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Copyright 2005, Board of Trustees, University
y LF COAST RESEARCH AND EDUCATION CENTER
S AUG 27 1987 IFAS, UNIVERSITY OF FLORIDA
A 5007 60th Stree East
Bradenton, FL 34203
University of Florida
--- edent.on BCREC Research Report BRA1987-16 August 6, 1987
THE WESTERN FLOWER THRIPS AND THE SWEETPOTATO WHITEFLY:
NEW PESTS THREATENING FLORIDA TOMATO PRODUCTION
D. 3. Schuster and J. F. Price
Tomato production in Florida, like any other agricultural
production system, is dynamic, constantly changing and adapting
to new situations and problems. Management of pests within the
production system should also be dynamic, requiring adaptation to
new pest situations.
Two insect pests currently threaten to require changes in
pest management in Florida tomato production, the western flower
thrips (Frankliniella occidentalis (Pergande)) and the
sweetpotato whitefly (Besisia tabaci (Gennadius)). Both of
these pests are a threat, not only because of their direct attack
on plants and their resistance to insecticides, but also because
of their potential to transmit virus diseases.
* WESTERN FLOWER THRIPS
The western flower thrips was first described from specimens
collected from California in the late 1800's and was restricted
to the western half of the country. In recent years the thrips
has moved to the southeastern U.S., being first recorded in
Georgia in 1981 (Beshear 1983) and Florida in 1982 (Denmark,
personal communication). It has since been collected from the
panhandle to Miami. The western flower thrips was first
collected from tomato in the Quincy area in 1985 but has not been
collected on tomato in other production areas (Denmark, personal
communication). Populations at Quincy are currently low (Tappan,
Western flower thrips adults are minute, elongated (0.5 mm)
insects. Their wings have a feathery fringe and their bodies are
generally light yellow. Eggs are inserted into the more tender
plant tissues such as stems, buds and flower parts (Bailey 1938).
The immature stages, called nymphs, begin feeding immediately
upon hatching from the eggs. When they are full grown, they drop
to the soil where they form non-feeding, resting stages
(pre-pupae and pupae). Adults emerge to complete the life cycle.
At 85 F, the egg to adult developmental time is about 2 weeks
(Lubinkof & Foster 1977).
The western flower thrips has a host range of at least 140
plant species including numerous weeds and cultivated hosts
(Bryan & Smith 1956). Using their rasping-sucking mouthparts,
they scrape the tissue surface and suck the juices that exude.
The thrips occurs primarily in the flowers where they feed on
nectar, pollen grains, anthers, ovaries or small fruit. While
some believe that flower thrips improve pollination, populations
of about 10 per flower of a thrips (F. bispinosa (Morgan))
closely related to western flower thrips have resulted in
increased bloom drop on tomato (Schuster, unpublished data). On
grapes, feeding on developing berries results in scarring.
Oviposition on young grapes results in scars surrounded by a
light halo (Yokoyama 1977). This damage is similar to what was
observed on tomatoes in the Quincy area in 1985.
In addition to direct damage, the western flower thrips is
an efficient vector of tomato spotted wilt virus. The virus has
been documented from Jackson, Santa Rosa, Okaloosa, Jefferson,
Walton, Washington and Alachua counties on crops including
gladiolus, peanut, tomato, tobacco and watermelon (Simone 1987,
Sprenkel 1986). The disease has been recorded from at least 200
plant species around the world and has been shown to be
dessiminated by eight other thrips species besides western flower
thrips (McRitchie 1986). At least two of these, the tobacco
thrips (F. fusca (Hinds)) and the onion thrips (Thrips
tabaci Lindeman) also occur in Florida. Although the tomato
spotted wilt virus occurs in the Quincy tomato production area,
it has not yet been observed in other production areas. The
thrips which predominate in central and southern Florida are F.
bispinosa and F. cephalica (Crawford). It is not known
whether these closely related species can transmit the virus.
The symptoms of the virus vary considerably depending upon the
host plant. The foliage of infected tomato plants have thickened
veins, downward curled leaves and ring spots. Green fruit have
light green rings with raised centers and appear lumpy. Infected
plants are stunted.
Resistance of the western flower thrips to insecticides
applied for their control has often been suggested but has not
been well documented. Recent insecticide trials on a variety of
crops indicate that there are a number of insecticides registered
for use on tomato that are effective for controlling the thrips.
These include Thiodan on tomato (Oetting 1986), Monitor on cotton
(Graves et al. 1987) and Vydate, Lannate and Cygon on the
ornamental torenia (Neal et al. 1984). On lettuce, Lannate,
Guthion and Phosdrin were effective in reducing thrips numbers
but were ineffective in reducing the incidence of tomato spotted
wilt virus (Cho et al. 1986). This emphasizes the importance of
integrating insecticides with other measures for managing the
Western flower thrips-infested tomato plants in the Quincy
area in 1985 were associated with wheat plantings. Adults
apparently migrated to the tomatoes in large numbers as the wheat
ceased flowering, indicating the importance of not planting
tomatoes near or adjacent to alternative thrips hosts. Thorough
management of weeds both within and adjacent to tomato fields
should be practiced. Common beggar tick (spanish needle) is a
common weed in central and south Florida and is an excellent host
of the thrips. Reflective mulch (black plastic painted with
aluminum paint) resulted in reduced thrips numbers and tomato
spotted wilt virus incidence (Greenough 1985). Reflective
mulches have also been effective in delaying the appearance of
aphid-borne virus diseases as well (George & Kring 1971).
The sweetpotato whitefly has been noted in Florida since the
late 1800's but has only been considered a pest in the state
during the past year (Price 1987). The insect is distributed
throughout the tropical world and attacks at least 500 species of
plants including numerous weeds and cultivated vegetable,
agronomic and ornamental crops (Greathead 1986). Vegetables most
often attacked include those in the families Solanaceae
(including tomato, eggplant & pepper) and Cucurbitaceae
(including cucumber, melons & squash). The adults are small
insects about 1 mm long with pale yellow bodies and white wings.
They resemble small flies but are actually more closely related
to aphids since they have piercing-sucking mouthparts. Adults
prefer the younger leaves and deposit minute, cigar-shaped eggs
on the lower surfaces of these leaves. The eggs are attached to
the leaves with short stalks. The immature stages are usually
called nymphs and also have piercing-sucking mouthparts. The
newly hatched nymphs have well-developed legs and are the only
mobile nymphs. After finding a suitable feeding site on the
lower leaf surface, these 'crawlers' attach to feed and usually
do not move again. The subsequent three nymphal stages appear as
flattened, oval scales and are not mobile. The final immature
stage (resting or pupal stage) is more convex and elliptical and
has large, conspicuous red eyes (Lopez-Avila 1986). The
developmental time from egg to adult at 80 F on tomato is about 4
weeks (Coudriet et al. 1985). Because of the delay between the
time of egg deposition and the completion of development, the
immature stages, particularly the pupal stage, may be found on
lower, older leaves, especially on rapidly growing plants
(Ohnesorge et al 1980).
Nymphal and adult whiteflies damage plants by sucking their
sap. Chlorotic spots may appear on the upper leaf surfaces and
affected plants may become unthrifty. All whitefly stages beyond
the egg stage also produce honeydew upon which sooty mold can
grow. In addition, the sweetpotato whitefly is a known vector of
about 19 virus diseases (Brunt 1986). In 1981, an estimated $8
million in damage occurred on cantaloupe, melons and squash in
California (Duffus & Flock 1982). Estimates of yield losses of
lettuce ranged from 50 to 75 percent. Sweetpotato
whitefly-transmitted viruses affecting tomato include tomato
yellow leaf curl in the middle east and tomato yellow mosaic and
tomato golden mosaic in tropical America (Brunt 1986).
Fortunately, no viruses in Florida are known to be
transmitted by whiteflies; however, the possibility exists that
viruses presently attacking weeds could be disseminated to crop
plants or that other whitefly-vectored viruses could be imported
into Florida. The whitefly has been a serious pest in the
vegetable producing desert valleys of California when populations
have migrated from cotton, other crops and weeds (IPM Manual
Group 1985); however, no whitefly-vectored virus has been
reported on tomato there.
During the past year, the sweetpotato whitefly has been a
serious pest of ornamental greenhouse and saranhouse crops,
particularly poinsettia. A heavy field infestation was
discovered this spring on eggplant in the Boynton Beach area.
The eggplant had been double-cropped with cucumber, although the
cucumber crop had senesced by the time the whitefly infestation
was first reported. Later, a crop of chinese melon on an
adjacent farm was found to be heavily infested. Thus, both of
these infestations on field-grown vegetables may have been
associated with cucurbit crops. Active but less severe
infestations of the whitefly were found on every other vegetable
farm inspected in the vicinity including those growing tomato,
pepper, cucumber and snap beans.
Insecticides have most often been used to manage the
sweetpotato whitefly, especially on cotton. Resistance to
organophosphate and synthetic pyrethroid insecticides has been
reported in California (Prabhaker et al. 1985). The
effectiveness of selected insecticides is being evaluated at
Bradenton on poinsettia both in the laboratory using lab-reared
sweetpotato whiteflies and in the greenhouse using a naturally
occurring population. Results to date indicate that, of
insecticides currently registered for use on tomatoes, Thiodan,
Lindane, Ambush (either alone or combined with Butacide) and
Pyrenone provide very good kill of whitefly adults in the
laboratory. These same insecticides plus Monitor, Cygon and
Asana also indicated adult control in the greenhouse. Ambush,
Asana, Pyrenone and Vydate resulted in the most consistent
reductions in the numbers of nymphs surviving to adult emergence
in the greenhouse. Thus, registered insecticides are available
for the management of this pest on tomato. Reports from
greenhouse growers indicate that the effectiveness of any given
insecticide may vary from one whitefly population to another.
Growers who encounter this pest on tomato should alternate
insecticides of different chemical classes to reduce the
potential for the development of resistance. Thiodan and Lindane
are chlorinated hydrocarbons, Pyrenone is pyrethrum, Ambush and
Asana are pyrethroids, Monitor and Cygon are phosphates, and
Vydate is a carbamate. Thorough coverage of foliage,
particularly the lower, older leaves, is essential to control
nymphs and pupae.
Biological control of the sweetpotato whitefly has been
studied in many parts of the world. About 25 species of
parasites and 15 species of predators have been recorded
attacking the whitefly (Lopez-Avila 1986). Increases in whitefly
populations have been observed following the applications of
non-selective insecticides (Matthews 1986). It has been
suggested that this might occur because of the reduction in
numbers of small, wasp-like parasites which attack the immature
stages. We have recently recovered a parasite attacking
sweetpotato whitefly immatures on tomato plants in a greenhouse.
At least half of the immatures were parasitized. Although the
parasite has been observed on the whitefly on weeds in the
immediate vicinity of the greenhouse, it is hot known-whether
this parasite can survive or be effective outside a greenhouse.
There is little information available regarding the impact of
specific insecticides on parasites of the whitefly. Thus,
broad-spectrum insecticides should be used as sparingly as
possible to avoid causing whitefly populations to increase.
Cultural manipulations may aid in the management of the
sweetpotato whitefly on tomato. Since the insect can survive on
.a wide range of weed species, weeds should be thoroughly managed
both in and around fields. Tomatoes should not:be planted
adjacent to or following cucurbits since these crops may result
in greater numbers of whiteflies migrating to tthe tomatoes. As
with the western flower thrips, reflective muldtes may reduce the
numbers of invading adult sweetpotato whitefli- that alight on
Bailey, S. F. 1938. Thrips of economic importatFe in California.
Univ. Calif. Cir. 346, 77 pp.
Beshear, R. J. 1983. New records of thrips in Georgia (Thysanop-
tera, Terebrantia, Tubulifera). J. Ga. Entemol. Soc. 18:
Brunt, A. A. 1986. Transmission of diseases. Pages 43-50 In M. J.
W. Cook, ed. Benisia tabaci--a literature survey on the
cotton whitefly with an annotated bibliography. CAB Int.
Inst. Biol. Control, Silwood Park, United Kingdom.
Bryan, D. E. & R. F. Smith. 1956. The Frankliniella occidental-
is (Pergande) complex in California (Thysanoptera:Thripi-
dae). Univ. Calif. Publ. Entomol. 10: 359-410.
Cho, J. J., W. C. Mitchell & R. Mau. 1986. Development of control
procedures for tomato spotted wilt virus (TSWV) disease.
Phytopathol. 76: 1134.
Coudriet, D. L., N. Prabhaker, A. N. Kishaba & D. E. Meyerdirk.
1985. Variation in developmental rate on different hosts and
overwintering of the sweetpotato whitefly,--Benisia tab-
aci (Homoptera:Aleyrodidae). Environ. Entomol. 14:
Duffus, J. E. & R. A. Flock. 1982. Whitefly-traosmitted disease
complex of the desert southwest. Calif. Agric. 36: 4-6.
George, Jr., W. L. & J. B. Kring. 1971. Virus protection of late-
season summer squash with aluminum mulch..Conn. Agric. Exp.
Stn. Cir. No. 239.
Graves, J. B., A. M. Pavloff & S. Micinski. 1987. Large plot
evaluation of Monitor for control of western flower thrips
and two spotted spider mites, 1986. Insecticide & Acaricide
Tests. 12: 232.
Greathead, A. H. 1986. Host plants. Pages 17-25 In M. J. W. Cook,
ed. Bemisia tabaci--a literature survey on the cotton
whitefly with an annotated bibliography. CAB Int. Inst.
Biol..Control, Silwood Park, United Kingdom.
--Greenough, D. R. 1985, Aluminum-surfaced mulch and disease resis-
tance:. approaches-to the control of tomato spotted wilt
virus in solanaceous crops. M.S. thesis, La. State Univ.,
PM-Y1anu~l Group. 1985. -Integrated pest management for tomatoes,
2nd-ed. Univ. Calif., Statewide Integrated Pest Management
Proj., Div. Agric.-Nat. Resources, Publ. 3274.
.oe2-Avil-a,-A.. 1986. Natural enemies. Pages 27-35 In M. J. W.
Cook, ed..Beisia tabaci--a literature survey on the
cotton whitefly with an annotated bibliography. CAB Int.
.Inst. Biol..Control-,-Silwood Park, United Kingdom.
Lubktlrtof-, J. & D. E. -Fosteer. 1977. Development and reproductive
capacity of Frar-kLiniel a occidentalis (Thysanoptera:
-Thripidae) reared-at three different temperatures. J. Kans.
-Entomol. Soc. 50:"313-3J16. .
McRitchi-e,-J. J. 1986.-Tomato spotted wilt. Fla. Dept. Agric. &
Consumer Serv.-, Plant.Pathol. Cir. No. 287.
Neal, -Jr., J. W., P. Semeniuk & K. M. Gott. 1984. Thrips control
on torenia, 1982. "Insecticide-& Acaricide Tests. 9: 382.
Getting, R. D. 1986. rrsecti-cide efficacy against western flowers
thrips, Georgia, 1985. Insecticide & Acaricide Tests.
11: .196. .
Ohnesorge, B., N. Shara &lTT Allawi. 1980. Population studies on
the tobacco whitef-l-y Bejisia -tabaci Genn. (Homoptera:
SAleyrodidae) during the-winter season. I. The spatial dis-
tribution on some-.host: plants. Zeitschrift fur Angewandte
Entomol. 90: 226-232.
Prabhaker, N., D.. L. Ctnldriet & D. E. Meyerdirk. 1985. Insecti-
cide resistance in-the-sweetpotato whitefly, Bexisia
tabaci (Homoptera-Aleyrodidae). J. Econ. Entomol. 78:
trice, J. F. 1987. Contbtdiing a "new" pest. Greenhouse Grower.
Simone, G. W. 1987. The threat of tomato spotted wilt virus.
Univ. Fla., Inst. Food & Agric. Sci., Nematol. Entomol.
Pathol. News. 13: 5-7.
Sprenkel, R. K. 1986. Distribution of tomato spotted wilt virus
symptoms on peanut in the panhandle. Univ. Fla., Inst. Food
& Agric. Sci., IPM Newsletter. No. 22.
Yokoyama, V. Y. 1977. Frankliniella occidentalis and scars on
table grapes. Environ. Entomol. 6: 25-30.