Phenology of western flower thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) on plant species in and near apple orchards in Washington State

2007·5 MB·English

by  S D Cockfield

J.Entomol. Soc. Brit.Columbia 104,December2007 35
Phenology ofwestern flower thrips Frankliniella occidentalis
(Pergande) (Thysanoptera: Thripidae) on plant species
in and near apple orchards in Washington State
S.D. C0CKFIELD\ E.H. BEERS^ and R.S. ZACK^
ABSTRACT
Both orchard and adjacent native vegetation harboured aduh western flower thrips,
Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), from early spring until
fall. Frankliniella occidentalis made up the great majority ofadults collected in flowers
ofmost plant species sampled, including apple. Other species found on apple flowers
includedAnaphothrips obscurus Miiller, which lives on grasses, and Thrips brevipilosus
A
Moulton. mixture of thrips species, including F. occidentalis, Scirtothrips citri
(Moulton), Thrips tabaci Lindeman, and Thrips treherni Preisner, occurred on apple
shoots. Thrips were found in orchards as early as green tip (earlyApril), withthehighest
concentrations ofF. occidentalis in shoots occurringinJune andJuly. Thrips declined in
late summer as shoots formed dormantbuds; however, someF. occidentalis adults were
still found in early September. Five common woody plants and forbs selected for sam-
pling in the sagebrush-steppe habitat had F. occidentalis adults present, especially dur-
ing bloom. Western flower thrips can exploit open flowers oryoung shoots from spring
through fall in native vegetation because of the diversity ofplants and their different
growthhabits.
INTRODUCTION
Western flower thrips, Frankliniella 1991, Beers et al. 1993). Oviposition sites
occidentalis (Pergande) (Thysanoptera: on fruit develop scar tissue surrounded by a
Thripidae), is native to western North larger, pinkish-white surface discoloration
America, where it has long been a crop pest called a pansy spot. This damage is most
(Bailey 1940). In the latter half of the apparent on green or light-coloured apple
1900s, it spread to various crops, green- cultivars (Venables 1925); not all cultivars
house cultures, and native plants in other show the damage at harvest. After flowers
areas of North America, where it became are no longer available, additional genera-
one of the most common thrips species tions develop in the apical portions of
(Felland et al. 1993, Chellemi et al. 1994). growing apple shoots (Venables 1925).
During the same period it also spread to The cause of pansy spot was unknown
native and cultivated habitats throughout formany years after it was first noted in the
the world (Kirk and Terry 2003). Frank- early 1900s, until Newcomer (1921) made
liniella occidentalis is attracted to showy, detailed observations and found thrips to be
fragrant flowers ofnumerous species (Terry the cause. However, in the original work,
1997), but also feeds on wheat (Toapanta et the species was not identified. Venables
al. 1996). (1925) was the first to identify the species
Frankliniella occidentalis is a pest of associatedwith apple. AlthoughF. occiden-
apple, where it oviposits on developing talis is cited as the most likely cause of
fruitlets around the flowering period (Terry injury to apple, Venables also found Aeo-
'TreeFruitResearch andExtensionCenter,WashingtonStateUniversity, 1100N. WesternAvenue,
WA
Wenatchee, 98801
WA
^DepartmentofEntomology, WashingtonStateUniversity, 157 FoodNutritionBldg.,Pullman,
99164-6382
36 J.Entomol.Soc.Brit.Columbia 104,December2007
lothrips fasciatus (L.), A. conjunctus Per- (1966), who sampled thrips on a variety of
gande, and Taeniothrips sp. He notes, how- native plants commonly found near apple
ever, that the latter species are likely preda- orchards in the dry interior valleys ofBrit-
cious on F. occidentalis. Childs (1927) ish Columbia. They concluded thatF. occi-
positively implicated both F. occidentalis dentalis moves from host to host as the
and A. fasciatus as causing injury, even plants flower. In addition, they note the
though he later notes that A. fasciatus was overlapping species complexbetween apple
supposed to be predacious and was not and native hosts. However, they present
common. Madsen and Jack (1966) list F. only a list of thrips species collected from
occidentalis, Rhopaloandrothrips corni various plant hosts, without temporal or
Moulton, Thrips hukkineni Priesner (=7. quantitative information. Further studies
trehernei Priesner), Thrips tabaci Linde- were conducted in the mid-1990s (Pearsall
man, Haplothrips niger Osborne, and Lep- and Myers 2000a, 2000b, Pearsall and
tothrips mali (Fitch) as occurring on apple, Myers 2001) that examined thrips ecology
with the latter two species as probable and dispersal in orchards nearnative habitat
predators. The leaf-feeding species T. in central British Columbia. These authors
tabaci was considered a visitor from grass concluded that thrips abundance in nectar-
hosts. Pearsall and Myers (2001) note that ine orchards was related to dandelion den-
12 species ofthrips were found in nectarine sity, and to proximity ofnative habitat. The
orchards in central British Columbia, Can- role ofweeds on the orchard floor and na-
ada, again with F. occidentalis as the most tive plants in extra-orchard habitats has not
common species. An investigation of the been investigated in central Washington.
species inhabiting apple has not been done This information is foundational to the de-
in the fruit-growing regions of central velopment of effective pest management
Washington. strategies.
The possible influence of plant species The workhereinhas two objectives. The
in or near the orchard on potential damage first objective is to determine the species of
by thrips was first suggested by Venables thrips adults in apple flowers and shoots in
(1925). He noted that alfalfa was a host, central Washington state. The second is to
and that its common use as a cover crop determine if and when selected weed and
might contribute to thrips damage. This native plant species are inhabited by the
idea was expanded by Madsen and Jack adults.
MATERIALS AND METHODS
Four 'Granny Smith' apple orchards ster, and Bridgeport, were adjacent to sage-
near the towns of Vantage (Kittitas brush-bunchgrass steppe. These areas had a
County), Orondo (Douglas County), Brew- mixture of grass species, including blue-
ster (Okanogan County), and Bridgeport bunch wheatgrass, Agropyron spicatum
(Douglas County) in central Washington (Pursh) Scribn. andJ. G. Smith, andneedle-
were selected as study sites and sampled in grass, Stipa spp. Forbs and woody plants
2002. All sites were typical of apple or- included arrowleaf balsamroot, Bal-
chards in the Columbia River valley in that samorhiza sagittata (Pursh) Nutt., lupin,
they were irrigated regularly to maintain Lupinus spp., big sagebrush, Artemisia tri-
fruittrees in a climate that receives an aver- dentata Nutt., and snow buckwheat,
age of 30-50 cm of precipitation per year, Eriogonum niveum Douglas ex Berth.
the majority as snowfall. Orchards were Patches of plants characteristic of higher
borderedby native vegetation on one ortwo elevations were also present, such as west-
sides. None of the sites was near riparian em yellow pine, Pinusponderosa P and C
habitat. Lawson, and antelope bitterbrush, Purshia
The three northern sites, Orondo, Brew- tridentata (Pursh) DC. The orchards were
J.Entomol.Soc.Brit.Columbia 104,December2007 37
irrigated by sprinklers and had a stand of Apple trees. As soon as the apple buds
Italian ryegrass, Lolium multiflorum Lam. started to grow (green tip), 100 buds were
(Orondo site), orchardgrass, Dactylis glom- taken weekly, or during bloom, twice per
erata (L.) (Bridgeport site), or weedy spe- week, from each site. Flower bud samples
cies such as downy brome, Bromus tecto- and vegetative bud samples were taken
rum L. (Brewster site). All three sites had a separately. From king bloom to petal fall,
mixture of broadleaf weed species on the 100 individual flowers, or, after petal fall,
orchard floor, including dandelion. Tarax- king fruit, were sampled. Vegetative bud
acum officinale G. H. WeberexWiggers. samples were taken from actively growing
The Vantage site, the farthest south, was shoots throughout the summer. These be-
bordered by rocky soil and talus. Grasses came scarce as the shoots completed
included bluebunch wheatgrass and growth later in the year. Sampling ended
sandberg bluegrass, Poa secunda J. Presl. when growing tips could no longer be
Forbs and woody species included phlox, found, by late summer. A sample of20 dor-
Phlox spp., daisy, Erigeron spp., big sage- mant shoots was taken at each site in Octo-
brush, and gray rabbitbrush, Chrysotham- ber.
nus nauseosus (Pallas) Britt. The orchard Ground cover. The two most common
was drip-irrigated and the soil surface was plant species onthe orchard floor, one grass
dry for most of the summer. The ground species and one broadleaf weed, were se-
cover included dry-adapted species such as lected for sampling. The most common
downy brome and flixweed, Descurania species varied by site. Grasses included
Sophia (L.) Webb, exPrantl. Italian ryegrass, orchardgrass, and downy
The Orondo site was under organic brome. Broadleafweeds included dandelion
management. No insecticides were used and flixweed. Four replicate samples per
other than horticultural oil. All the other site were collected weekly. Samples con-
orchards were under conventional pest sisted ofindividual plants cut offat ground
management. The Brewster site received no level, or when the plants were too large for
pesticides for thrips, and only azinphos- the sample bags, the flower stalks or
methyl during May through August. The crowns containing the youngest leaf tissue
Bridgeport site was treated with formetan- were selected. Sampling was discontinued
ate hydrochloride for thrips at full bloom, when the above-ground plant parts had
then pyriproxyfen and methoxyfenozide for dried due to dormancy, or in the case of
lepidopteran pests. The Vantage site was annuals, had gone to seed and dried. Sam-
treated with horticultural mineral oil and pling began again when winter annuals be-
chlorpyrifos at green tip, and spinosad for ganto sprout in the fall.
thrips at full bloom. Sagebrush steppe. Three to four ofthe
The objective of sampling was to count most common species ofplants in the sur-
adult thrips, presumed to be primarily F. rounding native vegetation were selected in
occidentalis, concentrated on the preferred the beginning for sampling. Four replicate
tissue (flowers and very young leaves) of samples were taken weekly. One of the
the various plant species. Beginning in species was a grass and the others were
early March, after the snow had melted, forbs or woody plants. Grasses included
samples were taken from apple trees, se- bluebunch wheatgrass, sandberg bluegrass,
lected plants in the orchard ground cover, and needlegrass. Other plants included gray
m
and plants located 10-50 into surround- rabbitbrush, big sagebrush, antelope bitter-
ing uncultivated native vegetation. All sam- brush, arrowleaf balsamroot, and snow
ples were collected, placed in 15 x 15 cm buckwheat. The sampling methods for
self-sealing plastic bags, and immediately grasses were the same as for those on the
stored in a cooler. Additional details of orchard floor. For large forbs and woody
sampling procedures are described by habi- species, several shoot cuttings, about 15 cm
tat. long, were collectedin sufficient quantity to
38 J.Entomol. Soc.Brit.Columbia 104,December2007
fill a sample bag. Ifavailable, cuttings with The small number of species was sent to
actively growing leaves or flowers were Cheryl O'Donnell, Department ofEntomol-
selectedpreferentially overdormant ornon- ogy, University ofCalifornia, Davis, CA, as
flowering shoots. vouchers for identification. Adult Frank-
Extraction of thrips. Thrips were sepa- liniella specimens from apple shoots and
rated from the plant material by filling the other plant species were slide-mounted and
sample bag with water, adding a few drops identified to species. A representative sam-
ofliquid detergent, and agitating for several ple ofthe other species on apple shoots was
seconds. Thrips and plant material were also slide-mounted and sent to Cheryl
separated from the soapy water by pouring O'Donnell foridentificafion.
through two sieves (Hubbard Scientific Co., Most of the samples contained fewer
Northbrook, IL). The larger sieve (#10, than 50 specimens. However, a few sam-
mm
0.25 mesh) trapped most of the plant ples, especially those from dandelion, con-
material, and the finer sieve (#230, 0.0014 tained an unusually high number ofthrips,
mm
mesh) trapped the thrips (Lewis et al. often exceeding 150. Ifthe number ofadult
1997a) Thrips were then rinsed into a vial thrips exceeded 50, the total was recorded,
of50%ethanol. and half of the specimens were randomly
Adult and larval thrips were counted selected fora subsample. The original num-
separately. Adult specimens from apple bers of F. occidentalism other species, and
flowers were all slide-mounted in PVA other unidentified thrips were estimated by
Mounting Medium (BioQuip Products, Inc., dividing the numbers in the subsample by
Rancho Dominiguez, CA) and identified. the proportionofadults selected.
RESULTS
Apple trees were still fully dormant phothrips obscurus Miiller, a species found
when sampling began in early March. on grasses (Lewis et al. 1997b), made up
When the apple buds reached green tip, 8.9%. Thrips brevipilosus Moulton, a spe-
about the second week in April, adult thrips cies originally collected from native forbs,
beganto appearinthe shoots (Fig. 1). Adult potential orchard weeds such as alfalfa and
thrips were present in the opening apple wild mustard, and a species of Artemisia
flowers as petals began to unfurl (pink) (Moulton 1927), made up the remaining
(Brewster, Bridgeport, and Vantage sites) 0.8%). Frankliniella occidentalis comprised
or by the time the first flowers in the clus- a little more than one-third of the adults
ters had fully opened (king bloom) (Orondo collected from apple shoots (Table 1).
site). Larvae were also foundatkingbloom. Thrips treherni made up \2.1% of speci-
By full bloom, both adults and larvae were mens, while Scirtothrips citri (Moulton)
abundant. Insecticide applications and T. tabaci together made up most ofthe
(formetanate hydrochloride and spinosad) remaining49.5%).
reduced the numbers of adults and larvae, Thrips numbers in apple shoots were
but only temporarily. Although thrips at the low during bloom, then greatly increased at
Vantage site may have been affectedby the petal fall (mid-May) (Fig. 1). No apparent
chlorpyrifos application at green tip, adults break occurred between one generation and
were found in blossom clusters by pink. the next. The highest concentrations of F.
Adults and larvae declined after full bloom, occidentalis in shoots occurred in June and
but a few were still present at the end ofthe July. Larvae outnumbered adults in May,
blossom period. Some thrips were recov- June, and part of July. Adult and larval
ered fromyoung fruit atpetal fall. populations declined in late summer as
Frankliniella occidentalis made up the shoots formed dormant buds; however,
great majority (90.3%) of the adults col- some F. occidentalis were still found in
lected in apple flowers (Table 1). Ana- early September (Fig. 1). Samples of the
J.Entomol. Soc.Brit.Columbia 104,December2007 39
r
12
bloom-
10 Appleflov^rs
8
6
4
2
0
12
Appleshoots
10
8 •-shootgrowth—
6
4 AO 8 ° ? o
2
0
0) 12
t 10 Downybrome
I « —
bloom--
A germination
A A A A A A A A ^
,
40 1 1 1 1 1 1 1
Flixweed
30 -—bloom-—
A
20
A
10
0 -.AA A A-aAa_A
Dandelion
-—bloom-
150
100 -
0°0
O
50 - o o
0
1-Mar 1-Apr 1-May 1-Jun 1-Jul 1-Aug 1-Sep 1-Oct 1-Nov
Figure 1. Adult Frankliniella occidentalis (solid symbols) and other thrips species combined
(open symbols) found in plant samples in orchards near Brewster (•), Vantage (A), Bridgeport
(), and Orondo () in 2002. Periods ofplant growth are indicated with dashed lines. A gray
background shows a period when samples were not taken. Samples with zeros are not repre-
sented. Arrows indicate the date ofapplication ofchlorpyrifos at the Vantage site (pre-bloom)
andformetanatehydrochloride orspinosad atthe BridgeportandVantage sites (fullbloom).
dormant buds in October yielded a few found on both species in the fall. Frank-
specimens ofother species atone site. liniella occidentalis adults were found on
Few thrips specimens were found in downy brome both in very early spring and
orchardgrass or Italian ryegrass, and no F. when new plants germinated in September
occidentalis adults were found on these (Fig. 1, Table 1). Moderate numbers oflar-
species. A few unidentified larvae were vae were also found in very young downy
40 J.Entomol.Soc.Brit.Columbia 104,December2007
Table 1.
Percentage ofadult Frankliniella occidentalis in collections from plants at different stages of
growth.
Plant Type ofsample Number Total adult P nrciHpfitnli^
ofsamples thrips (%)
apple flowers 116 124 90.3
shoots 368 932 37.8
dandelion floweringplants 263 8058 9.1
downybrome springplants 126 47 19.5
fallplants 52 40 20.0
flixweed prebloom 46 4 75.0
bloom 20 329 96.4
arrowleafbalsamroot prebloom 12 2 0.0
bloom 24 521 47.0
antelopebitterbrush bloom 32 22 64.3
shootgrowth 176 73 12.3
Gray rabbitbrush prebloom 84 26 7.7
bloom 52 967 83.3
snowbuckwheat prebloom 167 12 41.7
bloom 92 568 86.3
big sagebrush prebloom 283 113 14.2
bloom 112 628 89.2
brome. sampled from March through the end of
Flixweed, a yellow-flowered winter apple bloom (mid-May) had a low concen-
annual, was common at the Vantage site. tration ofthrips, although the flowers were
This plant flowered for about six weeks abundant. Some F. occidentalis were found
after apple bloom. Frankliniella occiden- in dandelion flowers throughout the grow-
talis was found on the flowers until it was ing season, however, other species were
mowed in late May (Fig. 1). Afterward, more abundant (Table 1), especially T. tre-
thrips were less abundant on flixweed and hemi. From mid-May until late September,
declined until the plant went to seed and T. treherni were highly concentrated in the
dried, around late June. few open flowers, with dozens of adults
Dandelion bloom began in April and occurring on a single plant. By late summer
lasted until frost, but peak bloom occurred and fall, very few larvae were found, and
in April and early May, declining just be- thripspopulations decreased in October.
fore peak apple bloom. Some dandelion Arrowleafbalsamrootbegan to bloom at
plants had over 10 flowers opened at peak this site in early May, and thrips, including
flowering. Most dandelions did notproduce F. occidentalis, were abundant in the flow-
flowers after May, but about 1% could be ers (Fig. 2). Many larvae and a few adultF.
found on any one sample date with a single occidentalis were found on bitterbrush in
floweruntil frost. Frankliniella occidentalis early May, when the plant was in bloom
were present on dandelion before apple (Fig. 2). Few thrips were found on the plant
trees broke dormancy (Fig. 1). Dandelions as its fruit matured in mid-May to mid-
— —
J.Entomol. Soc. Brit.Columbia 104,December2007 41
1 1 r
Arrowleafbalsamroot
—
-- bloom
1 1
Antelope bitterbrush
bloom- shootgrowth
E0G)l 20 |- Gray rabbitbrush bloom
(0
15
Q.
10
5
A A ^ A A A A A AA
1 1
Snowbuckwheat bloom
—
— —
0 <M>- -o <^>—0.
1 r r
Big sagebrush
bloom
(A
1-Mar 1-Apr 1-May 1-Jun 1-Jul 1-Aug 1-Sep 1-Oct 1-Nov
Figure 2. Adult Frankliniella occidentalis (solid symbols) and other thrips species combined
(open symbols) found in plant samples ofnative vegetation adjacent to orchards near Brewster
(•), Vantage (A), Bridgeport (), and Orondo () in 2002. Periods ofplant growth are indicated
with dashed lines. A gray background shows a period when samples were not taken. Samples
withzeros arenotrepresented.
June. When bitterbrush began to grow new when shoots were growing in the summer,
vegetative shoots in late June to fall, both and those collected were species other than
adults and larvae were found. These were F. occidentalis (Fig. 2). Flowerheadsbegan
mostly other thrips species, but a few F. to form on big sagebrush in July, and by
occidentalis were collected(Table 1). September and October, thrips were abun-
Very few thrips occurred on snow buck- dant on the open flowers. Adults were
wheat, big sagebrush, and gray rabbitbrush found first, followed by larvae 1-2 weeks
42 J.Entomol.Soc.Brit.Columbia 104,December2007
later. Gray rabbitbrush and snow buck- grass, sandberg bluegrass, and needlegrass
wheat also attracted thrips to their flowers, had very few thrips and no F. occidentalis
including F. occidentalis (Fig. 2, Table 1). werecollected.
Native grasses such as bluebunch wheat-
DISCUSSION
In Washington, F. occidentalis was the After petal fall, F. occidentalis adults
most numerous adult thrips and was most joined a mixture ofspecies in apple shoots
likely the predominant species ovipositing from early spring until late summer. This
in apple flowers. They produced most of season-long presence on apple trees, al-
the fruit injury, and the abundant larvae though alluded to by Venables (1925), has
found at king bloom and later. Thus, or- gone largely ignored and unstudied since
chard management aimed at reducing num- that time. Adults can also move to flixweed
bers of this species is key to minimizing when it flowers briefly after apple bloom
pansy spot. A. obscurus, also recovered from mid-May to mid-June, or return to
from apple flowers, is a specialist on dandelion, which maintains limited flower-
grasses (Lewis et al. 1997b) and highly ing throughout the summer and fall. Thrips
unlikely to oviposit in apple blossom clus- trehernei was the most common species on
ters. Thrips brevipilosus, rare in our sam- dandelion in Washington, echoing the find-
ples, has not been collected on apple previ- ings in British Columbia (Madsen and Jack
ously and may have been reproducing on 1966, Pearsall and Myers 2001). In early
weeds (Moulton 1927). fall, F. occidentalis adults can move to
Frankliniella occidentalis is considered young downy brome. Thus, F. occidentalis
to be highly nomadic (Terry 1997) and can continuously inhabit apple orchards.
movement from plant to plant likely ex- All plant species selected for sampling
plains much of the fluctuations in popula- in the sagebrush-steppe habitat, except the
tion density. The sequence ofmovement in grasses, had F. occidentalis adults present,
apple orchards can be inferred from the especially duringbloom.Frankliniella occi-
phenology on individual hosts. Frank- dentalis has been collected on almost every
liniella occidentalis overwinters as mated flower sampled from western orchards and
adult females in leaf litter and on the bark surrounding vegetation (Madsen and Jack
oftrees (Pearsall and Myers 2000a). Adults 1966, Pearsall and Myers 2000a). Thrips
begin emerging in early March and con- can probably find open flowers or growing
tinue emerging for six weeks (Pearsall and shoots throughout the year in native vegeta-
Myers 2000a). In Washington orchards, the tion because of the diversity of plant spe-
earliest plants attractive to adults include cies andtheir different growth habits. There
downy brome and dandelion. As soon as are a few gaps in the phenology of plants
apple trees begin to grow, they attracted a sampled in this study when concentrations
few adults to flowering as well as vegeta- of F. occidentalis adults could not be lo-
tive buds. Adults concentrated in apple cated, namely March to early April, and
flowers after the petals began to open, the June through July. Some common species
corolla colour changed from pink to pink not sampled were observed blooming in
and white, and flowers released fragrance. March, such as bluebell, Mertensia
Adults of this anthophilous species were longiflora Greene, and sagebrush buttercup.
most likely drawn to apple and other host Ranunculus glaberrimus Hook. Plant spe-
flowers based on a combination of colour cies other than those sampled in our study
and fragrance (Terry 1997). In addition, the could be found blooming in June and July,
magnitude and timing ofmigration to apple such as lupin, Lupinus spp., and desert
flowers may have been in response to tem- buckwheat, Eriogonum spp., and could be
perature (Pearsall andMyers 2000a). important in the population dynamics ofF.
J.Entomol.Soc. Brit.Columbia 104,December2007 43
occidentalis. Pearsall and Myers (2001) dentalis adults in their flowers, may attract
caught most F. occidentalis on sticky cards F. occidentalis out of orchards when in
placed in sagebrush steppe during March, bloom in the fall. Migration in and out of
late April to early May, and again in Sep- orchards has not been studied and remains
tember. Two ofthese periods correspond to critical to understanding the phenology and
the blooming of arrowleaf balsamroot and population dynamics ofthis species.
big sagebrush, which may be the cause of Reduction ofweedy hosts has been sug-
increased flight or abundance. Thus, much gested as an integral part ofmanagement of
ofthe population dynamics can be inferred F. occidentalis in orchards (Venables
by plant to plant movement within this 1925). However, our samples indicated
habitat. relatively low numbers of thrips in two
The possibility remains that F. occiden- abundant weeds, downy brome and dande-
talis migrates between native, dry habitats lion, before apple bloom. The apple trees
and orchards during periods ofsparse shoot themselves harboured adults throughout the
growth or bloom. For example, fruit trees growing season, as did numerous other
appear to attract thrips into orchards in plant species in and adjacent to orchards.
spring (Pearsall and Myers 2001). Alterna- Thus, indirect management of this pest
tively, the woody species big sagebrush, through reduction of any one plant species
gray rabbitbrush, and snow buckwheat, mayprove challenging.
which had a high concentration ofF. occi-
ACKNOWLEDGEMENTS
We thank Cheryl O'Donnell, Depart- Schaub for lab assistance in mounting
ment ofEntomology, University ofCalifor- thrips, and Diana Johnson for help with
nia, Davis, CA, for identification ofspecies counts. This research was funded in part
in the reference collection, and for helpful through a grant from the Washington Tree
information on the preservation and identi- FruitResearch Commission.
fication of thrips. We also thank Angela
REFERENCES
Bailey, S.F. 1940. The distribution ofinjurious thrips in the United States. Journal ofEconomic Entomol-
ogy33: 133-136.
Beers, E.H., J.F. Brunner, M.J. Willet andG.M. Warner(eds.). 1993. Orchardpestmanagement: aresource
bookforthePacificNorthwest.GoodFruitGrower,Yakima,WA.
Chellemi, D.O., J.E. Funderburk and D.W. Hall. 1994. Seasonal abundance of flower-inhabiting Frank-
liniella species (Thysanoptera: Thripidae) on wild plant species. Environmental Entomology 23: 337-
342.
Childs, L. 1927. Two species ofthrips injurious to apples in the Pacific Northwest. Journal ofEconomic
Entomology20: 805-809.
Felland, CM., L.A. Hull, D.A.J. Teulon and E.A. Cameron. 1993. Overwintering ofwestern flowerthrips
(Thysanoptera: Thripidae)inPennsylvania.TheCanadianEntomologist 125: 971-973.
Kirk, W.D.J, and L.I. Terry. 2003. The spread of the western flower thrips Frankliniella occidentalis
(Pergande).Agricultural andForestEntomology5: 301-310.
Lewis, T., L.A. Mound, S. Nakahara and C.C. Childers. 1997a. Field and laboratory techniques, pp. 435-
476.InT. Lewis(ed.),Thripsascroppests. CAB International,NewYork,NY.
Lewis, T., L.A. Mound, S. Nakahara and C.C. Childers. 1997b. Appendix II majorcrops infestedbythrips
with main symptoms and predominant injurious species, pp. 675-709. In T. Lewis (ed.), Thrips as crop
pests. CAB International,NewYork,NY.
Madsen, H.F. and I.D. Jack. 1966. Therelation ofthrips to pansy spot on apples. The Canadian Entomolo-
gist98: 903-908.
Moulton, D. 1927. Thysanoptera~ new species andnotes. Bulletin ofthe BrooklynEntomological Society
22: 181-202.
44 J.Entomol. Soc.Brit.Columbia 104,December2007
Newcomer,E.J. 1921.Athripsinjurytoapple.BetterFruit 16:10.
Pearsall, I.A. andJ.H. Myers. 2000a. Population dynamics ofwestern flowerthrips (Thysanoptera: Thripi-
dae)innectarineorchardsinBritishColumbia.JournalofEconomicEntomology93: 264-275.
Pearsall, I.A. andJ.H. Myers. 2000b. Evaluation ofsampling methodology fordetermining thephenology,
relative density, anddispersionofwesternflowerthrips (Thysanoptera: Thripidae) innectarine orchards.
JournalofEconomicEntomology93:494-502.
Pearsall, I.A. and J.H. Myers. 2001. Spatial and temporal patterns ofdispersal ofwestern flower thrips
(Thysanoptera: Thripidae) in nectarine orchards in British Columbia. Journal ofEconomic Entomology
94: 831-843.
Terry, L.I. 1991. Frankliniella occidentalis (Thysanoptera: Thripidae) oviposition in apple buds: role of
bloomstate,blossomphenology,andpopulationdensity. EnvironmentalEntomology20: 1568-1576.
Terry, L.I. 1997. Host selection, communication andreproductivebehaviour, pp. 65-118. In T. Lewis (ed.),
Thrips ascroppests. CAB International,NewYork,NY.
Toapanta, M., J. Funderburk, S. Webb, D. Chellemi and J. Tsai. 1996. Abundance ofFrankliniella spp.
(Thysanoptera: Thripidae)onwinterandspringhostplants. EnvironmentalEntomology25: 793-800.
Venables, E.P. 1925. Pansyspots on apple(apeculiarformofthrips injury). ProceedingsofBritishColum-
biaEntomological Society22: 9-12.