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Project News 06.2004

A new whitefly species emerges as
a pest of cereals in Central America

All available newsletters > | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 |

  • Agenda
  • Abstracts
    • 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.

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