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Bemisia Newsletter >

Project News 06.2004

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

Work Group on Bemisia tabaci
Newsletter No. 13. Summer 2000

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

Index >

Introduction

by D. Gerling (Tel Aviv University, Israel)

The idea of establishing a newsletter to serve those interested in Bemisia research took shape during the 1984 symposium on Bemisia at the International Congress of Entomology in Hamburg, Germany. At that time, the pest was spreading and all agreed on the dearth of knowledge regarding the people working in the field, the limited availability of relevant literature as well as the extent to which the pest was causing damage. The appearance of the first newsletter shortly thereafter contributed to forming a loosely knit workgroup of those who were interested in various aspects of the topic.

Since then, our knowledge of the Bemisia complex and its agricultural, physiological and evolutionary ramifications has increased greatly [from fewer than 800 publications produced between 1889 and 1986 (when Bemisia tabaci was described by Gennadius) to ca. 3500 produced since]. Bemisia has spread to most of the known tropical, subtropical and temperate agricultural regions, becoming a pest of both greenhouse and outdoor crops. New virulent types of species and strains have been discovered, and it is currently the focus of worldwide, state-of-the-art activity concerning the determination of its taxonomic status.

The means of disseminating knowledge have also changed, and information is available on numerous topics through e-mail and Internet connections. Thus the functions a newsletter such as ours have also changed and we believe its main present importance lies in attempting to provide those interested in Bemisia with clear and concise summaries of what is known and what is being done in Bemisia research.

In the present issue, we decided to concentrate upon the taxonomic status of Bemisia, its potential as a viral vector and the state of knowledge regarding some of its natural enemies. We believe that clear and concise information on these topics, which stand at the forefront of Bemisia research, need to be shared by all those in the field, who will then be able to utilize this information in their own work.

Bemisia tabaci - How Many Biotypes Are There?

by G.K. Banks (School of Biological Science, University of Wales) and P.G. Markham (Department of Virus Research, John Innes Centre, UK)

Since the mid-1980's when B. tabaci emerged as a major pest in the USA, causing agricultural losses of millions of dollars (Perring et al., 1993), there has been an urgent need to resolve the taxonomy and to understand more about the biology of B. tabaci worldwide. Biological differences amongst B. tabaci populations were already described based on virus transmission, host plant preference and fecundity (Costa and Brown 1991; Brown and Bird 1992; Bedford et al., 1992; 1994). One of the initial biochemical studies on samples of B. tabaci representing a worldwide geographic range involved isoenzyme analysis, and 12 distinct non-specific esterase profiles were obtained (Brown et al., 1995). Currently there are twenty distinct esterase patterns published for different populations of B. tabaci over the world (Brown et al., 1995; Rosell et al., 1997 and Banks et al., 1999).

Until recently the naming of biotypes has been based on these esterase profiles, and their unique patterns have been the main criteria for the differentiation of and reference to populations of B. tabaci. However, molecular analyses have now provided data that allow the genetic relationships among biotypes to be studied and compared. Dendrograms produced from genetic similarities based on randomly amplified polymorphic DNA (RAPD)-PCR and amplified fragment length polymorphism (AFLP) analyses (Guirao et al., 1997; Cervera et al. in preparation) along with molecular phylogenies, constructed from sequences of mitochondrial and nuclear genes (Frohlich et al.,1995; 1999; De Barro et al., 2000; Banks et al., in preparation) all show remarkable similarity in their delineation of relatedness of different populations. These studies, however, group together some populations that have unique esterase patterns and this raises the question of what constitutes a biotype for nomenclature and diagnostic purposes and what really defines a biotype in genetic and biological terms. If identification is required for quarantine purposes then this information can be best obtained by methods such as esterase analysis or RAPD PCR, although these techniques are not foolproof, especially in highly polymorphic populations, e.g. within populations associated with cassava in Africa (Legg et al., 1994). Phylogenetic studies have shown that there are there are distinct groups of related whiteflies that can be separated using molecular markers and that there are genetically similar populations present over a wide geographic range. The number of clades varies according to the size, composition, and geographic origin of the data set; therefore, there cannot be a fixed number of groups using this method. The most comprehensive studies to date show that there may be as few as a five to seven clades worldwide. Molecular phylogenetics supports the evidence that a population of silverleafing whitefly, formerly called the B biotype, has been transported round the world. It also shows that there is genetic diversity within a B biotype clade in contrast to what was first assumed (De Barro et al., 2000; Banks et al., in preparation).

The classification of B. tabaci is still unresolved and a subject of scientific debate, and the naming of the B biotype or silverleafing whitefly as a new species, B. argentifolii is still contentious. The combined evidence from detailed morphological studies (Rosell et al., 1997), molecular phylogenies (Frohlich et al., 1995; 1999; De Barro et al., 2000; Banks et al., in preparation) and interbreeding experiments (Rondo et al., 1999 in preparation) strongly tends to support a species complex theory and not the present systematics of B. argentifolii as a discrete species from other populations of B. tabaci. No doubt the debate will continue until enough data is collated to maintain or reverse the present classification.

Bemisia tabaci - What’s in a Name?

by P. De Barro, P.J. Driver, F. Schmidt, S. Naumann, I. McKenzie, J. Curran (Whitefly Research, CSIRO Entomology, AU)

The question over the nomenclature of Bemisia tabaci came to the fore with the renaming of the B biotype to Bemisia argentifolii. There is no doubt that B. tabaci is a highly variable species. There are numerous papers that describe differences across a wide range of biological and genetic parameters. Together these differences have been used to characterise numerous biotypes and were the basis for the renaming of the B biotype. However, many of the differences, especially the morphological and biological ones, exhibit remarkable plasticity.

One of the key supports for the argument was the sexually incompatible between the A and B biotypes. Unfortunately, this alone though is not enough. Sexual incompatibility can be due to factors such as cytoplasmic incompatibility and behavioural isolation, and while they may be driving forces that lead to speciation they are not in themselves proof of species differences. Further, sexual incompatibility is not unique to the B/A interaction, as it is known to occur between several other biotypes.

Two recent papers, Frohlich et al. (1999) and De Barro et al. (2000) shed further light on the problem. By comparing a number of nuclear and mitochondrial gene regions from individuals taken from a large number of geographic areas the authors have been able to examine the phylogenetic structure of the B. tabaci complex. The results show that there is a strong geographic structure to phylogenetic trees generated. This structure raises the following issue. The sister clade to the B biotype are the non-silverleafing populations from Egypt, Spain, Sudan and Nigeria. The next closest relative is the cluster of populations from the Americas which includes the A biotype. If the A biotype is B. tabaci and the B biotype a different species then we have to rename the Egypt, Spain, Sudan and Nigeria population. This then raises the issue of the correct taxonomic designations for the remaining four clades from Asia, Australia and West Africa. Taken to its logical conclusion, the monophyly of B. tabaci becomes open to serious doubt..

Perhaps the best way to view B. tabaci is as a complex belonging to the one species with distinct geographically based populations that exhibit variation across a number of traits. There is certainly insufficient data to support the raising of any biotype to new species status and therefore the use of B. argentifolii should be discontinued.

An Overview of the European Whitefly-Transmitted Virus Problems

by I. Bedford (John Innes Centre, UK)

Presently, over a thousand different whitefly species have been identified. Most of these exist in the tropical and subtropical regions of the world, although some are common throughout the more temperate regions and can survive the cold winters of northern Europe.

Over the recent years a few whitefly species have however, become serious pests of certain crops within important agricultural regions and many of these pest species are now present within the European boundaries. Aleurothrixus floccossus, the citrus whitefly, for example is currently a great problem to citrus growers in southern Europe where large infestations distort leaves, soil fruits and reduce yields, and spiralling whiteflies, such as Aleurodicus dispersus and Lecanoideus floccissimus are now causing phenomenal damage to tropical fruit and ornamentals in the Canary Islands, where crops such as banana are having their leaves sucked dry by massive infestations of these pests.

Despite the severe damage these whiteflies are inflicting, by direct feeding, they do not compare with the problems caused by the few whitefly species that can also acquire and transmit plant viruses. At present, only three whitefly species are known to vector plant viruses. One of these, the banded whitefly, Trialeurodes abutilonea, is only found in North America, yet the other two, the glasshouse whitefly, T. vaporariorum and the tobacco whitefly, Bemisia tabaci are currently found on every continent and are both well established within mainland Europe.

As vectors of plant viruses, the Trialeurodes species only appear capable of transmitting a few viruses within the closterovirus group, whereas B. tabaci can acquire and transmit over 60 different viruses, which include Clostero-, Luteo-, Poty-, Carla- and Nepoviruses along with a large number of geminiviruses. The vast majority of these viruses are found within the warmer regions of the world, particularly Asia, Africa and South America, and are often associated with indigenous weed species. A long- established co-existence between the virus and the host plant has usually resulted in dramatic symptoms, often a vivid yellow-veining which appears to have little effect on plant development, enabling them to grow, flower and set seed. However, as agriculture has spread into new areas, some of these viruses have also infected important crop plants, such as tomato and cucurbits, often with decimating effects.

The potential for these viruses and vectors to spread into new locations and infecting new hosts, has also become greater as temperate regions of the world become hotter and the worldwide trade in ornamental plants and exotic produce continues to expand. In fact, the past decade has already seen an alarming increase in whitefly-transmitted virus problems within Europe.

Initially, a closterovirus similar to beet pseudo yellows (BPYV), and transmitted only by T. vaporariorum to cucurbit crops, was the only whitefly virus problem within areas of southern Europe but, in the mid 1980's. However, as B. tabaci became more of an agricultural pest, a geminivirus it acquired and transmitted, began infecting tomato crops in Italy and Sicily. This was named Tomato yellow leaf curl virus - 'Sardinian isolate' (TYLCV-Sar), and identified by a distinctive inter-veinal yellowing and often a severe leaf curling. It also caused stunting of infected plants and a dramatic loss in yield.

During the early 1990's, TYLCV-Sar spread into most of the major field and protected tomato crops along the south and south eastern regions of Spain including the intensive horticultural region around Almeria. The scale of the resulting epidemic and associated yield losses generated considerable concern for the future of an industry that supplies over 750,000 tonnes of tomatoes to northern Europe each year; It also triggered many related research projects.

Concern that this virus could ultimately spread into the glasshouse tomato crops of northern Europe and even threaten the UK’s tomato industry, led to the establishment of quarantine legislation, plant health passports and a notifiable pest status for B. tabaci. There is also legislation to prevent non-European B. tabaci from entering Europe, which is aimed at reducing the risk of introducing new viruses to the continent.

The original source of TYLCV-Sar has never been established, but it does appear to be unique to the Mediterranean basin. However, UK and Spanish whitefly scientists, who formed a small collaborative network in 1996, undertook a number of epidemiological studies on this virus. One of the studies identified the very common European weed, black nightshade, Solanum nigrum, as an excellent reservoir for both the virus and the whitefly vector. It is possible that TYLCV-Sar first spread from this weed into tomato for the first time in the 1980's, but it almost certainly now plays an important role in the continuation and spread of the virus, particularly where it grows within field crops.

As B. tabaci - related problems have continued, growers have understandably increased the use of insecticides. This has not always solved the problems, and many have dramatically escalated, particularly where viruses are concerned. However, Trialeurodes problems appear to have lessened, where B. tabaci have increased probably due to their inability to compete, particularly in the hotter months of the year. This has had a dramatic effect on the Trialeurodes-transmitted cucurbit virus, which seems to have been totally displaced by a similar closterovirus that is transmitted by B. tabaci. - Cucurbit yellow stunting disorder virus (CYSDV). This new virus presently infects almost every plant within every cucurbit crop within the Iberian peninsula, producing symptoms that begin as a leaf mosaic then develop into a full yellowing as the leaf matures.

In 1995, TYLCV appeared for the first time in Portugal, on tomato plants within the Algarve. The outbreak was very severe and had affected very young tomato plants. Since the symptoms of whitefly-transmitted viruses appear about two weeks after inoculation, it seemed probable that the Portuguese tomatoes were first infected soon after germination and maybe within a nursery. Molecular studies using DNA probes subsequently found this virus to be different to the one that was already in Spain, although it was identical to a tomato virus that had been endemic in the Middle East since the 1960's. This had been named TYLCV - Is (the Israeli strain).

Although TYLCV-Is is transmitted by B. tabaci and produces similar symptoms to those of TYLCV-Sar, it has a different alternative host range. TYLCV-Is does not infect S. nigrum, yet readily infects other common weeds such as, Datura stramonium, and various Nicotiana species. It has also been found to infect an exported ornamental plant, Lisianthus, offering a possible explanation for the source of the first outbreak, probably within a nursery where infected ornamental plants and tomato seedlings were being grown in close proximity.

Whatever the cause, this new virus, spread through tomato crops in the Algarve very rapidly, and by 1997, had reached the tomato crops within southern Spain, co-infecting plants with the Sardinian strain. Due to the severity of symptoms, many tomato growers have been forced to replant greenhouse crops up to 3 times during the summer months and, around the Malaga region, growers have recently had to abandon the growing of outdoor tomato crops.

On top of these increased problems to the tomato industry, the appearance of the Israeli virus has brought additional fears to growers within southern Spain as this TYLCV severely infects green beans (Phaseolus vulgaris) and more recently sweet pepper plants.

The speed at which this new and decimating virus has become established within southern Europe, where its insect vector and susceptible hosts are present, has strongly underlined the importance of monitoring plant movements and checking for pests and diseases on all imported plant material in the future. It has also emphasized the necessity to uncover and risk assess any other whitefly-transmitted viruses that may already exist in Europe, as demonstrated by the recent discovery of a geminivirus infecting Ipomea Indica near Malaga. However, laboratory experiments have subsequently found that it could not be transmitted to other plant or crop species.

As a direct result of the UK-Spanish collaborative successes and the urgent need to address the continued escalation and spread of whitefly problems in southern Europe, the European Whitefly Studies Network (EWSN), was established. Funded by the EC under the FAIR 6 programme (CT98 4303) this Concerted Action initially involved 27 scientists within 13 different European countries. However, with the support of Novartis AG and Koppert Biological Systems (who are both actively involved in EWSN), a further 18 European scientists are able to participate in the network.

EWSN began with the following three objectives:

  • To establish and formalise links between whitefly researchers in Europe.
  • To collate information on European whitefly related problems and current research.
  • To improve the exchange of information between researcher

An initial workshop was held at the John Innes Centre, Norwich, UK (May 3rd - 7th 1999), that enabled delegates to present and discuss all current whitefly research topics within Europe as well as review the present agricultural problems. Five separate discipline groups were also established, covering virology, epidemiology, systematics, natural enemies and plant protection.

Three specialised working groups were then planned for 2000, to enable participants within any of the discipline groups to review and standardise associated methodologies and techniques.

The first of these working group meetings was held at Stuttgart University, Germany, in March 2000 which has enabled 14 molecular virologists within EWSN to standardise reliable and reproducible protocols for identifying and characterising whitefly-transmitted viruses in Europe.

The second meeting is being held at the John Innes Centre, from 17th - 20th May 2000, where delegates are going to review and determine the most effective methods, for identifying and characterising whitefly species, biotypes and natural enemies. This will cover taxonomic, biochemical and molecular techniques.

During December 7th - 9th 2000, the third working group meeting will be held in Spain at the new Koppert facility in Aguilas. This meeting will enable EWSN members involved in whitefly pest management and IPM, the opportunity to examine and compare successes and failures of chemical, biological and physical control systems throughout Europe. It is hoped that this meeting will also involve representatives from countries outside of Europe that have been managing whitefly problems successfully for many years.

At the end of February 2001, the EC funding for EWSN finishes, and the project will conclude with a workshop to review the achievements that have been made over the previous two years. This will then be followed by an international whitefly symposium that is being organised by EWSN at Ragusa, Sicily within the University’s, faculty of Agriculture.

EWSN has, during its first year grown from strength to strength and demonstrated beyond doubt its important role within European crop protection. It is hoped that after the EC funding finishes, EWSN will continue to operate for as long as possible, although this will obviously depend on securing the necessary financial support which will be sought over the next few months.

EWSN presently has over 60 members, creating an infrastructure that links research laboratories with related industry, field support services and ultimately the growers that are affected by whitefly problems within Europe. It also provides a unique forum for disseminating information on European whitefly problems and research activities to academia and industry worldwide. With thanks to our sponsors, we have been able to increase the quality frequency and volume of EWSN’s outputs. Our regular newsletters for example, are now sent to almost one and a half thousand addresses worldwide every 2 months and an interactive website is presently being developed (www.jic.bbsrc.ac.uk/hosting/eu/ewsn).

EWSN also provides the coordinators with the ability to assemble a team of scientists whenever necessary, to travel and assess new whitefly related problems within Europe, and where possible provide advice on their control. For example, during November 1999, with the support of the BBSRC and Bayer, 18 members of EWSN carried out a comprehensive survey of agricultural regions within Tenerife and Gran Canaria, where growers were reporting the appearance of viruses in their crops for the first time.

Through a series of meetings throughout the islands, participants were able to meet growers and cooperative staff, and discuss the new agricultural problems. They were then able to visit affected crops and collect samples of whiteflies and viruses which were then analysed on return to the delegate’s respective laboratories. The findings, which included first reports of new viruses on the islands, were presented in a report that has recently been distributed within EWSN and to the growers and cooperatives on the islands. This included confirmation of CYSDV on Tenerife and a new tomato virus, Tomato chlorosis closterovirus (ToCV), which is transmitted by both B. tabaci and T. vaporariorum, on Tenerife and Gran Canaria. ToCV has also recently been found in southern Spain as well.

The Canary Island trip along with others that have been undertaken within the agricultural regions of southern Europe identified a number of very important facts regarding the present whitefly problems:

Firstly, it is essential that if whiteflies and their associated problems are to be controlled successfully, then growers must be provided with information and accurate advice on minimising whitefly ingressions and managing insecticide usage. Secondly, a failure to understand the following facts about whitefly-transmitted viruses can often lead to further problems:

  • Viruses are often transmitted rapidly and very efficiently where, in the case of Tomato yellow leaf curl viruses, a single infected whitefly has a 60% chance of transmitting the virus to a healthy plant. Under these situations, serious limitations are put on the use of biological control, since whitefly thresholds would certainly remain too high to prevent further transmission.
  • Insecticides may reduce virus spread within a crop, but rarely prevent infected whiteflies from bringing a pathogen into a crop. Studies have shown that before infected whiteflies are disabled by prophylactic treatments, they often feed and successfully inoculate the virus. Also, these viruses are acquired by whitefly larval stages, enabling already infectious adults to emerge from the protected environment of the puparium stage.
  • Virus symptoms usually appear on infected plants 2 weeks after they have been inoculated. These symptoms are often regarded as a sign of whitefly infestation and prompt additional spraying, even when whiteflies themselves, are no longer a problem to the crop. Tomato rarely hosts a large population of B. tabaci, so without virus problems, minimal control measures would be needed.
  • An overuse of insecticide can lead to resistance. The process of spraying insecticides can also serve as a means to disturb and disperse whiteflies and the viruses onto other plants. Unless managed carefully, whitefly-transmitted viruses on one crop can rapidly increase the potential for serious control problems on others.

In summary, a major factor for reducing the present virus problems, centres on halting the movement of whiteflies within and between crops and addressing the complexity of reasons behind the present epidemics. It is possible that by providing growers with the necessary information to recognise and deal with developing problems at an early stage, that the present whitefly situation in southern Spain could be dramatically improved. Training courses and information packs for growers could, with financial backing, be organised through the European Whitefly Studies Network These would provide guidelines for the early recognition of virus infected plants and weed reservoirs, as well as advice on reducing whitefly movements within and between crops, and managing an insecticide program that reduces the risks of insecticide resistance problems. The possibility also exists to establish ‘model’ greenhouses within problem areas that demonstrate the effectiveness of nettings and trap plants in reducing whitefly problems. This information would also be made available to growers within other parts of Europe where whiteflies are increasingly becoming more difficult to control within traditional growing systems.

Further information on the activities of the European Whitefly Studies Network can be obtained from the EWSN office, John Innes Centre, Colney Lane, Norwich, UK.

Whitefly Status in Latin America

by Dr. Luko Hilje (Unidad de Fitoprotección, CATIE. Turrialba, Costa Rica)

Since the mid 1980's, some 18 crops in Latin America have been affected by Bemisia tabaci (and B. argentifolii). Even though there have been cases of direct damage in crops like cotton, melons and soybean, the bulk of situations refer to transmission of geminiviruses, especially in food crops such as beans, tomato and bell pepper. The number of whitefly biotypes (at least three), wild host species (some 54) and types of viruses (at least 17 in tomatoes alone), as well as the kinds of interactions between them (which are favored by suitable year-round temperature and humidity regimes), make it difficult to deal with this problem.

Historically, this problem followed an uneven pattern, in geographical terms. It started in Central America and the Caribbean, appearing in an almost simultaneous pattern from 1986 to 1991. Later on, it affected Mexico, Venezuela, Ecuador, Colombia and Argentina, and in the last two years it has extended to Peru and Brasil. Economic losses, although not properly assessed so far, have been really high, causing a serious crisis in many countries. In response to this, in the early 1990´s, task forces at the local, regional or national levels were appointed. They drafted work plans and set up priorities on: whitefly bioecology and geminivirus epidemiology; biotype and geminivirus diagnosis; management tactics (cultural practices, host-plant resistance, biological control, chemical control and insecticide resistance management); training of extension agents and growers; and on-farm validation and transfer of IPM tactics.

In addition, an international network (Action Plan for Whitefly and Geminivirus Management in Latin America and the Caribbean) was created in 1992, in order to set research and extension agendas aimed at the development and implementation of integrated pest management (IPM) approaches. This network, which currently involves 18 countries, is coordinated by CATIE (a regional agricultural institution). Their members meet once a year to exchange information and review the status of the Action Plan. In addition, a quarterly newsletter (Whitefly Update), which now is available by Internet, is widely distributed. (See section at printed and on-line magazine Revista Manejo Integrado de Plagas).

So far, accomplishments between countries have been rather uneven. Nonetheless, growers are now better aware of the implications of the problem in economic, agricultural and environmental terms, and thus are more prone to adopt and implement IPM programs. They understand the need to look for multi-tactic approaches instead of a single-tactic, and in some cases are willing to participate in area-wide preventative and curative approaches, which involve quarantine regulations and cultural practices such as planting dates and host-free periods. In spite of these advances, there is still a pressing need to increase coverage of successful IPM programs, especially by involving growers through participatory research, in order to strengthen adoption and implementation of such programs.

Morphological, Molecular and Taxonomic Perspectives on Encarsia (Hymenoptera: Aphelinidae)

J. Heraty (Department of Entomology, University of California)

The genus Encarsia (Hymenoptera: Aphelinidae) is a diverse and cosmopolitan group of species usually parasitic on whiteflies, armored scales, or themselves (autoparasitoids). At present there are more than 200 described species(Woolley & Heraty 1999). Encarsia are one of the most important parasitic groups being exploited in biological control, and various species are currently being collected as part of foreign exploration efforts to search for biological control agents. Several species have demonstrated their importance for control of San Jose Scale (E. perniciosi), Greenhouse whitefly (E. formosa), ash whitefly (E. inaron), and citrus whitefly (E. lahorensis). New programs are focusing on the control of Bemisia with E. protransvena and E. sophia (=transvena), and on citrus whitefly in California with E. variegata. Biological and taxonomic characteristics remain poorly known even for common species of Encarsia. In this brief article, I will focus on taxonomic studies of Encarsia over the last five years, and hint at the implications of these programs for biological control.

Many species of Encarsia are undescribed. However, we must be able to accurately recognize species with the greatest potential for control. A common assumption is that closely related species may share similar habits and host preferences to known species and are therefore desirable candidates for biological control. These relationships are most commonly determined by the presence of shared derived morphological characters. Unfortunately, species groups of Encarsia, which are our first approximation of related species, are often defined by combinations of characters, many of which are characteristic of one or more species placed in other species groups. Even obvious group characteristics are found in unrelated groups of species; for example, the close placement of scutellar sensilla, which were considered diagnostic of the strenua -group, are now known to be convergent and found in several very unrelated groups of species (Heraty & Polaszek 2000).

Understanding the species groups of Encarsia is of primary importance, Currently, species are grouped arbitrarily on the basis of overall similarity. This can lead to misconceptions about behavior and host associations that are crucial for biological control programs. Analysis of morphological characters has led to differing opinions as to the relationships, composition and placement of species into groups of Encarsia (Hayat 1998; Huang & Polaszek 1999).

Beyond morphology, molecular systematics (comparing species based on their genetic similarities) offers a new character system. For separating closely related species, restriction site analysis can be used to accurately separate species of E. formosa and E. luteola, which are otherwise difficult to separate using morphological characters alone (Babcock & Heraty 2000). This provides novel ways to separating species in lab and field situations, and also a means of separating different life stages for biological studies. Although severely limited by the number of taxa that can be sampled, the analysis of nucleotide sequences can be used to test the relationships of existing groups and, perhaps more importantly, evaluate the morphological characters used to define those groups (Babcock et al. submitted). This latter point is probably the most relevant for sorting field collected material in biological control programs.

In a preliminary study of relationships in Encarsia, nuclear sequences of the D2 expansion region of 28S rDNA were determined from 67 strains of 24 species representing 10 species groups of Encarsia, two strains of Encarsiella noyesi Hayat, and one strain of Coccophagoides fuscipennis Girault (Babcock et al. submitted). Separate and combined analyses of molecular and morphological data provide support for many nodes not resolved by morphology alone, and offer insights into which morphological characters are useful for supporting group relationships. A single preferred hypothesis of relationships was obtained from the analysis of combined data, but Encarsia had to be constrained as monophyletic (cf. http://cache.ucr.edu/~heraty/Aphelinidae. html). The inaron, luteola and strenua species groups are supported as monophyletic, whereas the aurantii and parvella species groups are not. The four-segmented midtarsus, often considered to be a convergent character (Hayat 1998), was not and supported a single lineage of diverse species (cubensis + luteola groups). Another trivial character, presence of a specialized seta at the apex of the costal cell, defines a single lineage, the strenua group. In general, traditional species recognized by morphological characters were supported by the molecular data. Shifts to parasitism of Diaspididae and transformation to parthenogenesis appear to have occurred multiple times.

Basic taxonomic studies are by no means passe. Encarsia is one of the most diverse and economically important group of parasitoids. New identification keys are paramount in our ability to recognize species (Schauff et al. 1996, Hayat 1998, Huang & Polaszek 1998). New species continue to be described (Evans 1997, Evans & Polaszek 1997, Evans & Castillo 1998, Hayat 1998, Huang & Polaszek 1999, Heraty & Polaszek 2000). Several recent taxonomic changes affect the species attacking Bemisia in the southern U.S.: E. bimaculata is a new species specific to Bemisia (originally imported from India), E. transvena is now E. sophia (a species described first by Girault in 1913 in Australia), and what was regarded as E. strenua in the U.S. and Caribbean is now E. protransvena (a species described by Viggiani from Florida; E. strenua exists but occurs almost exclusively in the Orient on different genera of whiteflies). Although sometimes frustrating, these name changes will provide stability in our interpretation of species. It also emphasizes the importance of depositng voucher material; what is a relevant species today may change tommorrow and vouchers provide the necessary reference for earlier biological or ecologial studies.

Morphological studies of Encarsia have been provided from a number of sources, but exemplary awards within the United States have been provided by the USDA, National Biological Control Institute (postdoctoral fellowships to Schauff, Evans and Heraty in three separate awards, and a facilities grant for cataloging to Woolley and Heraty), California Department of Food and Agriculture for work on the strenua group, and the California Citrus Growers for studies in molecular systematics. These funds promote productivity and thus advance our knowledge of this group. Unfortunately we are still only dealing with about 243 species in a group that is likely to be megadiverse. Noyes (1990), in a single canopy insecticide-fogging sample in Sulawesi recorded more than 156 morphospecies of Encarsia! How many of these or other undescribed Encarsia have potential as biological control agents? To address these problems, we need, of course, continued funding, but to complete the circle of information we also need continued support by the field biologists who continue to supply material and the biological information we need to understand this complex group.

References (emphasizing studies of Encarsia over last five years)

  • Babcock, C. S., and Heraty, J. M. (2000). Molecular markers distinguishing Encarsia formosa Gahan and Encarsia luteola Howard (Hymenoptera: Aphelinidae). Ann. Entomol. Soc. Am. 93: (in press).

  • Babcock, C. S. , Heraty, J. M., De Barro, P. J., Driver, F. and Schmidt, S. (submitted) Preliminary phylogeny of Encarsia Förster (Hymenoptera: Aphelinidae) based on morphology and 28S rDNA. Molecul. Phylo. Evolut.

  • Evans, G. E. (1997). A new Encarsia (Hymenoptera: Aphelinidae) species reared from the Bemisia tabaci complex (Homoptera: Aleyrodidae). Florida Entomol. 80: 24-27.

  • Evans, G. A., and Castillo, J. A. (1998). Parasites of Aleurotrachelus socialis (Homoptera: Aleyrodidae) from Colombia including descriptions of two new species (Hymenoptera: Aphelinidae: Platygasteridae). Florida Entomol. 81: 171-178.

  • Evans, G. A., and Polaszek, A. (1997). Additions to the Encarsia parasitoids (Hym.: Aphelinidae) from Costa Rica. Florida Entomol. 79: 582-586.

  • Evans, G. E., and Polaszek, A. P. (1998). The Encarsia cubensis species-group (Hymenoptera: Aphelinidae). Proc. Entomol. Soc. Wash. 100: 222-233.

  • Hayat, M. (1998). Aphelinidae of India (Hymenoptera: Chalcidoidea): A taxonomic revision. Mem. Entomol. Intern. 13: 416 pp.

  • Heraty, J. M. and Polaszek, A. (2000). Morphometric analysis and descriptions of selected species in the Encarsia strenua group (Hymenoptera: Aphelinidae). J. Hymen. Res. 9: 142-169.

  • Huang, J., and Polaszek, A. (1998). A revision of the Chinese species of Encarsia Förster (Hymenoptera: Aphelinidae): parasitoids of whiteflies, scale insects and aphids (Hemiptera: Aleyrodidae, Diaspididae, Aphidoidea). J. Nat. Hist. 32: 1825-1966.

  • Noyes, J.S. (1989). The diversity of Hymenoptera in the tropics with special reference to Parasitica in Sulawesi. Ecol. Entomol. 14: 197-207.

  • Schauff, M. E., Evans, G. A., and Heraty, J. M. (1996). A pictorial guide to the species of Encarsia (Hymenoptera: Aphelinidae) parasitic on whiteflies (Homoptera: Aleyrodidae) in North America. Proc. Entomol. Soc. Wash. 98: 1-35.

  • Woolley, J.M. And J.M. Heraty. 1998. Encarsia species of the world: A searchable database. [a catalogue of about 313 species of Encarsia with information on types, distribution and hosts]

  • World Distribution of Parasitoids of Bemisia tabaci Group. D. Gerling is developing a listing of known parasitoids of the B. tabaci group, and their distributions. For comments, please contact Dan.

Meetings

Action Plan for the Management of Whiteflies and Geminivirus in Latin America and the Caribbean
This includes the following countries: Mexico, Guatemala, Belize, El Salvador, Honduras, Nicaragua, Costa Rica, Panama, Dominican Republic, Cuba, Puerto Rico, Haiti, Venezuela, Colombia, Ecuador, Brazil, Peru and Argentina. The advances of the Action Plan, between 1998-1999, were presented, in the VIII Workshop, which took place in October of 1999 in Recife, Brazil. Three hundred and fifteen people were present form 13 countries (including Spain, U.S.A. and Israel) and 15 Brazilian states, including researchers, lecturers, extensionists, students, agricultural producers, and technicians from the private sector (agrochemical companies and banks). Furthermore, as well as a large number of poster presentations (89), there were magisterial talks by researchers of world significance, as well as panels with different focuses (countries, crops and current topics). The 2000 workshop will take place in Panama and that of 2001, in Cuba. Those interested should contact Luko Hilje.

The XXI Congress of Entomology
A full day symposium on Bemisia will be held in the XXI Congress of Entomology, August 2000, in Brazil. The program will be as follows:

  • Challenges and Opportunities for Pest Management of Bemisia in the New Century
    Organizers: Steven E. Naranjo, Maria R. V. Oliveira, Peter C. Ellsworth, Odair A. Fernandes

  • MORNING SESSION (Sponsored by Session 14: IPM)
    • Introduction to Morning Session of Symposium, Odair A. Fernandes
    • History and Current Status of Bemisia, Maria Regina Vilarinho Oliveira, Thomas Henneberry & Raul Leon-Lopez
    • The Bemisia Species Complex: A Challenging Systematic Issue, Thomas Perring
    • Overview of Insecticidal Control and Resistance Management, John Palumbo, Rami Horowitz & Nilima Prabhaker
    • Biological Control with Predators and Parasitoids, Dan Gerling & Oscar Alomar
    • Biological Control with Fungi, Marcos Faria, Lance Osborne, Zdenek Landa & Ceske Budejovic
    • Cultural Practices for Managing Whiteflies, Phil A. Stansly, Luko Hilje & Heather Costa

  • AFTERNOON SESSION (Sponsored by Session 2: Agricultural Entomology)
    • Introduction to Afternoon Session, Maria Regina Vilarinho Oliveira
    • Host Plant Resistance for Bemisia tabaci other Whitefly Species, and Associated Viruses, Anthony Bellotti & Francisco Morales
    • Ecological Considerations for Management of Multiple-Crop Pests, Peter Ellsworth, John C. Palumbo, Steven E. Naranjo & Steven J. Castle
    • Conservation and Evaluation of Natural Enemies in IPM Systems, Steve Naranjo & Walker Jones
    • International and National Research Programs for the Development of IPM Systems, Pamela Anderson, Tom Henneberry & Maria Regina Vilarinho Oliveira
    • IPM of Bemisia tabaci in Australasia, Paul De Barro, Felice Driver, Ian Naumann, Stefan Schmidt, John Trueman & John Curran
    • Implementation and Adoption of IPM Systems, Jose L. Martinez-Carrillo, Reuben Ausher, Peter Ellsworth, Luko Hilje, & Reuben Ausher.

The Third International Workshop on Bemisia

The Third International Bemisia Workshop was scheduled to take place in July 2001 at the John Innes Institute, in conjunction with the meeting of the Geminivirus Workgroup. However, due to the forthcoming symposium sponsored by EWSN (see below), it was decided to postpone the workshop. No date has been set as yet, and members of the International Bemisia Workgroup and colleagues are invited to offer their suggestions as to the date and place best suitable. Meanwhile, although the EWSN meeting will cover all whiteflies and all aspects of whitefly in Europe, the major thrust will concern Bemisia. Thus, we are confident that the exchange of facts that will take place in that meeting will contribute measurably to the exchange of information and fostering of ideas concerning Bemisia research.

European Whitefly Symposium

The European Whitefly Studies Network (EWSN: a Concerted Action funded by the European Union FAIR 6 CT98-4303), is organising an international whitefly symposium at the University of Catania, Faculty of Agriculture, Ragusa, Sicily (Italy) from February 28th to March 3rd, 2001. This symposium will address the following whitefly-related disciplines:

    1. Virology
    2. Pest and Disease Epidemiology
    3. Faunistics and Systematics
    4. Natural Enemies
    5. Plant Protection/Integrated Pest Management

The majority of delegates will comprise EWSN members and local personnel active in whitefly research and management. Presentations will be given by these delegates and also a small number of invited international speakers. The symposium is already attracting a high level of interest and persons wishing to attend are advised that the number of delegates is likely to be strictly limited. Registrations should be made as soon as possible by contacting the EWSN research facilitator: Mr. David Oliver at
John Innes Centre.

Whitefly E-Mail Exchange Group

If you have e-mail access, you can send and receive information among a large group of whitefly workers by joining the Whitefly Listserver. To automatically join, send a message with no Subject to:

listserv@listserv.tamu.edu

In the body, type subscribe. To get off the network, type the message unsubscribe to the same address above.

After getting subscribed, messages to the group must be sent to a different address:

whitefly-l@tamu.edu

For friendly help, contact Reyes Garcia III, Whitefly Net Administrator

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