Occurrence of the Western Flower Thrips, Frankliniella occidentalis , and potential predators on host plants in near-orchard habitats of Washington and Oregon (Thysanoptera: Thripidae)

2011·9.5 MB·English

by  Eugene Miliczky

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J.Entomol.Soc.Brit.Columbia108,December201 11
Occurrence ofthe Western Flower Thrips, Frankliniella
occidentalism and potential predators on host plants in near-
orchard habitats ofWashington and Oregon (Thysanoptera:
Thripidae)
EUGENE MILICZKYi 2, and DAVID R. HORTONi
ABSTRACT
One hundred thirty species of native and introduced plants growing in uncultivated land
adjacent to apple andpearorchards ofcentral Washington andnorthern Oregon were sampled
for the presence of the western flower thrips (WFT) Frankliniella occidentalis (Pergande,
1895) andpotential thripspredators. Plantswere sampledprimarilywhile in flower. Flowering
hosts for WFT were available from late-March to late-October. Adult WFT occurred on 11
plant species and presumed WFT larvae were present on 108 of 119 species. Maximum
observed WFT density on several plant species exceeded 100 individuals (adults and larvae)
per gram dry weight of plant material. The most abundant predator was Orius tristicolor
(White, 1879) (Heteroptera: Anthocoridae). It was collected on 64 plant species, all ofwhich
were hosts for WFT. The second most abundant predators were spiders (Araneae). Small
spider immatures (first and second instars) of several species were common on certain host
plants, andare likelyto feedonWFT.
Key Words: Frankliniella occidentalis, western flower thrips, host plants, predators, Orius
tristicolor,Araneae, spiders.
^INTRODUCTION
The western flower thrips (WFT) especially honeybees. Apis mellifera
Frankliniella occidentalis (Pergande, 1895), Linnaeus, 1758, are active in the orchard
was originally distributed throughout western canopy. It has also been difficult to determine
North America (Kirk and Terry 2003). In the when, during fruit formation, damage-causing
past 30 years WFT has spread to much ofthe oviposition occurs and, consequently, when
rest of North America and now also occurs control measures are most needed (Cockfield
throughout Europe and parts of North Africa etal 2007).
(Kirk and Terry 2003). It is a pest in both the Host plant utilization by WFT is very
field and the greenhouse, attacks a large broad. Bryan and Smith (1956) found it on
number of crops, and causes damage by 139 plant species (representing 45 families) in
feeding, oviposition, and most importantly, California, which is within the pest's original
transmission of Tospoviruses (Reitz 2009). geographic range. In areas to which it has
WFT
is an important secondary pest ofcertain spread, hostplant utilization is also broad, and
apple varieties in the Pacific Northwest, in Hawaii it was found on 48 plant species on
producing a pale, cosmetic blemish known as the island of Maui (Yudin et al. 1986).
a pansy spot that forms around the site of Chellemi et al (1994) found it on 24 of 37
oviposition (Venables 1925; Madsen and Jack plant species surveyed in Florida within a
1966). Although the damage is superficial, decade after its first detection. In a study done
affected fruit may be downgraded at harvest barely ten years after the insect was first
(Madsen and Jack 1966; Terry 1991). Control reported all 49 plant species sampled in
ofWFT on apple can be challenging because Turkey harbored WFT (Atakan and Uygur
it occurs on trees primarily when pollinators, 2005). In Chile, where it has become a serious
' Yakima Agricultural Research Laboratory, United States Department of Agriculture - Agricultural Research
Service,5230KonnowacPassRoad,Wapato,WA98951
2Correspondingauthor: gene.miliczky@,ars,usda.goy
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12 J.Entomol.Soc.Brit.Columbia108,December201
agricultural pest, WFT occurred on 50 of 55 a number of these host plants, apparently in
plant species and appears to have supplanted a associationwithWFT.
native species of Frankliniella as the most In this study, we surveyed native and
common thrips species (Ripa etal. 2009). introduced plant species in fruit-growing
Anumber ofpredators are known to attack regions of central Washington and northern
WFT (Sabelis and Van Rijn 1997). Few ofthe Oregon where WFT is a secondary pest of
studies that have reported on WFT's certain apple varieties. Our objectives were to
WFT
occurrence on non-crop plant species have 1) gain an understanding of utilization of
also reported on the presence of predator non-cultivated host plants typical of near-
species. Northfield et al. (2008) studied the orchard habitats in the study areas, 2) develop
population dynamics of WFT on seven a better understanding of WFT phenology
uncultivated host plants and also reported on across the season, and 3) improve our
the occurrence ofthe important thrips predator understanding of known and potential WFT
Orius insidiosus (Say, 1832) (Heteroptera: predators occurring on these non-cultivated
Anthocoridae). Tommasini (2004) monitored host plants, with emphasis on minute pirate
Orius populations on known host plants of bugs (Heteroptera: Anthocoridae) and spiders
WFT in Italy and found that several species of (Araneae).
Orius commonly occurred at high densities on
MATERIALS AND METHODS
Study Sites. This study was conducted at consisted of mixed hardwood/coniferous
11 sites in Washington State and two sites in woodland. Trees included Pinus ponderosa
northern Oregon (Table 1). Virtually all Dougl. (Pinaceae), Pseudotsuga menziesii
sampling was done in native habitat (Mirbel) Franco (Pinaceae), Acer
immediately adjacent to orchards, generally macrophyllum Pursh (Aceraceae), and
within 100 m ofan orchard edge; a few plant Quercus garryana Dougl. (Fagaceae).
species of interest that occurred in the Understories at all three sites consisted of a
understory of orchards were also sampled. variety ofshrubs and forbs.
Most of the sites were in Yakima County, Sampling for tiirips and predators. The
Washington, located in the south-central part Yakima County study sites were visited at
of the state. Two sites were near Hood River approximately weekly intervals during 2002
innorthern Oregon(Table 1). from early April to late October. Due to
With one exception, each tract of native greater travel distances the Grant County site
habitat was at least several hectares in area was visited bi-weekly, and the Chelan County
and adjacent to orchard habitat. The only and Oregon sites were visited monthly from
m
exception was a tract comprising a 25 wide April to July. Sampling in 2003 was limited to
strip of native vegetation occurring between selected plant species (see below) at sites in
an orchard and an irrigation canal. Native Yakima County. Durey and Hambleton were
habitat at all Yakima County and the Grant visited weekly from late March to late
County locales was sagebrush steppe (Table October, while the other Yakima County sites
1). Sagebrush steppe at Hambleton, Durey, were visited when species ofinterest were in
and Sunset fell within the lithosol zone of flower. During each visit, observations were
Taylor (1992), and is characterized by thin, made of plants in flower and whether a
rocky soils and a diverse flora. In mid-May at species was at early, full, or late bloom. Notes
these locations we noted 25 or more plant were also made of species that had recently
species in flower simultaneously. Sagebrush passed out of bloom and of those that were
steppe at the remaining Yakima County sites aboutto come intobloom.
and the Grant County site fell within the Samples were collected by removing
standard-type zone (Taylor 1992), inflorescences or individual flowers with
characterized by moderately deep soil and scissors or pruning shears and immediately
vegetation dominated by grasses and tall placing them in 3.8L, self-sealing, plastic
sagebrush, Artemisia tridentata Nutt. bags. Care was taken when removing flowers
(Asteraceae). The Ing, Wells, and Alway sites to avoid dislodging insects and spiders. Since
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J.Entomol.Soc.Brit.Columbia108,December201 13
Table 1.
Sampling sites,habitattype ateach site, andsampling frequencies.
Sampling
frequency*
Site Location (county) Habitat 2002 2003
Hambleton 3.5 kmNTieton (Yakima) Sagebrush-steppe w w
4.J km JNNW lieton W W
Durey Sagebrush-steppe
(Yakima)
W
Sunset 4.5 km S Tieton (Yakima) Sagebrush-steppe I
3 km SSEUnion Gap W
Carlson Sagebrush-steppe I
(Yakima)
W
Leach 6 kmNNE Zillah (Yakima) Sagebrush-steppe I
W
Lynch 5.5 kmNEZillah (Yakima) Sagebrush-steppe I
W
Hattrup 5 km SSE Moxee (Yakima) Sagebrush-steppe I
6.5 km SSE Moxee W
Valicoff Sagebrush-steppe I
(Yakima)
W
USDA 18 km ESE Moxee (Yakima) Sagebrush-steppe I
Knutson 10 km SEMattawa (Grant) Sagebrush-steppe BW
M
Alway Peshastin (Chelan) Mixedhardwoods andconifers
2 km SSE HoodRiver M
Ing(Oregon) Mixedhardwoods and conifers
(Hood River)
6 km SSE HoodRiver M
Wells (Oregon) Mixedhardwoods and conifers
(Hood River)
W,weekly; BW, bi-weekly; M, Monthly; I, irregularly.
WFT
is primarily associated with flowers, less abundant species and those with small,
non-flower plant parts such as leaves and more difficult to collect flowers. Blooms were
stems were kept to a minimum in samples collected from several individual plants per
during the bloom periods. Samples taken species at a site to obtain a sample. The
outside ofthebloomperiod includedprimarily number of individual plants sampled per
rapidly growing vegetative tissue. Samples species depended upon the density of that
were transported in a cooled ice chest to the species at the site.
laboratory where they were held in a We were interested in each plant species
refrigerated room until processed, generally primarily during its bloom period. A single,
within 24 h. The amount of plant material flowering period sample was obtained for
collected for a sample varied from species to some species, but many were sampled more
species depending upon its abundance at a site than once during bloom. Several species were
and the nature of its inflorescence. Abundant sampled weekly while in flower with
species with large or bulky inflorescences additional samples taken during the pre-bloom
were collected in sufficient quantity to loosely and post-bloom periods. The extreme example
fill a bag. Smaller quantities were obtained of was bitterbrushPurshia tridentata (Pursh) DC
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14 J.Entomol.Soc.Brit.Columbia108,December201
(Rosaceae), which was sampled weekly at the ofadult WFT in the sample. Ifthe number of
Durey site from 16 April to 28 October 2003, thrips in a sample appeared to be less than
for a total of 29 sample dates. Most species 300, an exact count was made. For samples
were sampled at one or two locations, but that obviously contained a greaternumber, the
samples from arrowleaf balsamroot number ofthrips was estimated by counting a
Balsamorhiza sagitatta (Pursh) Nutt. subsample (an exception was made for the
(Asteraceae), a common, widespread species, maximum density from each plant species,
were obtained at nine sites. In 2002, most of which was always determined by an exact
the plant species at each site were sampled on count). To obtain estimates from subsamples,
at least one date. Based on the 2002 findings, the thrips (in alcohol) were poured into a
16 species that supported high numbers of plastic Petri dish inscribed on the bottom with
thrips andpredators were monitoredin2003. six squares each 1 cm x 1 cm in size. The dish
Extraction of arthropods. Thrips and was agitated until the thrips were distributed
predatory arthropods were extracted from approximately uniformly over the bottom of
plant material using Berlese funnels. Heat the dish. The thrips within each square were
from 40 watt light bulbs was used to force counted, the average number per square was
arthropods out of the plant material and into computed, and this average was multiplied by
500 ml plastic jars each containing 50 ml of the areaofthe dish to obtain anestimate ofthe
70% isopropyl alcohol. Samples were held in total.
the funnels for 24-48 h depending on the Exact counts were made of all predators.
quantity ofplant material. This length oftime For minute pirate bugs, Orius spp., the
was sufficient to dry the plant material, which numberofmales, females, andeach ofthe five
was then weighed on an electronic balance. nymphal instars was determined. Samples
We calculated thrips numbers per gram dry were composed almost entirely of Orius
weight ofplantmaterial. tristicolor (White, 1879), although scattered
Processing ofsamples. WFT was the only individuals of Orius diespeter Herring, 1966
thrips identified to species (by comparison were likely present in the Peshastin samples
with vouchers). Species other than WFT were (Lewis et al. 2005). Immature spiders of
generally few in number (see Results). Larval several species were common in some
thrips were counted but were not identified. samples. In most cases it was possible to
When the adult thrips in a sample were identify these to species based on our
exclusively WFT we assumed that all larval familiarity with the local fauna. It was also
thrips were that species. Ifadults ofmore than possible to estimate the nymphal stage of
one species were present the number oflarval many of these spiders based on comparison
WFT was estimated based on the proportion withreference specimens ofknown stage.
RESULTS
Host plant characteristics. One hundred species).
and thirty plant species were sampled, Host plant utilization by Frankliniella
representing 34 plant families and 101 genera occidentalis. Adult WFT were extracted from
(Table 2). Ninety-nine species were native to 119 plant species, while thrips larvae were
the study area, while 31 species were extracted from 108 ofthese same 119 species
introduced. The Asteraceae was represented (Table 2). Plant species that harbored both
by the most species (32), and the wild adult and larval WFT are assumed to be
buckwheat genus Eriogonum (Polygonaceae) reproductive hosts for the insect. Of the 11
was the best represented genus with seven species that did not yield WFT, eight were
species. Samples from red clover Trifolium sampled only once, five have rather small or
pratense L., white clover Trifolium repens L., inconspicuous flowers, and one blooms early
and alfalfa Medicago sativa L. (all Fabaceae) in the spring. Two ofthe species that did not
were collected only within orchards. Plant yield WFT, {Lomatium triternatum (Pursh)
growth form varied, but perennial forbs were Coult. and Rose and Erigeronpumilus Nutt.)
the most common (62 species) followed by had congeneric species that yielded both adult
shrubs (20 species) and annual forbs (16 WFTandlarval thrips. Itis likelythatmore
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J.Entomol.Soc.Brit.Columbia108,December201 15
Table 2
Plant species sampled for Frankliniella occidentalis (WFT) indicating presence (+) or absence (-) of
WFT and presumed WFT larvae. Max. WFT density is the maximum density (# ofadults plus larvae
per gram dry weight ofplant material) recorded for a plant based on an exact count. Abbreviations:
N=native species; I=introduced species; F=forb; H=herb; S=shrub; T=tree; V=vine; A=annual;
B=biennial; P=perennial.
WFT WFT
Plant Type of WFT No. of
Origin plant adults larvae samples
density
ACERACEAE
AcermacrophyllumPursh N T + 0.7 2
APIACEAE
DaucuscarotaL. I BF + + 0.2 1
LomatiumcolCuomnsbtiaanncuemMathiasand N PF + + 0.5 1
LomatiumgrayiCoult. andRose N PF + + 21.6 8
Lomatiumnudicaule(Pursh) Coult. N PF + + 0.2 2
andRose
Lomatium tritaenrdnaRtousme(Pursh)Coult. N PF - - 0 1
APOCYNACEAE
ApocynumandrosaemifoliumL, N PF + + 24.8 5
AsclepiasspeciosaTorr. N PF + + 255.9 8
ASTERACEAE
AchilleamillefoliumL. N PF + + 62.5 63
A(rn^pvi^ cflmicnrPiir<5li^Raf N PF + + 0.2 2
AmbrosiaavtemisiifoliaL. I AF + + 1.2 1
ArtemisiatridentataNutt. N s + + 30.4 80
AvIpwiiVin K.x\ N s + 5
Tinlvnyyirtyhiynhnnh'PviMiitt N PF 204
UTfiAlnij1f^AinfmiLn/rrfhiliZ7jinAi^jnicAr^liltLtUnltLnl (^\1^^L^lri'oii\\l\1Ni^>itiitltl. N PF 11 8 57
C^pyifnijvpnrvnnu^T I AF 4- 21.8 4
CentaureadiffusaLam. I A/BF + + 9.9 13
(^hnpnnpfiv/iratnuodlnAvmii.^T-Tr»nl<r^1-Tr»r»l<r N B/PF + + 29.1 14
Chrysothamnusviscidiflorus (Hook.) N S + + 58.7 84
Nutt.
Cirsiumarvense(L.) Scopoli I PF + + 34.4 12
i\^ilvf^iiMuidyryril Uurnl/i^AUnlltllUffl yilMWiXiVfXf,,)^ QOUr^IrC*fl=*ln^rr. "INNT -)- -(- 1 8 L9
\^iC-L/Il3 LiL'lifrllfliAlLl l^iUlll, NN PF + -I- 15 7 14
x^fyK^^Ln/litvj niJnL'nLi'/ICidctf^fnltlLnlllilij ^ITNiLiitltt, A/PF 4- -\- 0 7 A
CrocidiummulticauleHook. N AF + 11.4 1
Dieteriacanescens(Pursh)Nuttall N B/PF + + 17 10
EricameGr.iNaensaousmeaonsdaG(P.alBla,ierxdPursh) N S + + 132.2 76
Erigeronfilifolius(Hook.)Nutt. N PF + + 10.5 8
Erigeronlinearis(Hook.)Piper N PF + + 4.3 8
ErigeronpumilusNutt. N PF 0 1
Eriophyllum lanatum (Pursh)J. N PF + + 0.3 5
Forbes
HelianthuscusickiiA. Gray N PF + + 61.1 7
IvaaxillarisPursh N PF + + 107.2 7
1
16 J.Entomol.Soc.Brit.Columbia108,December201
WFT WFT Max.
Plant Type of WFT No. of
Hostplant
Origin plant adults larvae samples
uensiiy
LactucaserriolaL. T1 Ar u o
LayiaglandulosAam(.Hook.)Hook, and N AF + + 1.9 3
N PF + + 1.3 5
Greene
PyrrocomacarthamoidesHook. XJNT rr + + U.O 0o
Senecio integerrimusNutt. N BF + + 6.2 4
SoUdagolepidaDC N PF + + 35.5 15
Stephanomeriatenuifolia(Raf.)H. N PF + + 0.8 3
iVl. riail
Tragopogondubius Scop. I A/BF + + 13 8
BERBERIDACEAE
BerberisaquifoliumPursh N S + + 0.8 5
BORAGINACEAE
AmsincFiksicah.lyacnodpsCo.iAd.esMLeeyhmex N AF + + 36.8 8
AmsinckiatessellataA. Gray XT Ar + + 62.11 110A
CynoglossumgrandeDougl. ex N PF 0 2
Lehm.
LithospermumruderaleDougl. ex N PF + - 1.2 3
Lehm.
MertensialongifloraGreene N PF + + 1 2
BRASSICACEAE
ChorisporatensIla(Pall.)DC T At 1
Descuraniasophia(L.)Webb and I AF + + 25.1 5
Prantl
Erysimumcapitatum (Dougl. ex N B/PF + + 2.2 2
Hook.) Greene
LepidiumperfoliatumL. I A/BF + + 10.7 3
PhoenicaulischeiranthoidesNutt. N PF + + 7 1
SisymbriumaltissimumL. I A/BF + + 60.7 9
Thelypodium laciniatum(Hook.)
IN or
Endl.
CAPRIFOLIACEAE
Loniceraciliosa(Pursh)Poir. exDC. N PV - - 0 1
SambucusceruleaRaf. N s + + 31.7 4
Symphoricarposalbus (L.)Blake N s + + 6.2 8
CHENOPODIACEAE
Kochiascoparia(L.) Schrad. I AF + + 30.4 8
ChenopodiumalbumL. I AF + + 9 5
Grayiaspinosa(Hook.)Moq. XT c _i_ 11oQ.0Z 1(\
Sni'unln tfno'ij^T I AF + + 15.1 12
CLUSIACEAE
HypericumperforatumL. I PF + + 1.2 1
CORNACEAE
CornussericeaL. N S + + <0.1 2
FABACEAE
Astragalus sp. N PF + + 14.9 3
Cytisusscoparius(L.)Link I S + + 4.9 3
LupinuslepidusDougl. exLindl N PF + + 23 4
LupinuswyethiiWats. N PF + + 36.9 10
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J.Entomol.Soc.Brit.Columbia108,December2011 17
WFT WFT Max.
Plant Type of No. of
oosipiani Origin plant adults larvae VYr 1 samples
density
MedicagosativaL. I A/PF + + 138.7 14
Melilotusofficinalis (L.)Lam. I A/PF + + 178.2 19
IrlJOllurnmuCroCiipncllUTn\r\Xlhv\) N PF + + 1.9 2
Poir
TrifoliurnpratenscL. I B/PF + + 28.4 3
TrifoliumrepensL. I PF + + 128.4 22
GROSSULARIACEAE
RibesaureumPursh N S + + 0.9 1
RibescereumDougl. N S + + 1 2
HYDRANGEACEAE
PhiladelphuslewisiiPursh N S + + 89.4 7
HYDROPHYLLACEAE
PhaceliahastataDougl. exLehm. N PF + + 231.3 13
Phacelialinearis(Pursh)Holz. N AF + + 10.8 5
IRIDACEAE
OlsyniumdouglasiiA. Deitr. N PF - - 0 1
LAMIACEAE
Agastacheoccidentalis(Piper)Heller N PF + + 29.4 18
Salviadorrii(Kellogg)Abrams N S + + 17.6 2
TLITTL¥IAA^C¥7E"AAET?
AlliumacuminatumHook. N PF + + 25.8 2
/±spurugus ujjicinuiis l^. T PF zu.z. 1
CalochortusmacrocarpusDougl. N PF + + 1.9 1
TriteleiagrandiforaLindl. N PF + + 4.1 2
Zigadenusvenenosus S. Wats. N PF + _ 0.3 4
MTi/rAA.LTV\7AACEAATET"
opriuaruici^ugrussuiuriijoiiu^^^u^JK.. N PF + + 6.9 4
andAm.)Rydb.
Sphaeralceamunroana(Dougl ex N PF + + 40.1 3
Lindl.) Spachex Gray
ONAGRACEAE
Epilobium angustifoliumL. N PF + + 4 1
PLANTAGINACEAE
PlantagomajorL. I PF 0 1
rOACEAE
UiUfrlUiS It^ClUfUffl L^, Ti 11.1 1
SchedonorusaDruumnodritn.aceus (Schreb.) I PH 0 1
SecalecerealeL. I A/BH + + 1.8 1
POLEMONIACEAE
CollomiagrandifloraDougl. ex N AF + + 0.9 4
Lindl.
Ipomopsisaggregata(Pursh)V. Grant N B/PF + + <0.1 1
PhloxhoodiiRichards N PF + + 3.5 10
PhloxlongifoliaNutt. N PF + + 57.1 5
PhloxspeciosaPursh N PF + + 2.6 6
POLYGONACEAE
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18 J.Entomol.Soc.Brit.Columbia108,December201
WFT WFT Max.
Plant Type of WFT No. of
Origin plant adults larvae VtJ? 1 samples
density
EriogonumcompositumDougl. ex N PF + + 61.5 6
Benth.
EriogonumelatumDougl. N PF + 4- 150.9 86
EriogonumheracleoidesNutt. N PF + + 48.2 6
EriogonummicrothecumNutt. N PF + + 35.8 15
EriogonumniveumDouglas exBenth. N PF + + 23.4 7
EriogonumstriatumBenth. N PF + + 76.4 4
EriogonumthymoidesBenth. N PF + + 1.1 4
RumexcrispusL. I PF + + 12.9 7
RANUNCULACEAE
ClematisligusticifoliaNutt. N PV + + 77.1 28
DelphiniumnuttallianumPritz. ex IN rr + + u.y J
Walp.
RHAMNACEAE
Ceanothus intAegme.rrimusHook. & N s + 4.1 6
CeanothusvelutinusDougl. exHook. N s + + 0.1 2
Frangulapurshiana(DC.) Cooper N S/T + + 2.5 2
ROSACEAE
Amelanchieralnifolia(Nutt.)Nutt. ex N S/T + + 0.4 6
M. Roemer
CrataegusaouglasiiLindl. N S/T + <0.1 2
Holodiscusdiscolor(Pursh)Maxim. N S + + 40.3 3
Prunusavium (L.)L. I T + + 11.2 4
Prunusemarginata(Dougl. exHook.) N S/T + + 0.5 2
D. Dietr.
PrunusvirginianaL. N S/T + _ 1.4 4
Purshiatridentata(Pursh)DC N S + + 18.7 71
RnosawoodJsI•TLi1ndl11. N s + + 88.7 11
RubusarmeniacusFocke T1 o/V 9'^ A A
RUBIACEAE
GaliumaparineL. >i>J /A\Fr nu 11
SALICACEAE
N S/T + 57.7 15
SANTALACEAE
Commandraumbellata(L.)Nutt. N PF + + 0.9 7
SAXIFRAGACEAE
HeucheracylindricaDougl. exHook. N PF + - 0.6 2
Lithophragmaparviflorum (Hook.)
N PF 0 2
Nutt.
oV^lVVyir11\J /AIv1/A 11*r\11/
CastillejathompsoniPennell N PF + + 34.1 9
CollinsiaparvifloraLindl. N AF 0 1
Linariadalmatica(L.)Mill. I PF + + 1.2 2
PenstemonhumilisNutt. exGray N PF + + 8.8 6
Verbascum blattariaL. I BF + 0.1 1
Verbascum thapsusL. I BF + <0.1 2
URTICACEAE
UrticadioicaL. N PF + + 9.3 1
1)
J.Entomol.Soc.Brit.Columbia108,December201 19
intensive sampling wouldhave foundWFT on between early-April and mid-October (Fig. 1).
bothL. triternatum andE.pumilus. Species that bloomed early included
Frankliniella occidentalis reached very Balsamorhiza sagittata and other forbs. Late-
high densities on some host plants, exceeding flowering species included Chrysothamnus
100 individuals per gram dry weight ofplant viscidiflorus (Hook.) Nutt. (Asteraceae) and
material in samples from eight species (Table Eriogonum microthecum Nutt. (Polygonaceae)
2). Many of our nearly 1200 samples (Fig. 1). One plant species, Eriogonum
contained several thousand thrips. For elatum, had a very long flowering period, first
example, an exact count ofthrips from an 86.2 showing blooms in late-June and flowering
g sample of flowering Ericameria nauseosa well into October (Fig. 1).
(Pall, ex Pursh) G. Nesom and G. Baird WFT was present, often in large numbers,
(Asteraceae) yielded 10,320 adult WFT, 26 throughout the sampling period at these sites
unidentified adult thrips, and 1,079 larvae. A (Fig.l). Generally, WFT occurred at only low
25.2 g sample offloweringAsclepias speciosa densities on plants in the weeks preceding
WFT
Torr. (Asclepiadaceae) produced 5,503 adult bloom. density increased during the
WFT, 26 unidentified adults, and 951 larvae. flowering period, and larval thrips greatly
This was the highest density recorded during outnumbered adults in some samples from
the study, at 255.9 WFT per gram of plant some plant species. For example, a peak
tissue. WFT was by far the most abundant bloom sample from Phacelia hastata Dougl.
species ofThysanoptera on the majority ofthe ex Lehm. (Hydrophyllaceae) yielded 297
hostplants sampled during this study. Samples WFT adults and 2594 thrips larvae. Post-
from Eriogonum elaturn Dougl. bloom densities of thrips were usually low,
(Polygonaceae) (86 samples over two years) and the near disappearance of the insect
yielded 26,255 total adult thrips and 61,162 during the immediate post-bloomperiod could
larvae. Only an estimated 143 adults (<1%) be rapid (see also section on thrips and
werenotWFT. predator phenology, below). The perennial E.
These other thrips included a species elatum was notable for its lengthy flowering
tentatively identified as another Frankliniella. period and relatively high densities of thrips.
This thrips occurred on most Asteraceae and Throughout the flowering period WFT was
in some samples equaled or exceeded WFT in present at densities as high as 150.9 per gram
number. The most extreme example was dry weight of E. elatum plant material.
Pyrrocoma carthamoides Hook. (Asteraceae). Densities on E. elatum remained high well
This plant was sampled for eight consecutive into October when most other plant species
weeks in 2002 fromthe pre-bloom stage to the had passed out of bloom (Fig. 1). From late
post-bloom stage. Although WFT was found June to late September larvae usually
in each sample it was greatly exceeded in outnumbered adults and comprised up to 90%
abundance by the second putative of a sample. Since WFT were virtually the
Frankliniella species. Other genera of only adult thrips in our samples most larvae
Thysanopterawere also abundant on occasion. were undoubtedly this species. Thus E. elatum
A species of Haplothrips (probably appears to be an excellent reproductive host
Haplothrips verbasci (Osbom, 1897); Horton forWFT.
and Lewis 2003) was dominant on Verbascum Shrubs, which remain relatively green and
thapsus L. (Scrophulariaceae). A sample of V. succulent throughout the season, often
thapsus late in its 2002 flowering period supported WFT even when not in flower.
yielded 1040 Haplothrips (adults and larvae) Chrysothamnus viscidiflorus, Ericameria
but only fourWFT. nauseosa, and Artemisia tridentata flower in
Plant phenology and thrips counts. We late-summer or fall, but pre-bloom samples as
present phenology data from two extensively early as mid-May from all three species
sampled sites (Durey andHambleton; Table 1 yielded WFT adults and thrips larvae at low
west of Tieton (Fig. 1); the two sites are densities (<1.0/gram dryweight).
separated by approximately 1 km. Plant Purshia tridentata presented an interesting
diversity was high in the habitat adjacent to case. Purshia flowers heavily for about four
the orchards at both sites. Plants in flower weeks in late-spring (Fig. 1). WFT density
were present at the two sites on all dates peaked late in the flowering period or during
1
20 J.Entomol.Soc.Brit.Columbia108,December201
WFT
early post-bloom and then declined gradually highest densities were recorded had
overthe next several weeks. From mid-July to flowering periods lasting a minimum of four
early-September it was present at very low weeks. A second factor that may contribute to
densities, and no adults were found in some high Orius and WFT densities on some plants
samples. Then, in mid-September, adults may be flowering phenology. Chrysothamnus
began to show up in increasing numbers and viscidiflorus, Ericameria nauseosa, and
were present through the end ofOctober (Fig. Artemisia tridentata flowered during late
1), despite the absence ofblooms. These late summer and fall. This phenological pattern
season individuals were almost exclusively may have tended to concentrate insects on
females. WFT was found in the surface soil these plants because fewer species are in
and litter beneath Purshia shrubs in late flower so late inthe season(Fig. 1).
autumn, apparently in preparation for Orius phenology appeared to track bloom
overwintering (unpublished observations). and thrips phenology. The phenologies ofthe
Predators of Frankliniella occidentalis bloom, the WFT, and Orius on three plant
and predator phenology. Minute pirate bugs species chosen because of differences in
(O. tristicolor) were the most abundant thrips flowering times are compared in Figure 2:
predators collected. Adult and/or nymphal Achillea millefolium L. (Asteraceae) (early
pirate bugs were collected from 64 host plants bloom), Chrysothamnus viscidiflorus (late
(Table 3) all ofwhich also hosted WFT. Orius bloom), and Eriogonum elatum (season-long
generally attained its highest densities on host bloom). The samples were obtained at the
plants that also supported high densities of Hambleton site in 2002. Densities of Orim
WFT, such as Achillea, Medicago, appeared to peak during bloom, and at orjust
Eriogonum, Clematis, and Trifolium (Tables 2 following peak numbers of thrips (Fig. 2\
and 3). Plants on which both insects reached Densities of both insect species declined
high densities tended to have long flowering rapidly followingbloom. InFigure 3, we show
periods, and 18 ofthe 20 species on which the age structure ofthe Orius specimens for each
Ehog. microth. -
Chrysothamnus -
Eriog. elatum -
Iva -
Crepis - X Nothripsinsample
Allium - ® 0-5thripsperg
Eriog. compos. -
5-10thripsperg
Agastache -
#
Phacelia - 10-20thripsperg
Achillea - ^^^^ >20thripsperg
Erigeron -
Purshia - ®®®®® ®X®XXX ®xx® ®®# ©® ®
Castilleja -
Amsinckia -
Lupinus -
Balsamorhiza -
April May June July Aug Sept Oct
Figure 1. Flowering periods (shaded bars) of selected WFT host plants based on the Durey and
Hambleton sites near Tieton, WA, and densities of WFT in pre-bloom, bloom, and post-bloom
collections. Mostplant species occurredatboth sites.