear since the addition of x^ to the equation was not significant
(p> 0.05). The x-intercept was not significantly different from zero (p > 0.05). The dataob-
tainedusingthemitebrushingmachinewerethereforeanalyzedwithoutcalibration.
ThepopulationtrendsforT.urticaeinthethreetreatmentsandthecontrolsfollowedasimi-
larpatternduringthefirst2.5 weeksafterrelease,thenthenumbersdiverged(Fig.2A).Over-
alldifferencesbetweentreatments were not significant{p>0.05),butcontrastanalysisusing
Bonferroni'smethodshowed significantdifferencesbetweentheHigh treatmentandthecon-
trolsat4.5weeks{p<0.05),andbetweentheMediumtreatmentandthecontrolat4.5and5.5
weeks(p<0.05).Two-spottedspidermitepopulationlevelsintheHighandMediumtreatments
maintainedthesamepositionrelativetothecontrolsthroughtherestoftheexperimentbutwere
notsignificantlydifferentfromthecontrols(p>0.05).
Phytoseiuluspersimilisbecameestablishedinthetreatmentplotsatlowlevelsandfollowed
apatternofpopulationfluctuationssimilartothatofT. urticae(Fig.2B).AverageP.persimilis
numbersincreasedalmostten-foldwithin3.5weeks.Thenumericalresponsewasanalyzedby
regressingaveragenumbersofP.persimilisonaveragenumbersofT.urticaeforeachtreatment
(High,r2=0.604,p=0.023; Medium,r^=0.608,p=0.023;Low,r^=0.857,p=0.001 and
;
controls,r^=0.309,p=0.153).ThedataindicatethatP.persimiliswasabletofinditspreyand
reproducewhenpreywereabundant.
TheexperimentshowsthatP.persimilis,which isnotnativetoB.C.,canestablishandsur-
viveinaraspberry fieldduringthesummer,foratleast8.5 weeks,atapreydensityof0.7-6.0
T. urticaeperleaflet. SignificanttreatmenteffectsontwodatesindicatethatPpersimilismay
reduceT.urticaenumbersatbotha1:50and 1:100predator/preyratio.Theresultsareinagree-
mentwithotherresearchshowingthat,ingeneral,agentsshouldbereleasedatapredatonprey
ratioofnolessthan l:100(Hoy^ra/. 1982;andMori a/. 1989).
ACKNOWLEDGMENTS
WethanktheAgricultureCanadaResearchStationatAgassizandDr.StanFreemanandDr.
Dave Gillespie for the use oftheir raspberry field plots and laboratory facilities, and Ward
Strong who suggested the project. The principal author, Leslie Wood, thanks herfamily for
supportinghereffortsoveralongperiod.
. .
62 J.Entomol.Soc.Brit.Columbia91,December. 1994
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