Timing of oviposition by western flower thrips (Thysanoptera: Thripidae) in apple fruit

2007·5 MB·English

by  S D Cockfield

J.Entomol. Soc.Brit.Columbia 104,December2007 45
Timing of oviposition by western flower thrips
(Thysanoptera: Thripidae) in apple fruit
S.D. cockfield\ e.h. beers\ d.r. horton^
and E. MILICZKY^
ABSTRACT
Adult western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera:
Thripidae), were most abundant on flower clusters ofapple, Malus x domestica Bork-
hausen, fromkingbloom to full bloom. Low numbers ofthrips remained on the clusters
afterpetal fall as fruitenlarged. Thrips larvaepeakedinnumbers afterdensities ofadults
hadpeaked, usually by petal fall. Two staining procedures were developed for detecting
thrips eggs in the surface offruit ovary tissues (the edible portion offruit), and in other
blossom tissues (stamen, style, calyx, stem and leaves). Eggs were abundantin the latter
tissues throughout the bloom and post-bloom periods; the calyx appeared to be highly
preferred. Few eggs were detected in fruit ovary tissues during bloom. Egg numbers in
ovary tissues began to increase about 8-13 d after full bloom, when fruit had grown be-
mm
yond 5 diameter. The most effective timing ofpesticides corroborated the oviposi-
tion data. Formetanate hydrochloride or spinosad caused the greatest reduction in ovi-
position injury(pansy spot) when appliedfrom fullbloomto about 5 mm fruitdiameter.
Key Words: Frankliniella occidentalis, western flower thrips, pansy spot, oviposition,
apples, sampling
INTRODUCTION
Western flower thrips, Frankliniella and Proctor 1982). Damage on grapes is
occidentalis (Pergande) (Thysanoptera: identical to pansy spot of apples (Jensen
Thripidae), damages the fruit of a number 1973), and a similar pale halo surrounds
ofcrops (Childers 1997). Feeding by larvae oviposition scars on tomato (Salguero Na-
or oviposition by adult females produces vsis etal. 1991).
distinct symptoms which can occur at dif- The timing of thrips oviposition on ap-
ferent times during fruit development. ple fruit is still a matter of dispute. New-
Feeding on peach fruit afterbloom causes a comer (1921) was first to discover thrips
superficial skin blemish referred to as eggs in the center of pansy spots. He de-
'silvering'. Nectarines develop a more seri- duced that oviposition must occur "some
ous skin deformity from feeding called time during bloom", and advocated an in-
'russetting' (Childers 1997). Damage on a secticide application at pink (opening
number ofother crops is causedby oviposi- flower buds) to control the adults responsi-
tion. The disorder known as pansy spot of ble. Venables (1925) believed that oviposi-
apple, Malus x domestica Borkhausen, a tion in fruit occurred "some time between
pale halo surrounding a corky, raised scar, bloom and closing of the calyx", which
is caused by oviposition of female thrips occurs shortly after petal fall (80% of the
(Newcomer 1921). Pansy spot marks are flowers with no petals). Childs (1927) ob-
most visible on light-coloured fruit and served oviposition in fruit occurring much
result in downgraded fruit quality (Madsen later, shortly after bloom and continuing
n'aTtrceheeeF,ruWitARe9s8e8a0r1chUaSndAExtensionCenter,WashingtonStateUniversity, 1100N.WesternAvenue,We-
^USDA-ARS, 5230KonnowacPassRoad,Wapato,WA 98951 USA
46 J.Entomol. Soc.Brit.Columbia 104,December2007
mm
until fruit were about 25-38 diameter. The current control recommendation is
Madsen and coauthors (Madsen and Jack to apply insecticides either atpink (Smith et
1966, Madsen and Arrand 1971, Madsen ah 2005) orduringbloom, when adultwest-
and Proctor 1982) believed that overwinter- em flower thrips are most abundant (Terry
ing adult female F. occidentalis first lay and DeGrandi Hoffman 1988). Insecticides
eggs on sepals and flower parts, and not on (formetanate hydrochloride, spinosad, and
the edible portions of young fruit, begin- acetamiprid) used for control of thrips on
ning in early bloom. The larvae develop in apple, are moderately toxic to bees; materi-
the corolla and pupate away from the als that are highly toxic to bees are re-
flower clusters. New adults begin emerging stricted during bloom. Mitigation of toxic-
after petal fall and it is these individuals ity is accomplished by spraying either at
that lay eggs in the developing fruit. How- night or in the early morning before bees
ever, because western flower thrips pupates are actively foraging. Targeting sprays after
in soil litter, these newly emerged adults bloom would expand the choice of chemi-
would have to recolonize the apple clusters cal control tactics, and eliminate hazards to
to be responsible for the damage, and it is pollinators, providing abenefitto applepest
not yet clear that this recolonization occurs management.
to any extent. The detailed work by some The purpose of this investigation is to
recent authors (Terry and DeGrandi Hoff- assess the timing of thrips oviposition on
man 1988, Terry 1991) concluded that ovi- apple fruit in central Washington, and
position on young fruit occurs during pink evaluate insecticide timing based on this
to full bloom (80% of the flowers fully in information. We have built on the work of
bloom), although the majority of eggs de- previous authors by expanding the time
posited during those stages are laid in period and tissues in which the eggs are
flower parts, and therefore do not cause observed, as well as testing our data with
injury. insecticide timing experiments.
MATERIALS AND METHODS
Timing ofOviposition in Fruit. Densi- sealing plastic bags, stored at 5 °C and pro-
ties ofeggs, larvae, and adult thrips on ap- cessed within a week. Thrips were sepa-
ple were assessed in 2004-2006 at three rated from plant tissues by filling the bag
locations. In 2004, a block (about 2 ha) of with water, adding a few drops of liquid
'Delicious' trees at the Washington State detergent, and agitating for several seconds.
University Tree Fruit Research and Exten- Thrips and plant material were separated
sion Center (WSU-TFREC) in Wenatchee, from the soapy water by pouring through
WA, was used. No chemical thinning two nested sieves (Hubbard Scientific Co.,
sprays were used in the block. Blossom Northbrook, IL). The larger sieve (#10,
mm
clusters (n=100) or, starting at petal fall, 0.25 mesh) trapped most of the plant
king fruit (n=100) were collected at inter- material, and the finer sieve (#230, 0.0014
mm
vals corresponding to the developmental mesh) trapped the thrips (Lewis 1997).
stages ofthe apple bloom. One sample was Thrips were then rinsed into a vial of50%
taken per tree. Sample timings were early ethanol. Adults and larvae were recorded
tight cluster (flower buds unopened and separately.
touching) (2 and 6 April), pink (9 April), After the plant tissue samples were
king bloom (bloom of the first, central washed, blossom clusters were trimmed so
flower in the blossom clusters) (13 April), that only the king bloom fruitlet ovary tis-
full bloom (14 April), the start ofpetal fall sues remained, andthesewere examinedfor
(19 April), and four stages of fruit growth thrips eggs. Only eggs in this structure,
(23 April, 27 April, 4 May, and 11 May). which becomes the edible portion of the
Plant tissue samples were placed in self- fruit, cause economic damage. Direct obser-
J.Entomol. Soc. Brit.Columbia 104,December2007 47
vation of apple fruit, a method used by Apple Tissue Oviposition Studies. In
Terry (1991), was found unsatisfactory. A addition to studies of oviposition in apple
staining technique (Backus et al. 1988, fruit ovary tissues, more detailed studies
Teulon and Cameron 1995) was used in- were carried out to determine relative ovi-
stead. Trimmed fruitlets were placed in position preference in both vegetative and
McBride's stain (0.2% acid fuchsin in 95% reproductive tissues ofapple. Blossom clus-
ethanol andglacial acetic acid(1:1 vol/vol)) ters were collected from three orchards lo-
WA
for 24 h, then transferred to clearing solu- cated in Yakima County, in both 2005
tion consisting ofone part each ofdistilled and 2006. Apple varieties included were
water, 99% glycerin, and 85% lactic acid 'Delicious', 'Fuji', and 'Granny Smith'. At
(1:1:1 vol/vol/vol). This method allowed each orchard, a sample consisted of 10
samples to be stored for up to three months blossom clusters, randomly selected from
without deterioration. Samples in the clear- several trees along the orchard edge, shown
ing solution were heated in a double boiler in another study (Miliczky et al 2007) to
under a fume hood for 1 h to soften the tis- support the highest densities ofovipositing
sue. After clearing, the skin and underlying thrips. In 2005, clusters were collected at
flesh ofthe fruit was sliced off to a thick- five developmental stages: pink, king
ness of 0.5 mm, and the remaining fruit bloom, frill bloom, petal fall, and 15-25
mm
tissue discarded. The skin was placed be- fruit size. In 2006, the pink through
tween two glass microscope slides and petal fall stages were again sampled, but
pressed flat. The thin tissue was observed two post-petal fall samples were taken: 10
mm mm
under a dissecting microscope using transil- fruit size and25 fruit size. Clusters
luminationto reveal the darkereggs. were placed in self-sealing plastic bags, and
The timing of egg deposition was ftir- transportedto the laboratoryon ice.
ther studied in 2005 in a commercial or- A modified egg staining procedure was
chard block (2 ha) of 'Braebum' apples used for these studies. Blossom samples
nearthe town ofOmak, WA, and in 2006 in were immersed in a warm (60 °C) solution
a commercial orchard block (4 ha) of of white vinegar (Heinz Distilled White
'Cameo' apples in Bridgeport, WA. Flower Vinegar, H.J. Heinz, Pittsburgh, PA) and
clusters and king fruit were sampled as de- blue food colouring (McCormick Blue
scribed previously, including sample sizes. Food Coloring, Hunt Valley, MD), using
In 2005, samples were taken at tight cluster six drops of food colouring in 40 ml of
(16 April), pink (20 April), king bloom (24 vinegar. Samples were left in the solution
April), full bloom (28 April), petal fall (1 for 20 min, after which the tissues were
May), and five stages offruit growth (4, 8, removed from the solution and blotted dry.
11 16 and 23 May). In 2006 samples were The vinegar caused tissue layers to sepa-
taken at pink (24 April), king bloom (28 rate, exposing the eggs, while the blue food
May), full bloom (4 May), the end ofpetal colouring stained the oviposition scar and
fall (12 May), and four stages of fruit egg. Samples were examined under a dis-
growth (16 and 24 May, 2 and 9 June). The sectingmicroscopeto assess eggnumbers.
larger range offruit sizes collected in 2006 Egg numbers on each ofthe five struc-
necessitated slightly modified handling. tures were determined: flower reproductive
mm
Smaller fruit (<15 diameter) were organs (stamen, style), flower calyx, stem
stained and examined as described previ- below flower or fruitlet, leaves, or fruitlet
ously. Larger fruit (>15 mm) were stained ovary tissues. For each blossom cluster, we
only, without clearing or dissection. Be- counted total number ofleaves and flowers
cause the skin ofthe larger fruit was almost in the cluster, and then randomly selected a
free of trichomes, the punctures and pink- subsample ofthree flowers and three leaves
stained eggs were clearly visible using light of each cluster for examination. Once egg
microscopy. In a few rare cases, oviposition numbers had been determined for each of
sites were excisedforcloserexamination. the five structures within this subsample.
48 J.Entomol. Soc.Brit.Columbia 104,December2007
we used these estimates ofdensity in com- analysis of variance for a completely ran-
binationwithourcounts ofleaves and flow- domized design (Statistical Analysis Insti-
ers in the cluster to obtain by extrapolation tute 1988). Treatment means were sepa-
an estimate ofegg numbers for each ofthe rated with a Least Significant Difference
five structures in the entire blossom cluster. test, a=0.05.
Percentage distribution of eggs among the 2006 Insecticide Timing Trial. This
five structures was then determined using experiment was conducted in the same
these extrapolated estimates of egg densi- commercial orchard block used for the
ties. Samples from the three orchards were 2006 oviposition study. The orchard (4 ha)
pooled. was bordered on three sides by native vege-
2004 Insecticide Timing Trial. This tation. The 8-year-old 'Cameo' trees were
m
trial was conducted atthe same site used for pruned to a trellis about 3 high. Tree
the 2004 oviposition study. Insecticides spacing was 0.9 x 3.7 m. The experiment
were used to kill adult thrips in blossom was a randomized complete block design
clusters at different stages of blossom or with blocks determined by proximity to the
fruit development. One hundred 'Delicious' native vegetation. Four replicated plots (15
apple trees were selectedrandomly, and one trees in a single row) were sprayed with
branch with 7-10 flower clusters was se- either formetanate hydrochloride or spino-
lected on each tree. Adult thrips were al- sad (Success® 2SC, Dow AgroSciences,
lowed to migrate back to the branches, thus Indianapolis, IN) using an airblast orchard
treatments created periods ofreduced adult sprayer (Rears Pak-Blast, Rears Mfg,
presence. The experiment was a completely Eugene, OR) calibrated to deliver 1,871
randomized design with 10 treatments litres/ha. Plots were separated by five un-
(spray timings) and 10 replicates treated rows. Application timings ranged
mm
(branches). Thrips were killed by spraying fi-om king bloom through 27 fruit size
the branches to drip with a solution of for- (Table 2), plus an untreated check. The first
metanate hydrochloride (Carzol® 92SP, three sprays were applied at night to avoid
Gowan Co., Yuma, AZ) at 27.6 g Al/lOO contact with pollinators. All other sprays
litres. Material was mixed in a yi-litre spray were appliedduringthe day.
bottle. Applications were made at one of Between 110 and 150 fruit perplot were
nine stages from tight cluster through about examined for pansy spot under a micro-
16 mm fruit diameter (Table 1). One group scope on 6 June. The proportion (p) offruit
of 10 branches was sprayed on all nine with pansy spot was transformed with arc-
dates to eliminate thrips during the entire sine [square root (p)]. Data were analyzed
bloom and early fruit growth period. Fruit with two-way ANOVA for two insecticide
were harvested from each treatment on 24- treatments and six application timings.
25 May. The proportion (p) offruit injured Main effects means for insecticide or spray
by thrips was transformed by arcsine timing were separated with a Least Signifi-
[square root (/?)], then analyzed using cant Difference test.
RESULTS AND DISCUSSION
Timing of Oviposition in Fruit. The in the samples during the post petal-fall
abundance ofadult thrips on apple blossom period in 2004 and 2006. Adults were still
mm
clusters increased as appleblossoms opened recovered on the 17.3 diameter fruit
(Fig. 1). Abundance in blossoms was high- sample date in 2006, 24 d after full bloom.
est at king bloom. From petal fall onwards, Larvae, which could not be identified to
king fruitwere sampledratherthanblossom species, peaked afteradults, usually on king
clusters. Adults were most abundant on fhiit after petal fall (Fig. 1). Contrary to
king fruit atthe beginning ofpetal fall, then expectation, the peak abundance ofeggs in
decreased rapidly. Low numbers remained fruit was later than the peak in larvae, with
J.Entomol. Soc.Brit.Columbia 104,December2007 49
o
(/)
0)
1/)
_3
O
E
o
(/)
<oo
m
o
o
CL
27-Mar 10-Apr 24-Apr OS-May 22-May 05-Jun 19-Jun
Figure 1. Densities ofthrips eggs inking fruitovarytissues, andadultand larval stages onblos-
som clusters (tight cluster to full bloom) and king fruit (petal fall and later). Adult thrips (A);
larvae (); eggs (•).
a relatively long lag period between peak This is substantially later than is reported
abundance of adults in flow^er clusters and by some authors (Newcomer 1921,
eggs in the fruit ovary tissues. This result Venables 1925, Terry 1991), but in general
suggests that females deposited eggs exten- agreement with others (Childs 1927,
sively in other, unsampled plant structures Madsen and Jack 1966). Stained eggs were
mm
within the blossom clusters (see Apple Tis- detected in oviposition scars after 25 in
sue Oviposition Studies). 2006 but were no longer found in scars in
mm
Relatively fewthrips eggs were found in finit that were 31.7 diameter in early
fruit during the period most often targeted June, which agrees with the observations of
for sprays (Fig. 2), viz., pink through petal Childs (1927).
fall, although this is the period when adults Apple Tissue Oviposition Studies. The
were most abundant (Fig. 1). The greatest calyx and stem received between 72 and
increase in egg numbers deposited in fruit 98% ofthe eggs deposited in sampled blos-
occurred after the start of petal fall, be- som clusters, depending upon blossom
tween 5.6 - 9.0, 6.0 - 11.6, and 5.7 - 12.5 stage (Fig. 3). By the time fruit reached
mm mm
diameterin the three years ofthe study. approximately 10 in size, they had be-
This corresponded with 13 - 20, 13 - 18, come moderately attractive as oviposition
and 8 - 16 d after full bloom, respectively. sites. Eggs in fruit ovary tissues never ex-
50 J.Entomol.Soc.Brit.Columbia 104,December2007
o
o
LU
27-Mar 10-Apr 24-Apr 08-May 22-May 05-Jun 19-Jun
Figure2. Thrips eggdensities inking fruit ovary tissues (•) andkingfruitsize
ceeded 13% ofthe total eggs found at any andMayer 1994).
blossom stage. Some oviposition also oc- 2004 Insecticide Timing Trial. The
curred in leaves and floral reproductive timing of formetanate hydrochloride appli-
parts (stamens and styles), but this com- cations affected the percentage of fruit
prisedasmall proportion ofthe total eggs. damaged {F= 4.45; df= 9,96; P < 0.0001).
This study provides insight into several Applications were most effective in reduc-
issues regarding thrips damage to apple. In ing pansy spot during the period from the
mm
the fruit oviposition timing studies, where start ofpetal fall to 5.6 fruit; applica-
only eggs laid in fruit ovary tissues were tions before or after this timing were less
assessed, the larvae appeared to be out of effective (Table 1). An application at king
sequence with the eggs (Fig. 1). The larvae bloom, for example, was clearly too early.
may have been hatching from eggs laid in The optimum timing was, as would be ex-
structures not monitored during that study. pected,just before the peak oviposition that
The second issue deals with predicting the occurred some time between 5.6 and 10.9
mm
amount of fruit damage from adult density fruit size (Fig. 2). The results indicated
estimates. The high percentage ofeggs be- that prevention of the oviposition surge at
ing laid in non-fruit tissues may be respon- the end ofpetal fall was key for pest man-
sible for the overall poor correlation be- agement, but that the entire period of ovi-
tween densities of adult flower thrips and position was not of interest. In fact, one
fruit damage in apples (Terry 1991, Bradley well-timed spray at petal fall was equiva-
J.Entomol. Soc. Brit.Columbia 104,December2007 51
100 2005
Stamen,
80
style
60 FiT^m Stem
Leaves
I I
40 Fruitlet
ovary
tissues
S) 20
0
O
0)
B
c
<u
i 100
CL
80
Figure 3. Percentage ofeggs depositedin various flowerand fruitparts as afunction ofblossom
andfruit stage (2005-06). Numbers inparentheses aretotal eggs countedin the subsamples.
lent to multiple applications made over the check (data for check plots not shown).
39-d period when adults were present in Thus, insecticides applied at king bloom or
blossomclusters. at any interval after the fruit had attained a
mm
2006 Insecticide Timing Trial. Fruit diameterof5.7 provided no benefit.
damage was affected by timing of spray In summary, data reported here support
application (F = 5.74; df = 5,36; P = arevision ofthe recommended spray timing
0.0005), but not by the type of insecticide for managing western flower thrips in cen-
used (F = 0.05; df = 1,36; P = 0.83). The tral Washington apple orchards. The current
interaction term was not significant (F = recommendation that insecticides should be
0.34, df = 5,36; P = 0.89), thus the main applied atpink(Smith etal. 2005) is clearly
effects means are ofmost interest (Table 2). too early forpreventing damage, although it
Fruit injury on trees treated at full bloom or may reduce adult thrips populations. There
mm
the end ofpetal fall (5.7 diameter king is an optimal spraywindow from full bloom
mm
fruit) was significantly lower than injury on to 5 fruit diameter, similar to that de-
trees treated at all other times (Table 2). scribed by Madsen and Jack (1966) for
Meanpercentage offruitwithpansy spoton British Columbia, Canada, but later than
trees treated at kingbloom orany time after that described by Terry (1991) for Arizona,
mm
5.7 diameter king fruit varied between USA. The period of optimal timing ex-
3.1 and 3.8% (Table 2), compared to a tended from 8 - 13 d in 2004 - 2006, giving
mean damage of 2.6% in the unsprayed some flexibility in orchard operations. The
52 J.Entomol. Soc.Brit.Columbia 104,December2007
Table 1.
Mean percentage offruit (SEM) with pansy spot from apple tree branches treated
with formetanatehydrochloride on differentblossomorfruitgrowth stages, 2004
%
Stagetreated Application date damage'
1igniclusier J /\prii 1 1 /I /"I (WckU
rinK y/\.prii on 1 (A A\rx
Kingbloom IJ April lU.j \5./jabc
Fullbloom 16 April 7.0 (2.5)bcd
mm
Petal fall, 2.7 (0.15) 20 April 2.5 (1.7)cde
mm
Petal fall, 2.9 (0.18) 23 April 1.7 (1.7)de
mm
Petal fall, 5.6 (0.31) 27 April 0.0 (O.O)e
10.9 (0.78) mm 4 May 12.5 (4.3)ab
15.8 (0.61) mm 11 May 11.8 (4.7)abc
All stages All dates 0.0 (O.O)e
'Means followed by the same letter are not significantly different, Least Signifi-
cantDifference test, a=0.05.
Table 2.
Mean percentage offruit (SEM) with pansy spot from apple trees treatedwith either formetan-
atehydrochloride orspinosadon differentblossomorfruitgrowth stages, 2006'
Formetanate HCl Spinosad
Stage treated Applicationdate Pooledmeans
(1 kgAl/ha) (0.14kgAl/ha)
Kingbloom 28 April 3.5(1.8) 2.8 (1.4) 3.1 (l.l)a
Fullbloom 4May 0.5(0.3) 0.7 (0.5) 0.6 (0.3)b
Petal fall, 5.7 mm 12 May 0.6(0.4) 1.0 (0.2) 0.8 (0.2)b
12.8 mm 17 May 4.1(1.9) 3.3 (0.9) 3.7 (l.O)a
17.3 mm 25 May 4.2(1.1) 3.4 (0.9) 3.8 (0.7)a
mm
26.7 1 June 3.4(0.7) 3.1 (1.2) 3.3 (0.6)a
Pooledmeans 2.7(0.5)a 2.4 (0.4)a
' Means within columns (dates) or between columns (insecticide) followed by the same letter
arenotsignificantly different. Least SignificantDifference test, a=0.05.
beginning of this period (full bloom) coin- would be after bee hives had been removed
cides with the timing of blossom thinning fi-om the orchard, would minimize damage
sprays, suggesting the possibility of com- potential to bees and eliminate the need to
bining materials. The latterpart ofthe spray apply insecticides in the late evening or at
window coincides with early fruit thinning night. The latter timing also opens up the
sprays that are applied at 80% petal fall, or potential use ofmaterials that are effective
mm
3-5 fruit diameter (Smith et al. 2005). on thrips, but could not otherwise be used
A petal-fall or post-petal-fall spray, which because ofbee hazard.
J.Entomol.Soc.Brit.Columbia 104,December2007 53
ACKNOWLEDGEMENTS
We thank R. Talley, A. Schaub, T. and N. Stephens ofColumbia IPM for their
Houghland, Aaron Galbraith, Amy cooperation. This work was supported in
Blauman, and Merilee Bayer for assistance part by grants from the Washington Tree
in the field and laboratory, personnel of FruitResearch Commission.
LeSage Orchards and Arrowhead Ranch,
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