An Assessment of the Biology and Management
Strategies of Bemisia spp. from an International Perspective
Validation, Refinement and Implementation
of Sampling Plans for Bemisia tabaci in Cotton
Spatial and Temporal Distribution of
Fourth-Instar Larvae of Trialeurodes vaporariorum and Bemisia
tabaci in Tomato Plants
Spatial and spatio-temporal distribution
of both species was similar within the leaflets. 'Mus, there was
no niche differentiation as a function of the spatial distribution
of these specie'
A New Approach to Assessment of the Honeydew
Content of a Cotton Crop
Introduction of an Exotic Whitefly (Bemisia)
Vector Facilitates Secondary Spread of Jatropha Mosaic Virus, a
Geminivirus Previously Vectored Exclusively by the Jatropha Biotype
The Capsid Protein - A Determinant of
Host Plant Affiliations of Whitefly-Transmitted Geminiviruses?
Predacious Arthropods of Bemisia tabaci
on Tomatoes in Florida
The Use of Macrolophus caliginosus as
a Whitefly Predator in Protected Crops
The application of M. caliginosus
is discussed and results in tomato, eggplant, cucumber and gerbera
are presented release of Exotic Natural Enemies of Bemisia tabaci
in the United States
Foreign Exploration for Natural Enemies
of Bemisia tabaci s.L.
Predators and Parasitoids as Biological
Control Agents of Bemisia in Greenhouses
Parasitoids of Bemisia tabaci in
Cotton in Santiago del Estero, Northwestern Argentina
Parasitoids of Whiteflies: Their Potential
as Controlling Agents of Outdoor Populations of Bemisia spp.
Biological Control of Bemisia tabaci
with Encarsia formosa: A Realistic Option?
Development of Augmentative Biological
Control of Bemisia argentifolii on Field and Greenhouse Crops
Systematics of Eretmocerus (Hymenoptera:
Aphelinidae), an Important Parasite of Bemisia
Host Killing and Time Allocation of the
Parasitoid Encarsia transvena
Potential for Biological Control of Mixed
Trialeurodes vaporariorum and Bemisia tabaci Populations
in Winter Tomato Crops Grown in greenhouses
Efficacy of the Fungus Aschersonia
aleyrodis and the Coccinellid Predator Delphastus pusillus,
Used to Control Bemisia tabaci in Greenhouse Cucumber
Global Distribution of Naturally Occurring
Fungi of Bemisia tabaci s.L. and Their Potential as Natural
and Biological Control Agents
Fungi as Biological Control Agents of
Bemisia tabaci s.L.
Selection and Possible Genetic Manipulation
of Entomopathogenic Fungi for Biocontrol
Identification of Entomopathogenic Fungi
Attacking Bemisia tabaci in Israel
Effect of Accelerated Spore Germination
on Virulence of Paecilomyces fumosoroseus against the Whitefly,
Bemisia tabaci
Chemical Control of Bemisia tabaci
- Management and Application
A Simplified Feeding Bioassay System
for Adult Silverleaf Whitefly, Bemisia argentifolii
Role of Biorational Insecticides in the
Management of the Silverleaf Whitefly, Bemisia argentifolii
Sunday, 2 October evening: arrival and registration
Monday, 3 October: continue registration
Opening Session
Opening announcements D. Gerling
Welcome. Y. Vandia, Head, BARD
Poster session
Topic 1: Whitefly basic biology. Chairperson: D. Wool
T.M. Perring. Biological characteristics of B. tabaci and
closely related species
D.N. Byrne. Migration and dispersal by the sweetpotato whitefly
F.W. Tjallingii. Recording EPGs and honeydew excretion by the greenhouse
whitefly
P.G. Markham. Morphology of Bemisia populations
D.N. Byrne, A. Enkegaard. Discussion
Topic 2: Population dynamics. Chairperson: Y. Spenser
O.G. Riley. Population dynamics of Bemisia tabaci (and B.
argentifolii in agricultural systems
J.C. Allen. Spatio-Temporal modeling of silverleaf whitefly dynamics
in a regional cropping system using satellite data
Xu Rumei. Status of the occurrence and distribution of the sweetpotato whitefly (Bemisia tabaci in China.
T.J. Henneberry, G. Forer, S.E. Naranjo. Discussion
Tuesday. 4 October
Topic 3: Damage expressions of B. tabaci. Chairperson:
J. Coppedge
P.A. Stansly. Expression of plant damage by Bemisia
J.P. Shapiro. Insect-host plant interactions and expression of damage
D.L Hendrix. Bemisia honeydew
D.D. Oetting. Bemisia damage expression in commercial greenhouse
R. Yokomi, E. Kletter. Discussion
Topic 4: Viruses. Chairperson: J.E. Duffus
J.E. Duffus. Whitefly-borne viruses
M.K. Harris. A morphological study of Bemisia organ systems
of known importance in Homopteran virus transmission
B.W. Falk. Lettuce Infectious Yellows Virus: A bi-parasite Closterovirus
transmitted by Bemisia tabaci, and representative of a now
genus of plant viruses
E. Hiebert Whitefly-transmitted Geminiviruses
J.K. Brown, Y. Antignus. Discussion
Topic 5: Plant resistance. Chairperson: M. Pilowsky
S. Cohen. Plant resistance to Bemisia tabaci-borne viruses
J.W. Scott. lntrogression of resistance to whitefly-transmitted
Geminiviruses
C. Fauquet. Engineering plants for resistance to whitefly-borne
viruses
N. Kedar, J.W. Scott. Discussion
Y. Leshem Head, Israeli Society for nature Protection: Bird Migration
a lecture on nature, birds, airplanes and nature conservation
Wednesday. 5 October
Topic 6: International Cooperation in research and Control
Arrive at the Agricultural Research Organization, Bet-Dagan. Chairperson:
J.J. Mann
E. Sadan, Head ARO: Agricultural research in a rapidly changing
socio-economic environment
J.J. Menn The whitefly complex B. tabaci and B. argentifolii,
an international crop protection problem waiting to be solved
M. Kogan Area-,wide management of major pests vs. the agroecosystem
approach in IPM
N.C. Leppla Regulatory constraints to international cooperation
in controlling Bemisia tabaci and other pest outbreaks
B. Raccah The impact of international cooperation on the control
of whiteflies and aphids
J.C. Van Lenteren Scientific constraints to international cooperation
J.J. Menn, S. Elhanan, M. Kogan. Discussion
Thursday. 6 October
Topic 7: Biological control of Bemisia
Poster session. Chairperson: S. Steinberg
L.A. Lacey. Fungi as biocontrol agents for Bemisia
I. Barash. Selection and possible genetic manipulation of entomopathogenic
fungi for biocontrol of Bemisia K.M. Heinz. Predators and parasitoids as biological control
agents of Bemisia in greenhouses
K.H. Hoelmer. Parasitoids of whiteflies: Their potential as controlling
agents of outdoor population, of Bemisia spp.
M. Rose. Systematics of Eretmocerus (Hymenoptera. Aphelinidae),
an important parasite of Bemisia
D.A. Nordlund. Whitefly predators and their possible use in biological
control
D.A. Nordlund, R.A. Hall, 0. Minkenberg, D. Gerling Discussion:
"biological control possibilities"
Topic 8: Chemical and physical controls of Bemisia. Chairperson:
T.J. Henneberry
A.R. Horowitz. Chemical control of Bemisia tabaci, management
and application
D. Veierov Non-toxic formulations for the control of the sweetpotato
whitefly (Bemisia tabaci)
I. Denholm. Progress with documenting and combating insecticide
resistant
P.A. Stansly. Biorational pesticides
M.J. Berlinger. Physical means for the control of B. tabaci
T.J. Henneberry, 1. Ishaaya, Y. Dreishpoon. Discussion
Friday. 7 October
Topic 9: Integrated post management of Bemisia, an international
perspective. Chairperson: D.D. Kopp
O.D. Kopp. Introduction
G.W. Ferrentino. Integrated pest management of Bemisia@ in
ornamental gri
R. Ausher. Implementation of integrated pest management programs
in Israel
D. Gerling. Integrated pest management for the control of Bemisia
tabaci attacking field crops out-of-doors
P.C. Ellsworth Establishment of integrated pest management infrastructure
action program for sweetpotato whitefly management
Discussion - M. J. Berlinger
Prologue: Why is Bemisia still a pest
Presentation of different perspectives
E. Natwick - Growers, Y. Sachs - Plant protection, regulatory agencies,
W. Ravensberg - industry of beneficial organisms.
D.O. Kopp, Y. Sachs, E.T. Natwick W. Ravensberg, M.J. Berlinger.
Open discussion
R.T. Mayer Concluding remarks, resolution reading and closing
session
Optional trip to the Mormon University and Bethlehem.
An Assessment of the Biology and Management
Strategies of Bemisia spp. from an International Perspective TOPIC 1: BASIC BIOLOGY OF WHITEFLIES
Biological Characteristics of Bemisia tabaci and Closely Related Species
by Thomas M. Perring. Dept. of Entomology, University of California
Bemisia tabaci (Gennadius) has been among the most serious insect
pests facing world agriculture since its description over 100 years ago.
Recent evidence suggests that B. tabaci may be part of a species
complex. This group has evolved a number of characteristics that make
them well suited for rapidly exploiting a variety of habitats. In this
context, the biological attributes related to feeding, reproduction and
development of Bemisia whiteflies which contribute to their success,
and thus pest status, will be elucidated. While the biology related to
migration and dispersal is a crucial component, this topic is only mentioned
here (it will be covered in detail in the lecture by David Byrne at this
Workshop). As whiteflies complete migration to a new resource, they utilize
a variety of cues to select hosts. Once alighting takes place, predominantly
on lower leaf surfaces, whiteflies use mechanical and chemical receptors
to assess host quality initiating feeding biology. Receiving positive
feedback, intracellular probing initiates an intricate set of events which
ultimately result in stylet penetration of phloem tissue. This type of
feeding contributes to the success of Bemisia as a virus.
Validation, Refinement and Implementation of
Sampling Plans for Bemisia tabaci in Cotton
S.E. Naranjo, (Western Cotton Research Laboratory USDA-ARS, Phoenix, AZ),
P.C. Ellsworth, J. Diehl, T. Dennehy, ( Dept. of Entomology, University
of Arizona, Tucson, AZ) and H. Flint.
Reliable and cost-effective sampling methods are central to a study of
the biology and ecology of Bemisia tabaci and are a critical component
in the development of monitoring programs for pest management. We have
recently developed numerical and binomial sequential sampling plans for
immatures and adults. These plans enable the precise estimation of population
density and also allow us to classify populations for pest management
decision-making application. Validation and refinement are critical, but
often overlooked, phases in the development and implementation of robust
sampling plans. Our sampling protocols were implemented over a 60,000
ha cotton-growing area west of Phoenix, Arizona, in 1994. A large number
of fields (30-200) was intensively sampled on a weekly basis for irnmatures
and adults beginning in late May. This information was used to verify
and compare underlying spatial distributions with those specified in our
sampling models. A resampled algorithm was utilized on our field data
sets to test the overall performance of our sampling plans in terms of
achieving the desired sampling precision, and the accuracy with which
the correct decision was made regarding the need for pest control. We
further compared the accuracy and cost-effectiveness of using binomial
or numerical count data for decision-making. Results were used to refine
our sampling plans for future years. (P)
Spatial and Temporal Distribution of Fourth-Instar
Larvae of Trialeurodes vaporariorum and Bemisia tabaci in
Tomato Plants
A. Carnero, (Centro de Investigación y Tecnología Agrarias
- CITA, Tenerife, Canary Islands, Spain) and J.L. González-Andujar
(Instituto Nacional de Investigaciones Agrarias - INIA, Sección
Proceso de Datos, Area de Recursos Forestales, Madrid, Spain)
The interaction between the fourth-instar larvae of Trialeurodes vaporariorum
and Bemisia tabaci in tomato crops was studied. The larvae were
collected on different plants in Canary Islands greenhouses. The larvae
were counted weekly from all the leaves of the sampled plant.
Preliminary results showed that 85% of the total population of B. tabaci
and 84% of that of T. vaporariorum am distributed within the first
seven leaflets. Furthermore, the last three leaflets represent only 1.38%
of the total population of T. vaporariorum and 1.68% of the population
of B. tabaci, indicating that they are not representative of the
populations. We did not find a numerical relationship between the two
species. However, throughout the study period T. vaporariorum had
higher populations than B. tabaci and the greater population fluctuations.
Spatial and spatio-temporal distribution of
both species was similar within the leaflets. 'Mus, there was no niche
differentiation as a function of the spatial distribution of these specie.
(P)
TOPIC 3: DAMAGE EXPRESSION OF BEMISIA TABACI AND OTHER WHITEFLIES Bemisia Honeydew
Donald L. Hendrix and Terry Steele (USDA -ARS, Western Cotton Research
Laboratory, Phoenix, AZ)
Cotton fiber stickiness due to honeydew from insect infestations is a
severe problem cotton-producing countries. As much as 100 kg of honeydew
can be secreted on 1 ha of a infested crop. Since about 1987, cotton fiber
grown in the irrigated regions of the south U.S.A. has been particularly
susceptible to honeydew contamination from the silverleaf , Bemisia
argentifolii. Honeydew sugars on cotton fiber cause severe problems
in gins and textile mills, the fiber contamination leading to serious
cotton quality and marketability problems. Honeydews from Bemisia
and related homopteran insects have been chemically chard by gradient
anion HPLC (high performance liquid chromatography). Honeydews from insects
were found to contain distinctive sugar components. That from Bemisia
consists of 30 different sugars, some of which have quite unusual structures.
The major sugar comp (silverleaf whitefly honeydew is trehalulose [À-D-glc(I-1)-D-fru].
Besides trehalulose honeydew contains trehalose and several sugars which
contain the trehalose [-D-glc(l+--41)a-D-glc] in their structure. None
of these saccharine is found in the insect's of phloem sap which, in cotton,
contains only sucrose. Enzymes within the insect therefore convert dietary
sucrose to numerous oligosaccharides. From the chemical composition of
this sugar mixture, an enzyme preparation was de by a commercial firm.
which, when sprayed in an aqueous solution on honeydew-contaminated seed-cotton,
significantly reduces its stickiness as measured by either the minicard
or the detector test. (L)
A New Approach to Assessment of the Honeydew
Content of a Cotton Crop
H. Bar and A. Weinberg (Shenkar College of Textile Technology and Fashion,
Israel)
The damage inflicted by honeydew to the world's+ cotton crop amounts to
nearly 259, yield. Some of the honeydew-contaminated cotton is totally
unsuitable for processing in the industry and the rest loses some of its
value due to the stickiness of the cotton fibers. It is tt essential to
have a reliable method for assessing the degree of damage of cotton crops
by dew. The 'Shenkar Stickiness Tester - Model I' (SST-1) system was developed
for this f The SST-1 system can process samples of cotton, of approximately
80 g each, and render exact data of the honeydew they contain. The system
operates on the principle of opening the tested and of adhering all the
sticky points containing honeydew to a calender roll.
Introduction of an Exotic Whitefly (Bemisia)
Vector Facilitates Secondary Spread of Jatropha Mosaic Virus, a Geminivirus
Previously Vectored Exclusively by the Jatropha Biotype
J.K. Brown (Dept. of plant Sciences, University of Arizona, Tucson, AZ)
and J. Bird (College of agricultural Sciences, Mayaguez Campus, Experiment
Station, Rio Piedras, USA)
In 1992 whiteflies (Bemisia tabaci / argentifolii) colonized passion
fruit (Passiflora edulis) plantations, and virus-like symptoms
occurred on passionvine leaves in Puerto Rico for the first time. Disease
symptoms were reminiscent of those observed previously in the indigenous
weeds Jatropha gossypifolia and J. foetida infected by the
whitefly-transmitted Jatropha mosaic virus (JMV). JMV is known
to be transmitted exclusively by the nearly monophagous Jatropha
biotype of B. tabaci. Bean seedlings biolistically inoculated with
total nucleic acids purified either from passionvine plants infected with
the putative Passiflora Virus (PV). or from JMV-infected J.
gossypifolia, developed leaf curling symptoms, indicating the presence
of transmissible agents. In whitefly vector experiments, JMV was transmitted
from J. gossypifolia to P. edulis or to J. foetida
by the monophagous Jatropha biotype, but not by the B biotype.
However. transmission of JMV to passionvine occurred via the 'Jatropha
race' only when whiteflies were allowed to move freely between JMV source-plants
and P. edulis test-plants, but not when the vector WAS forced to
feed exclusively on non-Jatropha plants. In contrast, the B biotype
was capable of transmitting PV from P. edulis to P. edulis,
whereas the Jatropha biotype was not. 'These results suggest that
the Jatropha biotype may be responsible for the primary mobilization
of JMV from J. gossypifolia to P. edulis plantations, while
the B biotype is involved exclusively in secondary spread of inoculum
within the plantation. (P)
The Capsid Protein - A Determinant of Host Plant
Affiliations of Whitefly-Transmitted Geminiviruses?
J.K. Brown (Dept. of Plant Sciences, University of Arizona, Tucson, AZ,
USA), S.D. Wyatt (Dept. of Plant Pathology, Washington State University,
Pullman, WA, USA), and D.R. Frohlich (Dept. of Biology, University of
St. Thomas, Houston, TX, USA)
Seven contiguous, conserved motifs and the respective intervening, variable
regions of the coat protein of a library of whitefly-transmitted (WFT)
Geminivirus isolates were investigated at the nucleotide sequence level.
A region of approximately 550 bp of the coat protein gene was targeted.
Predacious Arthropods of Bemisia tabaci
on Tomatoes in Florida
D.E. Dean and D.J. Schuster (University of Florida, IFAS, Gulf Coast Research
& Education Center, Bradenton, FL, USA)
A survey of naturally occurring arthropods which attack Bemisia tabaci
(recently new species, Bemisia argentifolii) on tomatoes in southwest
Florida was conduct autumn of 1991 through the spring of 1993. A whole-plant
sampling method was u whiteflies and predators and leaf samples were used
for all mature stages of the many as 19 predacious arthropods were identified,
all of them generalist or facultative Other possible facultative predators
are pending confirmation or identification. The most abundant and consistently
encountered predators were an Anthocorid diosus, and a chrysopid,
Ceraeochrysa cubana. Although populations of 0. insidiosus,
Geocoris punctipus, Cardiasteihus assmilis and Chrysoperla
externa appeared to be high whitefly numbers, the characteristic delayed
response and lower reproductive these generalist predators prevented reduction
of the pest population prior to economic damage. The spider Theridula
opulenta was frequently found with numerous captured whitefly of the
remaining predators encountered appeared to be facultative feeders on
the whiter Further field assays will undoubtedly identify additional predator
species which a some stage of the whitefly. Methods of conservation and
augmentation may prove reducing whitefly populations, if predators can
be established earlier in the season. (P))
The Use of Macrolophus caliginosus as
a Whitefly Predator in Protected Crops
J. van Schelt (Berkel en Rodenrijs, The Netherlands)
The mirid bug Macrolophus caliginosus seems to Be a very promising
candidate fc of whiteflies. Although its developmental time is rather
long, this can be overcome b introductions in the crop. Preventive releases
are possible in tomato. M. caliginosus build up a population which will
affect the whitefly population. Combination with , enemies, for instance
Encarsia formosa, is necessary for an initial period of several Preventive
releases in other crops like cucumber and eggplant are less successful.
An source is needed for Macrolophus to develop well in these crops. M.
caliginosus will I Bemisia tabaci as well as on Trialeurodes vaporariorum,
both larval and pupal stages; who preference for one of them is still
under study. Mass production of M. caliginosus started in 1994 and the
first commercial app being conducted in tomatoes under glass and plastic
in Europe. Many aspects still ne, died, such as timing of the introduction,
numbers to be released, interval between releases; susceptibility to chemical
pesticides, phytotoxic effects because of its plant sucking habit, other
natural enemies, etc. The first results indicate that M. caliginosus is
achieving go the control of whitefly. Fine tuning IPM programs for each
crop still needs a lot Nevertheless, we think that M. caliginosus will
become part of biological control several crops.
The application of M. caliginosus is discussed
and results in tomato, eggplant, cucumber and gerbera are presented release
of Exotic Natural Enemies of Bemisia tabaci in the United States D.E. Meyerdirk (USDA, APHIS, PPQ, Hyattsville, MD, USA) R.D. Hennessey,
L. Wendel, J. Goolsby, M. Ciomperlik, and D. Vecek (USDA, APHIS, PPQ,
Mission Biological Control Laboratory, Mission, TX, USA)
Efforts to develop a biological control program against Bemisia
face continue in the United States. 'Me third year of a Five Year National
Research and Action Plan to Develop Methodology for Control and Management
of the Sweetpotato Whitefly is now in progress. The plan is a cooperative
effort with the following USDA services and establishments: Agricultural
Research Service (ARS); Cooperative State Research Service (CRSR) and
the State Agricultural Experiment Stations; Extension Service (ES) and
the Animal and Plant Health Inspection Service (APHIS). The APHIS Mission
Biological Control Laboratory (MBCL) in Texas serves as the key quarantine
facility for receiving most of the shipments of exotic natural enemies.
MBCL develops methods for recognizing morpotypes of genetic strains of
natural enemies including the use of genetic techniques (RAPD-PCR) to
distinguish species and strains. Foreign explorations for suitable biological
control agents have yielded 33 geographic strains or species of parasites
and predators which are presently being cultured at the APHIS National
Biological Control Laboratory in Mission, Texas. Countries searched by
ARS and Texas A&M University include Argentina, brazil Cyprus, Egypt,
Greece, India, Malaysia, Mexico, Nepal, Pakistan, Philippines, Spain,
Taiwan and Thailand. This resulted in 32 foreign shipments being received
into quarantine. Impact evaluation efforts are being conducted in the
Imperial Valley of Southern California, Rio Grande Valley of Texas, and
in Phoenix, Arizona. In California, three species or strains of Eretmocerus
from India (Padappai) and Texas, and one species of Encarsia from
the Nile Delta of Egypt are to be evaluated in 1994, while in Texas six
species or strains of Eretmocerus (Spain, Egypt, India and Texas)
and five species or strains of Encarsia (India, Egypt and Spain) will
be evaluated in the same year. In Arizona, two additional parasitoid species
will be evaluated. Studies also include inoculative releases of Eretmocerus
sp. in Arizona, California and Texas, and augmentative releases in spring
melons in California. Additional establishment evaluations are being conducted
in agricultural refuge crops and in urban hibiscus plantings in both California
and Texas. An Encarsia formosa from the Nile Delta of Egypt appears
to have promising regulatory qualities in the greenhouse. Mass production
of a coccinellid whitefly predator, Serangium parcesetosum, is
also being developed for augmentative studies. State cooperators are also
heavily involved in the evaluation of these exotic natural enemies in
greenhouse cropping systems. Local surveys of native natural enemies attacking
B. tabaci in the United States have recovered six Encarsia
spp., four Eretmocerus spp. and one Amitus species or strain.
Eight species of parasites have been collected in Texas, seven species
in Florida and five species in the desert southwest In general, in nurseries
and greenhouses, Eretmocerus spp. appear to be the most abundant
species. (P)
Foreign Exploration for Natural Enemies of Bemisia
tabaci s.L. A.A. Kirk and L.A. Lacey (European Biological Control Laboratory,
USDA -ARS, Montpellier, France)
Since 1991 foreign exploration for natural enemies of Bemisia tabaci
has been conducted by the USDA European Biological Control Laboratory
(EBCL). Parasitic Hymenoptera and fungal pathogens were collected in 12
countries (Austria, France. Spain, Greece, Cyprus. Egypt, India, Nepal,
Thailand, Malaysia and Brazil). Collections in spring of 1992 were planned
to coincide with overwintering and c populations of B. tabaci,
and its natural enemies in Spain, Greece, Egypt, Pakistan Nepal. A second
round of collections coincided with the end of the summer monsoon oi subcontinent
and the characteristic late summer buildup of Bemisia populations
in Spain in those areas were revisited in 1993. In March 1994 collections
were made in Thailand and Malaysia where conditions ranged from very hot
and dry to cool and humid. Seventy-four shipments of natural enemies were
made from the collecting area (ARS and APHIS) quarantine facilities in
the U.S.A. and our laboratory. Nineteen biotypes of Encarsia, Eretmocerus
mundus, other Eretmocerus and predator species, parcesetosum
(Coccinellidae), and Acletoxenus formosus (Drosophilidae), have been p
identified from the material collected. Several isolations of Paecilomyces
fumosoroseus and other, fungi were also collected. Parasitic Hymenoptera
collected by EBCL have been released in the US USDA/APHIS biocontrol Laboratory,
Mission. Texas, and their cooperators. These species of parasites, predators
and pathogens have been shipped from the U.S.A. quarantine facilities
to University and Government researchers for evaluation and biological
studies. Collections over a broad geographical range have provided information
on the distribution., the highly polyphagous 'B' biotype, also known as
Bemisia argentifolii; it has bee identified from Spain, Cyprus,
Egypt and Pakistan. (P)
Predators and Parasitoids as Biological Control
Agents of Bemisia in Greenhouses K.M. Heinz (Dept. of Entomology, Texas A&M University, College
Station, TX, USA)
Bemisia argentifolii (= the 'B' strain of B. tabaci) has displaced the
greenhouse Trialeurodes vaporariorum, as the most serious whitefly pest
problem of protected (greenhouse and glasshouse) crops worldwide. While
control of T. vaporariorum by the parasitoid I formosa may best illustrate
the successful use of augmentative biological control in Greenhouse crops,
biological control of B. argentifolii with releases of E. formosa has
yielded mixed results. Due to these inconsistent results, pre-introduction
evaluations of several other Bemisia nat were conducted to identify candidates
for use in inundative, inoculative or augmentative control programs for
greenhouse crops. Considering the results from these comparative evaluations,
it was hypothesized that the parasitoid Encarsia luteola and the predator
Delphastus pusillus, may be superior biological control agents relative
to E. formosa. Subsequent releases natural enemies into greenhouse-grown
poinsettia, infested with B. argentifolii, pro,comparable in quality and
price to a crop produced using a conventional insecticide-b control program.
One concern regarding multiple-species releases of natural enemies interspecific
interactions among biological control organisms may reduce their effective
the target species. This is a particularly important consideration when
control at required (as in the case of greenhouse ornamental crops grown
for their aesthetic natural enemies to compete for the same hosts. Laboratory
and greenhouse studies ha to quantify negative interspecific interactions
among three natural enemies, D. pusillus pergandiella and E. formosa.
However, population level studies indicate that the in interspecific interactions
is not strong enough to affect adversely the outcome of mt releases of
these natural enemies on biological control of B. argentifolii. (L)
Parasitoids of Bemisia tabaci in Cotton
in Santiago del Estero, Northwestern Argentina S. Helman (Zoología Agrícola, Universidad Nacional,
Santiago del Estero. Argentina), 0. Peterling (INTA Estación Experimental,
Santiago del Estero, Argentina) and M. Contreras (Zoología Agrícola,
Universidad Nacional, Santiago del Estero. Argentina).
Parasites of Bemisia tabaci were identified and the evolution of their
relative abundance in the cotton leaf samples in fields located in the
Santiago del Estero irrigation area (northwestern Argentina) was established.
The parasites were collected weekly during the cotton season from 1991
to 1994. The following parasites were found: Eretmocerus paulistus, Encarsia
porteri, Encarsia nigricephala and Signiphora sp. The most abundant species
was E. Paulistus&tus, followed by E. porteri. E. nigricephala and
Signiphora are not present in significant numbers, but an increase in
them was observed in the last part of the season. Among the species evaluated,
E. paulistus and E. porteri are those most deserving of future study.
(P)
Parasitoids of Whiteflies: Their Potential as
Controlling Agents of Outdoor Populations of Bemisia spp.
K.A. Hoelmer (USDA, APHIS, Methods Development, Brawley, CA, USA)
Parasitoids of many species are reported as attacking populations of Band
Malaysia worldwide, with varying degrees of effectiveness. However. Bemisia
continues to be a problem in many of these areas for various reasons,
including: (i) the taxonomic complexity of the Bemisia group impedes
identification of co-adapted parasitoids; (ii) the taxonomic complexity
of Eretmocerus and Encarsia, genera including most Bemisia
parasitoids, hinders proper identification of native and exotic species;
(iii) incomplete understanding of critical aspects of parasitoid biology
and behavior such as dispersal and host plant effects; (iv) the extensive
host range, complex host selection behavior, virus transmission and dispersal
behavior of Bemisia; and (v) the diversity of cropping patterns
of Bemisia hosts, all of which reasons contribute to the complexity
of effectively using parasitoids. Unlike whiteflies attacking perennial
crops, the temporal and spatial instability of annuals makes the task
of finding effective parasitoids of Bemisia particularly difficult
Short-duration crops grown in rapid succession favor the whitefly and
limit the buildup of parasitoids in each crop, unless extensive reservoirs
are present on native or weedy hosts. Crop phenology and diversity of
surrounding vegetation are therefore extremely important in the buildup
of whitefly and parasitoid populations. Seasonal augmentation or inoculation
may be helpful at critical times in agroecosystem without effective non-crop
refuges. For example, in the Southwestern deserts of the U.S.A., migration
helps the whitefly bridge gaps in desert agriculture where crops may be
widely separated by extensive desert and limited availability of host
plants. Non-crop reservoirs are limited largely to ornamentals in urban
areas. For parasitoids to be effective in desert crops they must be active
early in the season, when they are not naturally abundant.
Biological Control of Bemisia tabaci with Encarsia
formosa: A Realistic Option?
Joop C. van Lenteren, Klara Brasch and Heather Henter (Dept. of Entomology,
Agricultural University, Wageningen, The Netherlands)
Management problems associated with the recent introduction of the sweetpotato
(SWF), Band Malaysia tabaci, into West Europe initiated a search
for natural enemies to control greenhouse pest. We have examined the possibilities
of using the parasitoid Encarsia for control of Bemisia
in greenhouses. First, the host searching and acceptance behavior bionomics
of the commercially produced Dutch Encarsia strain were studied.
Ms parasitoid not perform very well on Bemisia. Next a strain of
E. formosa originating from Bemisia was evaluated. 'Mis paper reports
about the parasitization behavior of different E. formal on the
greenhouse whitefly, Trialeurodes vaporariorum, or on SWF larvae.
The strains or from either the greenhouse whitefly or the SWF show significant
differences in capability parasitizing the SWF. One of the strains seems
to be a promising candidate for control of B. tabaci and vaporariorum.
(P)
Development of Augmentative Biological Control
of Bemisia argentifolii on Field and Greenhouse Crops
Oscar Minkenberg, John Kaltenbach, Catie Leonard, Richard Malloy, Gregory
Simmons and Katie Ziegweid (Dept. of Entomology, University of Arizona,
Tucson, AZ, USA)
The imported whitefly Bemisia argentifolii has caused approximately
one billion damage to US agriculture since its first appearance in 1986
in Florida. The losses in 19 this whitefly are very likely to be similar
to previous years', indicating a need for further improvements in insect
pest management and substantial changes in agricultural practices. If
whit, pressure in an agricultural region can be maintained at a reasonable
level, biological control of augmentative releases of natural enemies
may be an option against whiteflies on field crops. or eliminating the
influx of adult whiteflies into a greenhouse crop is feasible and will
enhance the possibility for augmentative biological control in greenhouses.
We are examining augmentative biological control for four systems, viz.,
cotton, melons, greenhouse poinsettias greenhouse tomatoes. In addition,
we developed a mass-rearing of the native aphelinid w Eretmocerus
ex. Arizona in 1993. We are currently producing a few million wasps per
week fc evaluation research (the mass-rearing is sponsored in full by
CIBA Bunting Ltd., England).
Cotton: We have demonstrated that
B. argentifolii can be controlled by Eretmocerus, field
cages, and that a release rate of 4 to 32 Eretmocerus parasitoids
per plant is Releases of high numbers of parasitoids in field plots were
less successful; parasitism and whitefly densities in the release plots
were similar to those in the control plots (i.e., those with no parasitoids
released). A possible explanation is the immigration of high numbers of
adult whiteflies during June and July. A way to counteract the strong
increase in the adult whitefly population is to make use of the vertical
distribution of the various whitefly stages within the plant. The adult
whiteflies and eggs are on the top leaves, whereas the whitefly nymphs
and pupae, and it is hoped also the parasitoids, are located in the center
of the cotton plant An oil solution has a known deterrent effect on whitefly
oviposition and causes high mortality among young immature whiteflies.
This third season we arc, therefore, examining the possibility of combining
parasitoid releases and treatments of an oil solution on the top part
of the plant in a 28-ha trial in the Imperial Valley of California.
Melons: We have just started investigating
the impact of releases of the native Eretmocerus for whitefly control
and of Diglyphus wasps for leafminer control in a replicated field
cage experiment. The experiment will be conducted in three consecutive
crops and first results will be available at the end of this year.
Greenhouse Poinsettia: Evidence collected
by M. Hoddle, R. van Driesche (University of Massachusetts) and L. Sanderson
(Cornell University) from a trial in an experimental glasshouse, a replicated
cage study and a paired life-history study in the greenhouse indicates
that Eretmocerus is a biological control candidate against Bemisia
on poinsettia. This autumn we will conduct large-scale trials with Eretmocerus
on a Christmas crop in commercial settings in several states.
Greenhouse Tomatoes: Instead of a
trial-and-error approach to selecting an effective agent, we are comparing
several strains of Encarsia formosa. viz., ex. Egypt, ex. Beltsville
and a local one, for Bemisia control on tomatoes. We are screening
primers for RAPD-DNA technique to identify Encarsia wasps of various
strains; we are able to identify whitefly parasitoids at the species level.
Wasps of these three strains are being compared for their potential effectiveness
through behavioral and greenhouse assays. Trials in experimental greenhouses
showed almost 100% mortality in immature whiteflies after invasion by
E. formosa ex. Arizona. (P)
Systematics of Eretmocerus (Hymenoptera:
Aphelinidae), an Important Parasite of Bemisia
M. Rose, G. Zolnerowich and M.S. Hunter (Dept. of Entomology, Biological
Control Facility, Texas A &-M University, College Station, TX, USA)
Eretmocerus spp. are a significant component of the parasitic Hymenoptera
associated with Bemisia in the tabaci complex. To elucidate
differences that characterize species, nominal North American Eretmocerus
were redescribed from specimens. Foreign material has been acquired and
is being examined. Series of specimens reared from Bemisia in the
U.S.A. and abroad are being characterized, and crossing tests have been
initiated. Species of Eretmocerus and their characterization me
discussed. (L)
Host Killing and Time Allocation of the Parasitoid
Encarsia transvena
Noga Oster and Dan Gerling (Dept. Of Zoology, The George S. Wise Faculty
of life Sciences, Tel.-A viv University, Israel)
The parasitoid Encarsia transvena was introduced into Israel for the biological
contr Bemisia, and its biology and host associations are presently under
study. E. transvena i,-z nomous autoparasitoid that lays its female-producing
eggs in whitefly nymphs, where 'I! develop. Its male-producing eggs are
deposited in already parasitized hosts, and the male develop at the expense
of other whitefly parasitoids. Maximal oviposition takes place 3-5 following
the female's emergence. Preferred hosts for female production are t whitefly
nymphs and developmental duration is about 5-7 days to pupation and another
until adult emergence. Observations were conducted on 3-5-day-old females
that were allowed to walk or infested leaves. Each female was observed
continuously until she stopped showing interest whitefly patch and stood
still for at least 5 minutes. The activities registered during the o included:
standing stiff, preening, walking, handling, stinging and feeding. in
which ho was differentiated from honeydew feeding. Each incidence of presumed
oviposition was and the location of the whitefly nymph in question was
noted. At the end of each o period, the females were dissected and the
numbers of mature eggs that remained in u were counted. The number of
successful ovipositions was assessed by observing development in the whitefly
nymphs. Of the 15 females observed, 14 laid eggs; in 11, a significant
period of post-ovipositional stinging was observed, even after all or
nearly all of their eggs had been laid. Some of The ended in the host's
death. A comparison of time allocation during the ovipositional vs ovipositional
periods revealed no difference in host handling, but a longer time spent
and a shorter time spent in preening and standing still during the ovipositional,
as with the post-ovipositional period. This as yet unexplained behavior
of females that continue to sting, hosts despite their egg complement
having been depleted, contributes measurably to the of Bemisia tabaci.
(P)
Potential for Biological Control of Mixed Trialeurodes
vaporariorum and Bemisia tabaci Populations in Winter Tomato Crops Grown
in greenhouses
Judit Arno and Rosa Gabarra (Unidad d'Entomologia Aplicada, IRTA-Centre
de Cabrils. Barcelona, Spain)
Mixed populations of Trialeurodes vaporariorum and Bemisia tabaci
strain 'B' occur in winter greenhouse tomato crops grown along the Mediterranean
coast of Spain. Tomatoes are this region from September to April. In commercial
greenhouses weekly releases of Encarsia formosa were made from
mid September to the end of October using a release rate of two Lpupae
per plant. Leaflet samples were taken five times and brought back to the
laboratory parasitism levels and numbers of T. vaporariorum and
B. tabaci pupae were recorded separately density of whitefly pupae
in October ranged from 0.18 to 1.21 pupae per cm2. B. tabaci (main
species present at that time, and accounted for 72% of the pupae. In April,
T. vaporariorum, was the most abundant whitefly species and accounted
for 90% of the pupae. Although B. tabaci was the predominant whitefly
species in autumn, E. formosa was more often found parasitizing
T. vaporariorum. Maximum parasitism rates were found in November
for T. vaporariorum (36.8%) and in October for B. tabaci (5.3%).
In January, no E. formosa was found on B. tabaci, and parasitism
on T. vaporariorum never exceeded 7.6%. In our experiment E.
formosa was not able to control the whitefly within commercially acceptable
levels. Eretmocerus mundus, a native parasitoid, was recorded on
B. tabaci, but the parasitism rates never exceeded 2.9%. A mirid
bug, Cyrtopeltis tenuis, was found sporadically during the trial.
Other mirid bugs also known to be polyphagous predators were found in
the vegetation surrounding the greenhouses. Similar to E. formosa,
native parasitoids and predators were not abundant enough to keep whitefly
populations below damaging levels. (P)
Efficacy of the Fungus Aschersonia aleyrodis
and the Coccinellid Predator Delphastus pusillus, Used to Control
Bemisia tabaci in Greenhouse Cucumber
S. Steinberg and H. Prag (Biological Control Industries, Sede Eliyyahu.
Israel)
The capability of the entomopathogenic fungus Aschersonia aleyrodis
and the coccinellid predator Delphastus pusillus, alone and in
combination, to control the sweetpotato whitefly, Bemisia tabaci,
was tested in greenhouse cucumber. The study was carried out in four greenhouses
of 25 m2 area, each with 45 cucumber plants (cv. Turbo') evenly infested
with B. tabaci. Four treatments were conducted simultaneously,
each in a separate greenhouse: (i) control-no natural enemies applied;
(ii) A. aleyrodis - a single application of three consecutive sprays
at weekly intervals (commercial product obtained from Koppert Biosystems);
(iii) D. pusillus - a single application of three consecutive introductions
at weekly intervals, reaching an accumulative rate of three adult beetles
per m2 (commercial product manufactured by Biological Control Industries);
and (iv) both A. aleyrodis and D. pusillus with the introduction
schemes mentioned above. Both natural enemies, alone and in combination,
were able to suppress the whitefly population and delayed its increase
by about one month (= one generation time) compared with the control.
In that respect, no significant difference between the treatments of the
natural enemies was observed. maximum infection rate of A. aleyrodis
reached ca 60%. D. pusillus peaked at a level of ca 11 adult beetles
per m2 when applied singly, compared with ca six beetles per m2 when applied
together with A. aleyrodis. No negative interaction was found between
the two biocontrol agents in the laboratory tests. Suppression of the
whitefly population by both natural enemies was expressed in a significantly
higher yield in treatments relative to the control. The results indicate
that a single application of A. aleyrodis and D. pusillus
was effective for ca 2 months under the experimental conditions and that
a second application was needed to maintain continuous control of the
whitefly. Further experiments are currently being carried out in commercial
greenhouses of cucumber and melon. (P)
Global Distribution of Naturally Occurring Fungi
of Bemisia tabaci s.L. and Their Potential as Natural and Biological
Control Agents
L.A. Lacey (European Biological Control Laboratory, USDA-ARS. Montpellier,
France), R. Carruthers (Biological Pest Control Research, USDA-ARS, Weslaco,
TX, USA) and J. Fransen (Research Station for Floriculture, Aalsmeer,
the Netherlands)
Foreign exploration and intensified study of agroecosystems have revealed
a huge entomopathogenic fungi that attack Bemisia tabaci s.L in
nature and, under certain conditions epizootic that result in significant
control. The fungi that are most often reported as c naturally in B.
tabaci are the Hyphomycetes paecilomyces spp. and Verticillium
lecanii. Entomophthorales conidiobolus spp. and Zoophthora
radicans. Although considerable has been demonstrated for Aschersonia
aleyrodis as a pathogen of B. tabaci, it is not cc observed
infecting this whitefly under natural conditions. The fungus that is most
often causing epizootic in B. tabaci and the one with the greatest
geographic distribution is myces fumosoroseus. Epizootic have been reported
from subtropical areas of the USA, Mexico, Pakistan, India and Nepal.
The fungus is usually most prevalent in adult whiteflies, but high levels
of infection observed in nymphs. It is not known exactly where the sources
of primary inoculum are located and how epizootic are initiated. In the
cotton-growing areas of Pakistan, where hot dry are followed by monsoon
rains and spectacular epizootic in B. tabaci are caused by , soroseus,
initial inoculum might be located in the soil. In the lower Rio Grande
Valley c where some infected B. tabaci are found year round, the fungus
is probably transported fields by migrating adult whiteflies. Although
recent investigations revealed the possible fumosoroseus infections under
low relative humidity, high humidity are necessary for sp and continuation
of epizootic. The relation between climate, host plant, and the whitefly\
interaction is a complex one and needs further investigation. Natural
enemies of B. ta, other whiteflies may overlap in time and space with
fungal pathogens. The role inv natural enemies play in limiting or enhancing
the spread and prevalence of entomopathogenic,, in B. tabaci populations
also requires additional research. In studies involving Trialeurodes vaporariorum
it was found that the parasitoid Encarsia formosa and A. aleyrodis can
act i complementary manner and the wasp can even serve as a vector of
the fungus. (L)
Fungi as Biological Control Agents of Bemisia
tabaci s.L.
L.A. Lacey (European Biological Control Laboratory, USDA-ARS. Montpellier,
France) and JJ. Fransen (Research Station for Floriculture, Aalsmeer,
the Netherlands)
The epizootic potential of certain fungi in populations of Bemisia
tabaci s.L. w whiteflies has encouraged the commercial development
of entomopathogenic fungi as r control agents of whiteflies. This trend
has received additional impetus from the spread of the, highly polyphagous
silverleaf biotype. Four species of fungi: Aschersonia aleyrodis,
Verticillium lecanii, Paecilomyces fumosoroseus and Beauveria
bassiana, have beer currently being developed as microbial agents
against B. tabaci. Laboratory and greenhouse studies indicate good
potential of A. aleyrodis for microbial control of B. tabaci
and Trialeurodes vaporariorum, although the fungus is seldom reported
from B. tabaci in nature. A. aleyrodis performs particularly
well in greenhouses where high relative humidity and optimal temperatures
for fungal activity prevail. Recently, there has been commercial interest
in the development of A. aleyrodis in the Netherlands. Verticillium
lecanii has also demonstrated good biological control potential against
B. tabaci and other whiteflies, particularly T. vaporariorum.
It has been on the market as a microbial insecticide for the control of
aphids and greenhouse whiteflies for almost 15 years. Under greenhouse
conditions, good control has been observed with T. vaporariorum,
initial studies against B. tabaci have also revealed a good microbial
control potential. The requirement for high humidity limits its use to
those agricultural settings in which a relative humidity of >90% prevails
for at least part of the day. One of the species with exceptionally good
potential as both a natural and biological control agent of whiteflies,
including B. tabaci, is P. fumosoroseus. Under greenhouse
and field conditions, applications of P. fumosoroseus have resulted
in high levels of control of B. tabaci. Recent studies in the Rio
Grande Valley of Texas indicate the possibility for P. fumosoroseus
infections at relatively low humidity. Pending registration, the fungus
should soon be produced commercially in the U.S.A., Europe and Israel.
The development of fungi as microbial control agents of whiteflies is
still at a fairly early stage. Greater efficacy can be expected when the
full range of isolates has been evaluated and those best suited for producing
epizootic in a broader range of environmental conditions are selected.
Improvements in formulations, application methods and production efficiency
can be expected to increase insecticidal efficacy and the attractiveness
of these fungi for further commercial development. (L)
Selection and Possible Genetic Manipulation
of Entomopathogenic Fungi for Biocontrol I. Barash (Dept. of botany, Tel-Aviv University, Israel), H. Mor (Dept.
of botany, Tel-Aviv University), G. Gindin (Inst. of Plant Protection,
ARO, The Volcani Center, Bet Dagan, Israel), B. Raccah and Ben Ze'ev,
(Plant Protection and Inspection Services, Ministry of Agriculture, Bet
Dagan, Israel)
Selection of naturally occurring entomopathogenic fungi with high efficacy
against the target pest is currently the major method used for developing
mycoinsecticides. We have evaluated the intraspecific variability in pathogenicity
of Verticillium lecanii on Bemisia tabaci in relation to
genomic polymorphism as expressed by random amplified polymorphic DNA
(RAPD) and isozymes analysis. Thirty-six strains of V. lecanii
and other Verticillium spp. which were isolated from different
insect hosts and geographic locations were used for this study. Virulence
against larvae of B. tabaci within these strains ranged from 0
to 83%. RAPD analysis was performed on all strains using two different
arbitrary decamer primers and the calculated similarity coefficients were
subjected to cluster analysis using UPGMA. The dendrograins obtained from
the two primers were similar. 'Me amplification pattern by RAPD obtained
from the various isolates suggests that V. lecanii is a highly
diverse species. No correlation could be established between the RAPD
polymorphism and either pathogenicity or geographic location. Similar
results were obtained with isozyme analysis. Strains of V. lecanii
exhibiting the highest mortality in B. tabaci were isolated in
Israel from Myzus persicae and Acyrthosiphon pisum. However,
superior virulent strains of Verticillium sp., Beauveria bassiana
and Hirsutella sp., which also showed high tolerance to high temperature,
were isolated from B. tabaci in Israel. Selection of wild-type
isolates recovered from other insects or from widely different g geographic
areas vs selection of endemic isolates from the target host will be discussed,
as will t potential of genetic manipulation of entomopathogenic fungi
for biocontrol. (L)
Identification of Entomopathogenic Fungi Attacking
Bemisia tabaci in Israel
I.S. Ben-Ze'ev (Plant Protection and Inspection Services, Ministry of
agriculture, Bet Dagan), G. Gindin (Inst. of Plant Protection, ARO, The
Volcani Center Bet Dagan, Israel), I. Barash (Inst. of Plant Protection,
ARO, The Volcani Center, Bet Dagan and Dept. of Botany, Tel-Aviv University,
Ramat Aviv, Israel ) and B. Raccah (Inst. of Plant Protection, ARO, The
Volcani Center Bet Dagan, Israel)
The search for fungal pathogens of Bemisia tabaci in Israel is
relatively new. 'Me fungus, The first such fungus radicans (Zygomycotina:
Entomophthoraceae), was identified in July I unsprayed cotton field. During
1990-94 we isolated and identified six additional fungal p of B. tabaci.
Beauveria bassiana (Deuteromycotina: Moniliaceae) was isolated
in 1990, epizootic situation in a laboratory rearing (on cotton). Verticillium
lecanii (Deuteromycotina Moniliaceae) was isolated several times from
glasshouse populations of B. tabaci (larva, 1991-93. This fungus
was encountered in the months October-January, on ornamental p in glasshouse
populations reared on cotton. Conidiobolus coronatus and Conidiobolus
sp. (Zygomycotina: Ancylistaceae) (pending description as a new species)
were isolate, June-October in 1991-93, in a glasshouse rearing of B.
tabaci on cotton. The same gl population was found infected by an
apparently undescribed species of Verticillium. This in contrast
to the others mentioned above, attacks all stages of the host. Another,
yet uni Deuteromycete, possibly a Hirsutella sp. (Stilbaceae),
was isolated from two different, populations of B. tabaci in 1990
and 1991. (P)
Effect of Accelerated Spore Germination on Virulence
of Paecilomyces fumosoroseus against the Whitefly, Bemisia tabaci
Dorothy D. Peterkin and Richard A. Hall (National Institute for Higher
Education, Research, Science and Technology - NIIIERST, Port of Spain,
Trinidad, West Indies)
Bemisia tabaci is a major pest of vegetables in the Caribbean, causing
severe losses lion dollars (USA) in the Dominican Republic. Chemical control
is ineffective because of resistance. Pathogens are currently being investigated
as a possible component of a mull integrated pest management approach
to whitefly control. The fungus Paecilomyces fumosoroseuswas found to
be one of the most effective pathogens against whitefly under the condition
prevail in lowland tropical areas. Although it appears that a high humidity
microclimate may exist on certain parts of tl of some insects, thereby
permitting infection at low ambient humidities, infection will oc efficiently
during a'window'(usually at night) of high humidity. During the dry season
in and Tobago, this 'window' is rather short and so we have sought to
discover which factor influence the speed of conidial germination. The
nutrient medium on which the fungi cultured was found to be important.
When P. fumosoroseus was cultured on rice, the conidia produced gen-germinated
significantly faster than conidia harvested from comparable colonies cultured
on Sabouraud Dextrose Agar (SDA). Accelerated conidial germination was
directly =related into a faster infection rate and increased virulence.
In laboratory assays, third-instar whitefly nymphs were killed more rapidly
after inoculation with fully viable spores from a 14-day-old colony cultured
on rice than with similar spores produced on SDA. Spores from cultures
grown on rice, infected insects only 24 hours after being dipped in spore
suspensions (2.0 x 106 spores ml-'), half the infection time needed for
spores produced on SDA. LT50s and LC50s obtained for these faster germinating
spores were significantly lower than those for spores from SDA cultures.
Conidia of P. fumsoroseus produced on rice clearly germinate faster, infect
more rapidly and are more virulent than those produced on SDA. This method
of accelerating spore germination may be amenable to practical exploitation
by precise manipulation of the nutritional status of the culture medium.
(P)
Chemical Control of Bemisia tabaci - Management
and Application
TOPIC 8: Chemical and physical control of whiteflies and their resistance
to insecticides
A.R. Horowitz and 1. Ishaaya (Dept. of Entomology, ARO, The Volcani Center,
Bet Dagan, Israel)
In recent years the sweetpotato whitefly (SPW), Bemisia tabaci,
has become an increasingly serious pest of cotton, vegetables and ornamentals
throughout the world. Consequently, the immediate SPW management involved
chemical control, insecticide resistance management (IRM) programs and
improved application methods. In the last two decades, B. tabaci
control was based exclusively on conventional insecticides such as organophosphates
(OPs), carbamates and pyrethroids. However, in many cases sprays with
conventional insecticides did not achieve comprehensive control because
of the presence on the underside of the leaves of immature stages and
adults. In addition, the ability of SPW to develop rapid resistance to
most classes of existing insecticides exacerbated the situation. Continued
use of these compounds resulted in failure of whitefly control and a negative
impact on natural enemies and on the environment. At the beginning of
the 1990s, relatively selective insecticides with novel modes of action
and activities such as buprofezin, pyriproxyfen, diafenthiuron and imidacloprid
were found to be very effective for controlling developmental stages of
B. tabaci in cotton and other crops. The introduction of these
compounds into many countries, especially the U.S.A., has met with problems
in registration, resulting in continued use of conventional insecticides;
in many cases, combinations of compounds such as pyrethroids with OPs
or endosulfan are used to achieve reasonable control. In an effort to
control virus transmission by B. tabaci (especially the Tomato
yellow leaf curl virus), vegetable growers adopted a most deleterious
control practice: they repeatedly applied conventional insecticides (sometimes
daily), which resulted in rapid development of resistance and in control
failures. Hence, alternative methods of control are needed to suppress
the virus. In attempts to delay the onset of resistance in B. tabaci
to novel insecticides as well as to efficient conventional ones, an IPM-IRM
strategy was implemented in 1987 in cotton fields in Israel, accompanied
by an extensive resistance monitoring program. The main principles of
the strategy are: restricting the use of the insecticides to one pest-generation
period, alternating compounds with different modes of action (preferably
selective ones), and minimizing the number of treatments according to
a provisional action threshold (thus preserving natural enemies'
A Simplified Feeding Bioassay System for Adult
Silverleaf Whitefly, Bemisia argentifolii
Elizabeth W. Davidson and Rufino B.R. Patron (Dept. of zoology, Arizona
State University, Tempe, AZ, USA), Dusan Mitich and Donald L. Hendrix
(USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ, USA)
An assay system has been developed for the adult silverleaf whitefly,
Bemisia argentifolii feeding system accommodates the size and fragile
nature of the whitefly, allowing for the ingested agents against this
insect. This practical and cost-effective device is constructed from standard
disposable 1. materials. Whiteflies are harvested directly from the cotton
leaf and into a collection aspiration, minimizing physical trauma to the
insect. Insects feed through a nitrocellulose lose mixed ester membrane,
on a diet of 27% saccharose in an extract of zucchini. 'Me ir imidacloprid
was used to test the system. 'Mis system should allow for the testing
of ins, toxins, insect growth regulators, enzyme inhibitors and other
agents against the whitefly.
Role of Biorational Insecticides in the Management
of the Silverleaf Whitefly, Bemisia argentifolii
P.A. Stansly (University of Florida, Southwest Florida Research and Education
Center, Immokalee, FL, USA ), T.X. Liu and D.J. Schuster (University of
Florida, Gulf Coast Research and Education Center, Bradenton, FL, USA)
The term 'biorational' insecticide was coined but not defined in 1974
by Djerassi et al. 186:596). 'These authors characterized biorational
insecticides by their species-specificity ( city to non-target organisms)
in contrast to broad-spectrum chemical insecticides and ga, examples of
naturally derived and synthetic materials. We believe that the term biorational
I should be ' defined as natural or synthetic chemical agents which induce
mortality to specific targeted pest organisms, but are relatively inocuous
to non-target organisms, especially biological Control agents acting upon
the pest. Insecticides effective against the silverleaf whitefly argentifolii)
which might fit this definition include certain surfactants, oils, insect
growth regulator, and the systemic nitromethylene analogs (e.g. imidacloprid).
Detergents and oils have shown potential as suppressive agents for B.
argentifolii po on cotton and vegetable crops. Such materials have
low toxicity to many classes of organ possibility including parasitoids
and predators of whiteflies. We have been testing the insecticidal, repellent
properties of an insecticidal soap, a mineral oil, a surfactant-like extract
of Nicol, sei, and a pyrethoid (bifenthrin) against the silverleaf whitefly
and two of its natural enemies. All materials tested by leaf-dip bioassay
were highly toxic to young whitefly nymphs, but m and bifenthrin were
more toxic to all whitefly stages and more repellent to adults than the
dal soap or N. gossei extract. Residues of insecticidal soap and N. gossei
extract were toxic to adult whiteflies only when wet. The toxicity of
mineral oil and, to a lesser extent, insecticidal s greatly reduced when
applied with a Potter tower, whereas bifenthrin was equally toxic sprayed
or dipped. Thus, coverage was more critical to the functioning of oil
and soap depend on topical activity, than to bifenthrin - which has systemic
toxicity in the organism.
