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Work Group on Bemisia tabaci
Newsletter No. 11. 1998

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Index >

• Status of Whitefly - Survey Results
• II International Workshop on Whiteflies and Germiniviruses in Puerto Rico
• The European Whitefly Studies Network
• Increasing infestation by Bemisia tabaci and spread of Red Cotton Disorder in West Africa
• Announcement
• Recent Publications
• Whitefly E-Mail Exchange Group

Status of Whitefly - Survey Results

During the second International Bemisia Workshop in Puerto Rico, we distributed a questionnaire among the participants in order to learn more about the present status of Bemisia in the world. We obtained responses from 10 countries. In addition, four more have later contributed information. We realize that this is a very scant sample of the status of a world-wide pest, but the results (Tables 1 & 2) are interesting and therefore merited presentation.

The questionnaire included information about the host plants, pest status, natural enemies, and control methods of Bemisia. The general method of control included insecticides, all of which were rather similar. It is noteworthy that several countries, including Australia, mention the severe problems of resistance. Thus indicating that the pest moves readily from locations in which it acquired resistance to insecticides to new areas. Likewise, most answers mentioned that the whiteflies move from one crop to the next. The most interesting results concerned host associations and natural enemies (Tables 1 & 2).

Table 1 indicates clearly that Bemisia is a pest of cotton wherever the latter occurs (except for Australia, where the present B strain of Bemisia has been recorded since 1993). It is also widespread as a pest of vegetables from the crucifereae, cucurbitaceae and solanaceae, and in some countries also of beans and of ornamentals, especially poinsettia. In some places, less usual crops are mentioned as hosts, such as tobacco, alfalfa, citrus and lettuce. Thus, although the sample is not large, the generalist nature of Bemisia and its capacity for increasing its range onto new crops is expressed.

Table 2 holds no surprises as to the occurrence of the two major parasitoid genera, Encarsia and Eretmocerus, that either occur naturally or have been introduced to combat Bemisia. The natural occurrence of Amitus is limited to the New World, and its occurrence in The Netherlands is due to its recent introduction. However, these may come from three different sources. Naturally occurring parasitoids of Bemisia, like Eretmocerus mundus and Encarsia lutea or transvena; introductions like Eretmocerus mundus in the US or Encarsia formosa in Europe; and the natural transfer of species from other, locally occurring whitefly species to the introduced Bemisia. The latter route became apparent again recently, when the newly occurring Bemisia populations in Australia, were found to be attacked by 5 new and 3 known Encarsia species and by three new species of Eretmocerus.

Although records of predators were presented, these often indicate how much more there is to learn about these important natural enemies. The only frequently recorded genera were Orius and Chrysoperla (or Chrysopa). Coccinellids of the genera Clytostethus, Delphastus, Nephaspis, Propylaea, Scymnus, and others, that are known as voracious predators of whitefly in the literature, were hardly mentioned, and additional heteropterous predators and mites were also reported only occasionally. This paucity of information, and the studies that should support it, is regrettable, especially in the light of recent results indicating the utility and the possibility for exploiting predators in whitefly management (e.g. Alomar, O., Goula, M., and Albajes, R. Mirid bugs for biological control: Identification, survey in non-cultivated winter plants, and colonization of tomato fields. IOBCWPRS Bulletin 17(5):217-223, 1994).

II International Workshop on Whiteflies and Germiniviruses in Puerto Rico

Submitted by: R.T. Mayer

The 2nd International Workshop on Whiteflies and Germiniviruses was held in Puerto Rico from 7-12 June 1998. As the name implies, we have joined forces this time and tried to bring together the workers on the two aspects of Bemisia-mediated damage: those attributed to the insect and those to viruses. This was a change from the 1st International Workshop (Shoresh, Israel, 1994) in which virus-related problems were dealt with in the general framework of the meetings. It reflected the growing prominence of Bemisia-transmitted viral plant diseases in the plant protection scene and the needs and desires of both virologists and entomologists to have information and exchange ideas. This workshop was a joint venture between the 2nd International Symposium on Geminiviruses and Their Vectors (chaired by Dr. Doug Maxwell, Department of Plant Pathology, University of Wisconsin, Madison, WI) and the International Bemisia Working Group (chaired by Dick Mayer, USDA, ARS, U. S. Horticultural Research Laboratory, Orlando, FL). About 300 people were in attendance at the workshop from 27 countries. Workshop sessions of common interest were held in the morning sessions and topics more narrowly related to entomology or virology were held in the afternoons and evenings. This gave participants an opportunity to attend more diverse presentations than would be possible at individual meetings of the two groups. Sessions were arranged with a slate of invited speakers followed by discussion, comments, and questions. There were 107 formal lectures and 71 posters presented at the meeting, covering topics from production of plants resistant to geminivirus and whiteflies, to cultural practices to limit the incidence and severity of viruses and whiteflies. In addition to the formal program, there was a practical workshop by M. Nakhla, P. Ramírez and D. Maxwell on the use of PCR and DNA hybridization for identification of geminiviruses. Professional credits for workshop attendance were given. A bus tour to a tropical fruit farm and a social event sponsored by the Puerto Rican Department of Agriculture provided ample time for scientists to meet and interact while enjoying the local hospitality and scenery.

Since most participants of the workshop found it interesting and useful, discussions were held as to the venue and date of the 3rd proposed workshop. It was decided that the interaction with the gemini-virologists was beneficial, and since they have decided to conduct their next meetings at the John Innes Institute in Norwich, U.K., and since that locale has extended its invitation to our group, we shall join them for the 3rd Workshop. Thus, the tentative venue and dates of this Workshop are:
The John Innes Institute, Nowitch, UK, summer of 2001.

As the workshop will only take place in three years, it is a good time to plan ahead and make sure that we get the best possible benefits from our efforts. The following members of the international research community have volunteered to help in the organization of the workshop. However, we need and would welcome additional help, and call upon anyone willing to participate in the organization of the workshop to contact Dan Gerling. The interim list of members of the organizing committee for the third Bemisia workshop are:

It is also useful to raise ideas and concerns that may help in improving the program of the 3rd Workshop, while the results and conclusions of the previous meetings are still fresh. Some ideas are presented below and any comments and/or lists are very welcome.

1. The information passed to the audience in a workshop is intended to be the basis for the generation of ideas, rather than the conveyance of facts. Therefore, it is necessary to combine transfer of information with exchange of ideas. However, time is limited and information transfer is essential in order to generate intelligent discussions. Therefore, it is beneficial to limit the lectured information transfer to the minimum. This can be achieved by circulating the abstracts and/or the full presentation manuscripts at least one month prior to the meetings, or by limiting presented papers to an absolute minimum - enabling extra time for discussion.
   
   
2. Fruitful discussions require guidance; panels who are familiar with the material and who can raise the most pertinent issues should therefore, chair discussion periods.
   
   
3. As germiniviruses are not the only viruses transmitted by Bemisia (and the numbers of the latter are growing), it will be necessary to think about an appropriate system of incorporating additional virological aspects into the program.
   
   
4. The importance of basic studies in physiology, biochemistry and molecular biology, for understanding Bemisia is on the rise. A way must be found to represent this aspect and to convey it forcefully and effectively without becoming too technical for the diverse scientists.

The European Whitefly Studies Network - EWSN

Submitted by: Dr. Ian Bedford

Coordinated by:-
Dr. Ian D. Bedford, John Innes Centre, Norwich, UK
Dr. Michael de Courcy Williams, Horticulture Research International, Wellesbourne, UK

Under the European Union Framework IV programme, a Concerted Action proposal has recently been approved for us to establish a network of European scientists and industrialists involved in the study and control of whiteflies and their associated problems within European agriculture. Twenty seven participants from fifteen different countries will be funded by the programme to attend workshops and meetings, along with an additional twenty three members supported by Novartis and Koppert.

The network has been entitled, the European Whitefly Studies Network (EWSN), and has the following three main objectives:

1. To establish and formalise links between whitefly researchers within Europe.
2. To collate information on European whitefly related problems and current research.
3. To improve exchange of information between researchers.

These objectives should lead to a better understanding of the current whitefly-related problems within Europe, allow evaluation of the research priorities and hopefully prevent duplication of studies in different laboratories. The aim is, therefore, to create an interactive network which will strengthen each research programme, stimulate new areas of collaborative research, and augment the availability of research results to plant health organisations, related industries and growers. The network encompasses five main areas of whitefly research, Virology, Epidemiology, Natural Enemies, Faunistics, and Plant Protection. Our first workshop, to be held at the John Innes Centre, Norwich, Norfolk, UK in May 1999, will enable us to establish the present levels of research within these five disciplines and identify cross-discipline links that may benefit studies. Three working group meetings are then planned over the following year to develop reliable and acceptable protocols between participants who are involved in similar studies.

By establishing this interactive network, we can collate data on many aspects of European whiteflies and the associated problems that contribute to their high pest status. 'EWSN' involves participants from Europe with a wide range of skills and experience whose interaction will improve the transfer of technology across Europe. Information gained from this network will assist the development of whitefly control methods that, in turn will help increase crop yields and reduce insecticide inputs. 'EWSN' will also help to assess both the possibilities and consequences of whitefly and whitefly-transmitted plant viruses that are already within southern Europe, spreading into northern Europe and into countries that are presently whitefly exclusion zones. By producing a comprehensive web site, we will be able to make this data available to all interested parties, provide all the participating research centres with a modern forum for presenting research results, and promote the output of this work programme that this Concerted Action aims to instigate within Europe.

Our second workshop will be hosted by Professor Carmelo Rapisarda at the Institute of Agricultural Entomology in Catania, Sicily in 2000. We plan that an open meeting will be held on the final day of this workshop, to which all interested parties can attend.

Increasing infestation by Bemisia tabaci and spread of Red Cotton Disorder in West Africa

Submitted by: S. Nibouche and M. Vaissayre, Entomologists of the Cirad-CA, Cotton Program. France

Until the 1980s, the presence of Bemisia tabaci in cotton crops in sub-Saharan Africa was associated with problems of sticky cotton and the spread of viruses. However, a new cotton disorder linked with B. tabaci infestations appeared in northern Cameroon at the beginning of the 90s. From 1991 onwards, the phenomenon, known in French as "maladie des cotonniers rouges" or MCR, spread to 30,000 ha and caused serious damage. The disorder has remained limited to the same region for eight years, with a few occasional cases in the rest of the northern Cameroon cotton belt. The symptoms of MCR are a wine-red coloring of the foliage followed by very rapid wilting of the plant. The color appears simultaneously in all the cotton plants in a field, and does not occur until the first bolls start to open. Little is known of the etiology of MCR. There are certain similarities with that of physiological disorders such as squash silvering and irregular ripening of tomato insofar as no pathogen has been found. First studies comparing Cameroon B. tabaci populations with B biotype through RAPD-PCR did not give conclusive results. These studies are continuing. Very strong outbreaks of B. tabaci were recorded in Burkina Faso and Mali in 1998. Linked with these, the red cotton disorder appeared in bothcountries, affecting almost the whole cotton area in one of them (representing about 250,000 ha of cotton). Senegal has been affected by very strong B. tabaci outbreaks since 1997 but the red cotton phenomenonhas not been observed. It would thus seem that after being a minoroccurence, red cotton disorder is becoming a serious threat to cotton growing in West Africa.

Announcement

The 1999 edition of "Bibliography of Bemisia tabaci (Gennadius) and Bemisia argentifolii Bellows & Perring" will be available for downloading on the USDA-ARS, Western Cotton Research Lab homepage in early February 1999. The 1999 edition includes the entire database (current through the end of 1998) and the 1998 addendum which includes citations cataloged during 1998. The databases can be downloaded in ProCite (2.11 for DOS and 4.03 for Windows 95), Word 7.0, or ASCII text format. The databases are also available on diskette upon request from S. Naranjo.

Recent Publications

• J. Huang and A. Polaszek. 1998. A revision of Chinese Encarsia. Journal of Natural History 32(12) 1825-1975.
  
  
• Naranjo, S. E. & J. R. Hagler. 1998. Characterizing and estimating the impact of heteropteran predation. Pp. 170-197. In: M. Coll & J. Ruberson (eds.), Predatory Heteroptera: Their ecology and use in biological control. Thomas Say Symposium Proceedings, Entomological Society of America.
  
  
• Naranjo, S. E., P. C. Ellsworth, C. C. Chu, T. J. Henneberry, D. G. Riley, T. F. Watson, and R. L. Nichols. 1998. Action thresholds for the management of Bemisia tabaci (Homoptera: Aleyrodidae) in cotton. Journal of Econonic Entomology 91: 1415-1426.
  
  
• Gerling, D., & S. E. Naranjo. 1998. The effect of insecticide treatments in cotton fields on the levels of parasitism of Bemisia tabaci. Biological Control 12: 33-41.
  

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