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Whiteflies cause problems for southern California growers

Authors:
Whiteflies cause problems for
southern California growers
Marshall
W.
Johnson
0
Nick
C.
Toscano
0
Harold T. Reynolds
Edward
S.
Sylvester Ken Kid0 Eric T. Natwick
A
task
force of scientists
is
searching
for effective whitefly controls.
During
1981,
unusually high whitefly
populations on cotton and vegetable crops
began causing multiple problems in the desert
areas of southern California and western
Arizona. The problems included direct plant
injury by whitefly feeding, reduced quality of
produce and fiber because of honeydew accu-
mulation, and lower crop yields as
a
result of
virus or viruslike diseases carried by the
whiteflies. Total estimated economic damage
ranged in the millions of dollars: cotton,
su-
garbeets, squash, melons, and iceberg lettuce
were the most seriously injured crops.
Several species of whiteflies are present in
California’s Imperial and Coachella valleys.
Among these are the sweetpotato whitefly
(also known as the cotton and tobacco
whitefly),
Bemisia tabaci
(Gennadius);
banded-wing whitefly,
Trialeurodes abu-
tilonea
(Haldeman); and iris whitefly,
Aleyrodes spiraeoides
Quaintance. The
banded-wing whitefly is predominantly
found in cotton from early spring to July. In
July, populations of the sweetpotato whitefly
surpass those of the banded-wing whitefly.
The iris whitefly is rarely found and is not a
problem on agricultural crops.
Whiteflies are generally found in the trop-
ics and subtropics, roughly corresponding to
the area between the 30th parallels. In the
tropics they occupy the general ecological
niche held by aphids in temperate areas.
Sweetpotato whitefly has been reported in
parts
of
Africa, southern Europe, the Middle
East, India, Sumatra, Formosa, Brazil, and
the southwestern United States. The banded-
wing whitefly is found in 33 of the
50
United
States, parts
of
Mexico, and the West Indies.
Biology
Whiteflies are small plant-sucking insects
(1
to
3
mm) found on leaf undersurfaces.
They are not true flies, but belong to the
order Homoptera, which includes aphids,
scale insects, and psyllids.
Eggs are deposited on the undersides
of
leaves and in
5
to
12
days, during the summer,
hatch into the crawler stage. The six-legged
crawler moves about until it finds a suitable
feeding site, usually on the leaf undersurface.
Once the crawler inserts its mouthparts (sty-
lets) to feed, it remains at the site until the
adult stage. The stylets usually penetrate
between the epidermal and parenchyma cells
of
the leaf to the phloem (path of sugar and
nutrient movement).
After feeding begins, the crawler molts and
appears scalelike. It continues to feed and
passes through two more molts. After the
third molt, the whitefly pupates and stops
feeding until emergence as an adult.
During the summer, the whitefly develops
from egg to adult within
16
to 35 days, de-
pending on the temperature. After emerging
from the pupa, adult whiteflies mate, and the
females begin to deposit their eggs. Eggs
from unmated females produce males only.
The female lays approximately 300 eggs in
her lifetime. Whiteflies can fly only for short
distances, but winds disperse them several
miles because
of
their minute size.
Both
of
the major whitefly pests in the
southern California desert have a wide host
plant range. The sweetpotato whitefly report-
edly feeds on
as
many as
56
plant species
worldwide. In the Imperial and Coachella
valleys, cultivated host plants include cotton,
lettuce, squash, cucumbers, and melons,
although the whitefly is not known to re-
produce on lettuce in the field. Wild hosts
include bindweed
(Lantana
spp.), prickly let-
tuce
(Lactuca serriola),
and
Malvaparvrfora
L. The banded-wing whitefly has a larger
worldwide host range
of
approximately 140
plant species, several
of
which grow in south-
ern California.
Crop
damage
Whiteflies may injure a crop in a variety of
ways. High populations feeding on nutrients
may affect the plant’s physiological process-
es, ultimately causing leaf shedding and a
reduced growth rate in some crops. Chlorotic
spots appear at feeding sites on leaf surfaces.
Vast amounts
of
honeydew produced by
larvae may discolor leaves. In cotton, honey-
dew falling onto lint in open bolls frequently
supports the growth of sooty molds
(Alter-
naria
spp.). When abundant in the lint, the
sticky excretion interferes with picking and
ginning. Honeydew Contamination results in
lower quality fiber that is difficult to spin and
thus reduces its market value.
The ability to spread virus
or
viruslike
plant diseases makes high whitefly popula-
tions a menace to southern California melon,
lettuce, and cotton. Larvae and adults pick
up virus particles when they feed on infected
24
CALIFORNIA AGRICULTURE, SEPTEMBER-OCTOBER
1982
B
Jack Kelly Clark
A
Jack Kelly Clark
C
The
sweetpotato whitefly
(A)
feeds on
56
plant species, including
cotton, lettuce, and melon.
It
caused major damage
in
southern
California
in
1981.
The
banded-wing
whitefly
(B)
has a host range
of
140
species.
A
tiny
wasp,
Encarsia
formosa,
(C)
is
an effective
natural enemy of the
whitefly
in
desert areas.
plants. Adults moving and subsequently
feeding on susceptible healthy plants spread
the disease. Acquisition
of
a pathogen from
a
diseased host plant may take from
a
few min-
utes to several hours, depending on the path-
ogen and whitefly species. Usually, the
pathogen may be transmitted over a long dis-
tance and period of time, once it has been ac-
quired by a whitefly adult.
The major diseases thought to be spread by
whiteflies in the desert areas are cotton leaf
crumple, infectious yellows, and cucurbit leaf
curl. Several less prominent diseases have
also appeared on many vegetable crops.
Unfortunately, the viruslike pathogen
or
pathogens responsible
for
the three most im-
portant diseases have not been positively
identified, although several plant pathology
laboratories are investigating the problem.
Some infested melon crops suffered almost
total yield losses in the 1981-82 growing sea-
son. Of the three diseases, infectious yellows
had the most impact, reducing early-season
lettuce production as much as
50
percent.
Population increase
The increased whitefly populations and
subsequent spread
of
viruslike plant diseases
in southern California were probably pro-
duced by several simultaneously occurring
factors. Examination
of
the typical popula-
tion cycle of the sweetpotato whitefly in the
Imperial and Coachella valleys may provide
insight. Basically, whiteflies undergo similar
population cycles annually, although large
differences in their peak density levels may
occur among individual years. The whiteflies
overwinter on wild plants such as
Malva
spp.
and on available volunteer and stub cotton
(regrowth from cut stalks). Stub cotton is not
Max Badgley
permitted in California, but is found in Ari-
zona. Low winter temperatures inhibit rapid
whitefly development. During May, after the
spring cotton crop has germinated, whitefly
adults move onto young cotton seedlings that
have developed their first true leaves.
Unusually warm winters without “killing
frosts” experienced in previous years may
have allowed large numbers of whiteflies to
overwinter, producing abnormally high pop-
ulations in the spring. Higher initial spring
populations may have springboarded from
cotton onto susceptible vegetable crops. The
presence of cotton not destroyed after har-
vest, along with wild host plants harboring
disease pathogens, may have been respon-
sible for the unexpected epidemic of plant
diseases spread by the high numbers
of
whiteflies.
Whiteflies develop fastest during August
CALIFORNIA AGRICULTURE, SEPTEMBER-OCTOBER
1982
25
and September when daytime desert temper-
atures are greater than
100°
F.
Whitefly pop-
ulation growth, normally checked by natural
enemies, was rapid, apparently because
pyrethroid-based insecticides used in the area
reduced parasite numbers. Records from
1975
to
1981
show an increase in whitefly den-
sities in Imperial Valley experimental cotton
plots with the more frequent use
of
pyre-
throids to control the tobacco budworm,
Heliothis virescens
(F.), and the pink boll-
worm,
Pectinophora gossypiella
(Saunders).
Similar outbreaks were reported in Thailand
and Sudan in
1980
and
1981,
respectively,
when pyrethroids were used to treat cotton
pests.
After whitefly densities peak in August or
September, they decline to
a
relatively low,
stable density until the cotton is harvested or
cotton leaves are killed by frost. At this time,
winter vegetable crops and wild plants be-
come important overwintering hosts. After
vegetable crops are harvested, whiteflies and
disease pathogens survive on perennial wild
hosts.
Control
Conventional pesticide applications do not
control whiteflies on cotton. Insecticides may
reduce large adult whitefly populations but
usually do not affect immatures. The long
egg incubation period allows crawlers to
emerge long after insecticides have reduced
adult populations. The immobile larval and
pupal stages have a waxy covering, which
generally protects them from insecticides.
Materials that kill whitefly immatures cannot
be applied effectively by air because of poor
pesticide delivery to leaf undersurfaces.
Fortunately, whiteflies in desert areas have
several effective natural enemies, such as the
tiny parasitic wasps
Encarsia formosa
Gahan
and
Eretmocerus haldemani
Howard. Adult
female wasps deposit their eggs in the bodies
of whitefly larvae and pupae, and parasite
larvae feed on the body fluids of the imma-
ture whiteflies.
Encarsia formosa
requires
15
days to develop from egg to adult at
75O
F.
The female parasite lays up to
32
eggs during
her lifetime. The immature form
of
Erermo-
cerus haldemani
feeds only on the pupal stage
of
the whitefly and takes
22
days to develop
from egg to adult at
75O
F. The value
of
the
whiteflies' natural enemies has been demon-
strated many times
in
various parts
of
the
world. When insecticides such
as
DDT were
applied to control other pests, whitefly para-
sites were reduced, and whiteflies increased.
Until the major factors contributing to the
increase
in
whiteflies and disease spread can
be established, no tested preventive or con-
-
5
4-
0
c
.-
r
!%
3-
z
2-
1-
64
t
m
Sweetpotato whitefly
D
Banded-wing
whitefly
Use
of
synthetic
pyrethro 'egun
'64 '65
'66
'67 '68 '69 '70 '71 '72 '73 '74
I
5
'76
'I
...
'78
d
'79
'80
Survey date
(1964-81)
Populations of sweetpotato
whitefly
have ballooned
in
imperial
Valley
cotton.
trol measures can be recommended. How-
ever, some guidelines exist for decreasing
potential whitefly problems. To reduce
sources
of
disease, destruction
of
all
stub cot-
ton and management
of
weed hosts along
roadsides, ditchbanks, and fencerows, and in
production acreage is advisable. To conserve
natural enemies
of
whitefly, insecticidal con-
trol
of
budworm and pink bollworm in cot-
ton fields with potential whitefly problems
should be conducted with pyrethroids only
when absolutely necessary. Immediately after
harvest, plant stands should be destroyed to
prevent regrowth and the production
of
weeds that could harbor diseases. Cotton
should be terminated early. Lettuce or cucur-
bit crops should be planted away from ma-
ture or obviously disease-infected crops to
reduce chances
of
virus infection by naturally
dispersing whiteflies.
Researchers at the University
of
Califor-
nia, University
of
Arizona, and the
U.S.
Department
of
Agriculture (USDA) are
studying the whitefly problem. A whitefly
task force
of
17
University of California and
USDA scientists has proposed several re-
search objectives to determine the causes
of
and solution to this problem. Plant patholo-
gists are attempting to isolate and characterize
the causal agent(s)
of
whitefly-transmitted
diseases in cucurbit and lettuce crops and
to develop serological methods for rapid
detection
of
the agents. Lettuce and squash
varieties and the "world's collection"
of
muskmelon varieties are being screened for
resistance to whitefly and disease pathogens.
In-depth studies
of
whitefly biology and pop-
ulation dynamics may reveal weak links in the
insect's life cycle that can be exploited to con-
trol the pest. Investigations into biological
and chemical controls
of
whiteflies and their
interactions on cotton and lettuce may pro-
duce more efficient management practices.
Field reports indicate that overwintering
whitefly population densities are quite low. It
is hoped that the whitefly problem in the
1982-83
growing season will be minimal. For-
tunately, growers facing the upcoming season
will be better prepared to face the whitefly
threat if it materializes.
Marshall
W.
Johnson
is Post-graduate Research
Assistant, Department of Entomology, Nick C.
Toscano
is
Pest Management Program Director.
Cooperative Extension, and Harold
i?
Reynolds
is
Professor of Entomology, all at University of Cal-
ifornia, Riverside; Edward
S.
Sylvester is Professor
of Entomology, U.C., Berkeley; Ken Kid0
is
Stoff
Research Associate, Cooperative Extension,
U.
C.,
Riverside; and Eric
i?
Natwick is Farm Advisor,
Cooperative Extension, Imperial County.
26
CALIFORNIA AGRICULTURE, SEPTEMBER-OCTOBER
1982
... The total value of cotton dropped approximately $174,009,389 and the pesticides costs raised to $264.39/ha. Meanwhile the whitefly populations in the cotton fields also rise to an exponential level resulting in appearance of several disease symptoms and yield losses (Johnson et al., 1982). The year prior to Bt cotton introduction (1995), at a cost of $373 million and nearly two thirds of cotton crop cultivated land in the United States was treated with insecticides to control cotton pink bollworms (Williams, 1996). ...
... Similarly, the non-stop use of pyrethroids for the management of tobacco budworm and crimson bollworm in south California led to growth in populace of whitefly (Johnson et al. 1982). The growth in populace of whitefly in Egypt, Sudan, Syria, Thailand, Israel, Zimbabwe, China, Pakistan and India is because of the extended use of artificial pyrethroids. ...
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... Among them, the Middle East-Asia Minor 1 (MEAM1) and Mediterranean 1 are considered to be the most widely distributed species worldwide, causing substantial economic damage to crops (Xu et al., 2011;Liu et al., 2012). B. tabaci has a wide host range with a total of 600 different plant species from different families such as: Compositae, Cruciferae, Cucurbitaceae, Euphorbiaceae, Leguminosae, Lamiaceae, Malvaceae, and Solanaceae (Mound and Halsey, 1978;Johnson et al., 1982;Elsey and Farnham, 1994;Bayhan et al., 2006;Li et al., 2011). In spite of the large-scale of host-plant use, whiteflies show diverse behavior concerning to host plant preference, oviposition, ecological adaptation as well as population size and degree of plant damage (Butler and Henneberry, 1989;Costa et al., 1991). ...
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Whiteflies are Hemipterans that typically feed on the undersides of plant leaves. They cause severe damage by direct feeding as well as transmitting plant viruses to a wide range of plants. However, it remains largely unknown which genes play a key role in development and host selection. In this study, weighted gene co-expression network analysis was applied to construct gene co-expression networks in whitefly. Nineteen gene co-expression modules were detected from 15560 expressed genes of whitefly. Combined with the transcriptome data of salivary glands and midgut, we identified three gene co-expression modules related to host plant selection. These three modules contain genes related to host-plant recognition, such as detoxification genes, chemosensory genes and some salivary gland-associated genes. Results of Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses elucidated the following pathways involved in these modules: lysosome, metabolic and detoxification pathways. The modules related to the development contain two co-expression modules; moreover, the genes were annotated to the development of chitin-based cuticle. This analysis provides a basis for future functional analysis of genes involved in host-plant recognition.
... Bemisia tabaci is a thermophilic insect (Avidov 1956) and it is evident from the present study that this pest is well adapted to cotton-agroecosystem, to build-up its population faster during the summers. Being polyphagous, B. tabaci remains active in low or high numbers around the year on other crops or weed host plants (Hussain and Trehan 1933;Hussain et al. 1936;Butler Jr et al. 1986;Johnson et al. 1982;Melamed-Madjar et al. 1979;Gerling 1984;Gerling 1996). Our studies indicate that it shifts to cotton seedlings immediately after the cotton emergence during mid-May and establishes itself by the end of June on the upper leaves of the plant. ...
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Bemisia tabaci is the most destructive insect of cotton worldwide. We analysed infestation dynamics of B. tabaci in cotton during summers of 2015–2017, and predicted the factors influencing its abundance. The incidence of B. tabaci on cotton was exceptionally high in 2015 (25.91 ± 2.14 adults/3 leaves) as compared to 2016 (9.53 ± 1.23 adults/3 leaves) and 2017 (8.54 ± 1.12 adults/3 leaves). Minimum temperature, maximum-minimum relative humidity and rainfall influencing the B. tabaci population build-up were predicted using PCRA technique with reasonable accuracy (R2 = 0.87). The results also showed that monitoring/ sampling of B. tabaci in cotton should be done before 10:00 h. Among different cotton cultivars, Ankur 3028 and Bioseed 6588 were most susceptible to B. tabaci infestation. Bemisia tabaci incidence in cotton interferes with the secondary metabolite production in different cultivars. Pesticides tested for management of B. tabaci gave a maximum population reduction ranging from 42.91 to 77.01% 7 days after spray. The efficacy of tested pesticides persisted up to 10 days after spray. Maximum control of B. tabaci was achieved by flonicamid > clothianidin > diafenthiuron > dinotefuran > thiamethoxam, whereas, ethion was found least effective. Pyriproxyfen have nymphicidal action and provided maximum reduction (68.62%) in whitefly population after 10 days of spray.
... Brinjal, potato and tomato play major role in its carryover to cotton. Butler et al. (1986) observed that the winter crops and vegetables act as major source of carryover to summer crops especially from the U.S.A. Similar observations on these hosts in the carryover are available- Johnson et al. (1982) from Southern California, Melamed-Madjar et al. (1979) and Gerling (1984) from Israel, Nachapong and Mabbit (1979) and Mabbit (1978) from Thailand and Mohyuddin et al. (1989) from Pakistan. ...
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... The repeated use of synthetic pyrethroids, cypermethrin and deltamethrin against bollworms on cotton in Thailand caused the resurgence of whitefly, Bemisia tabaci (Gennadius) (Wanghoonkong 1981). Similarly, the continuous use of pyrethroids for the control of tobacco budworm and pink bollworm in south California resulted in increase in population of whitefly (Johnson et al. 1982). The increase in population of whitefly in Egypt, Sudan, Syria, Thailand, Israel, Zimbabwe, China, Pakistan and India is due to the increased use of synthetic pyrethroids. ...
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This study was conducted to evaluate the efficacy of some neonicotinoid insecticides including , Actara 25 WDG (foliar and soil treatment), Confidor 200 SL, Calypso 480 SC, Polo, Confidor 5 G against cotton whitefly Bemisia tabaci on Eggplant (Solanum melongena L.) during the growing season of 2018. The results revealed that the highest population of the adults was concentrated on the upper leaves at the new growth of the plant, while the majority of nymphs were found on the middle leaves of the plant, and the females preferred to lay the eggs on the upper leaves because the highest proportion of eggs was found on the upper leaves. The foliar application of Actara and confidor were significantly effective against the whiteflies after one day of treatment. While the soil treatments of the Actara and Confidor showed the least efficiency at one day after the treatment; all treatments except Polo were significantly superior over control in decreasing the population of the nymphs at the day 14 after the treatment. Polo did not show any efficiency in the reduction of the number of live nymphs. The data on efficacy of the tested neonicotinoid insecticides against the B. tabaci on the eggplant under the greenhouse showed different efficiency according to the treatment method. At one day after the application, foliar spraying of Actara and Calypso were the most efficient; and the efficacy of all tested insecticides increased up to the day 14 after application, and foliar treatment of Actara gave the highest efficacy after 14 days
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