Keywords: business services, economic decentralization, polycentricity, spatial differentiation, labor market sub-fragmentation

What is the importance of business services decentralization in a Parisian metropolitan region known for its inherited monocentricity? Using revised statistical and cartographic methodological tools, I try to answer two debates: Is the new Parisian metropolitan economic geography one of dispersal or of polycentricity? Does decentralization mean the decline or the reinforcement of the economic core? If secondary suburban economic centers benefit from business services decentralization trends, Paris City's neighboring spaces such as the Inner western suburbs of La Défense and Boulogne-Billancourt are affected too. This paper intends to demonstrate that polycentricity is not opposite to the constitution of a new golden triangle within the dense part of the agglomeration.

This means both that economic centrality still matters (thus questioning that dispersed cities is the twenty-first century's metropolitan archetype), and that an enlarged CBD (Core Business District) straddling Paris and the western Hauts-de-Seine département, is being reinforced (thus invalidating CBD decline theory).

Thanks to the widening of the business district from Paris to La Défense, the labor market remains an integrated one; meanwhile, secondary economic centers in the Outer Suburbs tend to create fragmented sub-regional labor markets of their own.

Introduction

Business services location is going through a mutation at both the international and intra-metropolitan levels. From Peter Hall's world cities in the 1960s [START_REF] Hall | The world cities[END_REF]) to Sassen's "global city" [START_REF] Sassen | The global city[END_REF], research on worldwide metropolitan regions has been blossoming. According to Sassen, globalization dynamics, is characterized by both an increasing importance of international exchanges (including financial flows) and a reorganization in corporate strategies in order to access this world market, has led to the constitution of particular metropolitan regions such as London, New York, and Tokyo. These regions are all characterized by the importance of financial and service producers' activities which have therefore been taken as indicators of the globalization degree of cities. The more important the share of service producers, the more global a city is. In this regard, Paris has been the focus of a debate that is still ongoing. Sassen included it in her list of global cities while some specificities of the Paris metropolitan region still seem to contradict such a choice (see [START_REF] Sassen | The global city[END_REF]. Going past this "global city" argument, [START_REF] Veltz | Mondialisation, villes et territoire: L'économie d'archipel[END_REF] work has established how the Paris region belongs to what he calls an "archipelagic economy" which tends to associate key economic regions in a global network.

Such a network has been studied recently by the Loughborough Group Analysis of World Cities (GaWC) (see [START_REF] Taylor | World city network. A global urban analysis[END_REF]and on London's case, Beaverstock, Smith, and Taylor 2003), which illustrates how the strategies of multinational firms rely on specific nodes embodied by some major urban regions; in this ranking, Paris comes second in Western Europe, just after London. Daniels's work point out how the dynamics observed at the international level are linked to the reconfiguration of the intra-metropolitan geography [START_REF] Daniels | Service industries in the world economy[END_REF].

As early as the 1960s, Gottmann focused on the intra-regional level with his analysis of the Megalopolis. The French geographer depicted a multicentered urban organization stretching from Boston to Washington where the strongly interrelated economic centers where benefiting from functional and spatial division of the productive system [START_REF] Gottmann | Megalopolis: The urbanized northeastern seaboard of the United States[END_REF]. Since then, urban and economic geographers have endeavoured to document the reorganization of productive systems as secondary economic centers have grown in often traditionally monocentric city-regions. In the case of North American metropolitan regions for instance, the suburbanization of service producers has been theorized by the terminology of "third wave" decentralization [START_REF] Cervero | America's suburban centers[END_REF]; that is, business services tend to leave the historical Core Business District (CBD) for more attractive peripheral suburban places and, in so doing, following the earlier departure of population, manufacturing, and household services. However, if the existence of this dynamic is well recognized in the scientific community, it raises two geographical debates that are still unsettled; namely, whether the new Parisian metropolitan economic geography is one of dispersal or of polycentricity and whether decentralization means the decline or the reinforcement of the economic core. This paper will address these debates by looking at the case of the Paris region.

Reevaluating Business Services Deconcentration

At the outset, the importance of business services decentralization in reshaping the economic geography of cities must be evaluated. The North American CBD-centered urban agglomeration is sometimes described as a form of the past. The "corporate exodus" observed in the case of New York for instance has led some authors to predict the death of cities [START_REF] Jacobs | The death and life of great American cities[END_REF]. In this context, what new spatial patterns do metropolitan regions adopt? The Californian examples of Silicon Valley and Orange County [START_REF] Gordon | The distribution of population and employment in a polycentric city: The case of Los Angeles[END_REF]Richardson 1986, 1996a) demonstrate the constitution of dispersed urban regions where CBDs' tend to be small, as if unable to compete with vast fastgrowing suburban areas. Other case studies show that spatially limited suburban economic centers, known as "edge cities" [START_REF] Garreau | The edge city: Life on a new frontier[END_REF], are emerging on peripheral areas, creating polycentric metropolitan regions. This geographical debate questions the meaning of centrality. If "edge cities" are still economic concentrations, even if on the outskirts of urban agglomerations, dispersion trends signify on the contrary the end of "economic centrality" as large, noncentered sub-regions are being constituted.

Secondly, the interpretation of decentralization processes is puzzling. Some U.S. authors argue that it is a proof of CBD decline (for instance, [START_REF] Garreau | The edge city: Life on a new frontier[END_REF]. According to them, traditional business districts have become less efficient places, unable to compete in the global economic system: their office market is said not only to be inadequate and too expensive but also to suffer the consequences of a negative image due to traffic congestion and social tensions.

Against this perspective, some Canadian researchers argue the CBD is in fact being reinforced (Coffey and Polèse 1996). If major Canadian urban regions face the business services decentralization trends, this process cannot be explained by factors that are identified as being specific to U.S. cities as is illustrated in the case of Montreal [START_REF] Coffey | The intrametropolitan location of high order services: Patterns, factors, and mobility in Montreal[END_REF]. Business services departure expresses rather the selective consolidation of the traditional CBD that manages to send away in peripheral locations low value-added services, and hence to keep concentrating high-order activities, thanks to expensive office markets.

The strengthening of the competition for central location is not to be taken for granted. As Information and Computer Technologies (ICT) and telecommunications develop and as transport costs decrease, one could think that location does not matter as much as it used to [START_REF] Cairncross | The death of distance: How the communications revolution will change our lives[END_REF]. Indeed, to locate a firm in the periphery of a major metropolitan region is a way both to benefit from agglomeration and size economies and to reduce central location diseconomies. In other words, it allows companies to be closer to the workforce and to cut down real estate costs while still being strongly connected to the central economic center, and to major national and international gateways such as airports, railway stations, and highways.

However, the literature insists that centripetal forces work against decentralization processes. Changes in the global economy as well as firms reorganizations have been used to explain that. In an internationalized economy, a firm must find the balance between the global and the local scale (the term "glocalization" has sometimes been used). Corporate strategies are looking for an equilibrium between the necessity to centralize decisions in order to increase efficiency and productivity gains, while still being decentralized enough to be reactive with the specificities of regional markets. Hence, the constitution of a multilayered network of world cities which are part of a hierarchical international urban system. For some authors, the logic underlying this decentralization of multinational firms relies on the necessity to be in contact with clients and partners as one of the specificity of the service sector is the involvement of the consumer during the production process [START_REF] Bonamy | Services et mutations urbaines[END_REF]. Consequently, the development of ICTs induces that nonstandardized information which can only be collected through face-to-face contact becomes always more strategic [START_REF] Graham | Telecommunications and the city: Electronic spaces, urban places[END_REF][START_REF] Castells | The rise of the network society[END_REF]. Therefore, the closer the service producers are to their clients, the more productive the organization. In the French consulting industries, the numerous openings of secondary offices in Lyon, Lille, Toulouse, or Marseille during the 1990s from Paris-based headquarters express this necessity. Transposed at the intra-metropolitan level, the face-to-face requirement pleads in favor of the most central locations in the city-region. However, in the Paris region, this factor must be balanced by public planning policies. Indeed, the regional Schémas Directeurs (Guiding Schemes) have been trying to develop a more polycentric urban organization based on a network of Villes Nouvelles (New Towns) and on public investments in railway and road transport infrastructures. The effects could promote the decentralization of activities.

Paris, a Test Metropolitan Region

The above-mentioned debates on the intra-metropolitan reconfiguration of main cities in the world have led to many case studies. To name but a few, Sydney, Copenhagen, or London urban regions have been the focus of research teams. Quite interestingly, the Sydney study [START_REF] Pfister | Polycentricity or dispersion? Changes in center employment in metropolitan Sydney (1981<<nut>>1996)[END_REF] has shown how deconcentration trends were effective in a metropolitan region which is one of low density and long distances. Being far away from the main economic center seems to make it easier for a secondary economic center to develop. In Copenhagen's case [START_REF] Illeris | The changing location of service activities in the Copenhagen region[END_REF], the study of advanced business producers attested to the reality of decentralization trends by showing how a large sub-regional quadrant benefited from such dynamics, especially in ICT industries.

Hall proposed to generalize the results he observed in London to a set of Western European metropolitan regions (see the introduction to the [2003][2004][2005][2006] Interreg IIIb POLYNET project): rejecting the North America-based model of edge cities which does not seem to be efficient to depict old historical cities that have been rebuilding on themselves rather than expanding indefinitely (see [START_REF] Cattan | Le système des villes européennes[END_REF][START_REF] Huet | Une génétique urbaine[END_REF]), he argues that decentralization in the cases of London, Randstad, Rhine-Rhur, Rhine-Main, and Brussels regions may be characterized by a "concentrated deconcentration." The decentralization of the metropolitan economic core benefits mostly secondary economic poles of the metropolitan region. In this context, studies of the Paris region are not numerous, as urban and economic geographers have often been reluctant to undertake analysis of a metropolis described as unchangingly monocentric.

It is true that the Paris region area is denser and more compact than common world cities (such as London for instance). Even if suburbanization processes are long historical ones, some of which can be dated as early as in the second half of the nineteenth century, no suburb stretches on over endless distances. If the Paris administrative region (Ile-de-France) is 12,000 km²that is to say as big as the London metropolitan area (IAURIF, 2002)-however, only 20 percent of it is urban. With such a small size and a high density (the regional 900 inhabitants per km average in effect hides a much more important urban density in the agglomeration), the Paris region is unlikely to develop business services decentralization trends. This is explained by the fact that the development of secondary economic centers in the agglomeration requires competition against an historically predominant central core that is only a few kilometers away.

Moreover, as the political, economic, and cultural capital of France, Paris is not only the first metropolitan area in a macrocephalic urban system (Paris is seven times the size of Lyon, the second largest French city), it also concentrates many national-level activities. State government, national, and multinational headquarters as well as cultural centers have long been located within the 105 km² of the City of Paris. These very reasons make the study of the business services decentralization hypothesis through the Paris case even more relevant since this metropolitan region seems resistant enough to test the intensity of the processes of suburbanization of business services. Indeed, Beckouche's work (1999;[START_REF] Beckouche | Géographie économique de la région parisienne[END_REF] during the 1990s demonstrates how the western districts (arrondissements) of Paris were no longer the only economic concentration as the business district La Défense, for instance, was gaining in importance. [START_REF] Alvergne | Intrametropolitan patterns of high-order business service location: A comparative study of seventeen sectors in Ilede-France[END_REF] proposed a detailed study of employment by business services. They observed a decentralization trend characterized between diffusion and concentration logics. Nevertheless, their approach does not go beyond the economic sector analysis and does not interrogate the spatial division of labor within the region.

Business Services Decentralization in the Paris Region: A Complex Spatial Reorganization

Against this background, I will analyze, in the remainder of this paper, the geography of business services not only by measuring the importance of decentralization trends, but also their consequences on the relationships between the main economic core and other secondary centers, as well as on the regional labor market geography. As decentralization trends occur, is the spatial division of labor getting more intense? Moreover, what is the role played by the traditional center: is it still the decisional core of the metropolis? What about new developing secondary economic centers: are they merely obeying central orders coming from the core or attracting more up-market activities? Finally, what is the nature of the relationship between economic centers: indifference, competition, co-operation? The Paris region used to be praised for its relative integration in one single metropolitan labor market [START_REF] Rousseau | Structure spatiale et efficacité économique. Une comparaison de la région parisienne et de la région londonienne[END_REF]. Is sub-regional fragmentation, such as it is described in some of North American urban regions [START_REF] Godfrey | Restructuring and decentralization in a world city[END_REF], occurring there as well?

The scale of analysis obviously matters in the understanding of metropolitan economic geography's transformations. Against the use of what seems to be too wide a spatial aggregate in some North American studies (mainly because of the nature of available data), I will not only map economic data at the broad scale of metropolitan areas, i.e., the city and its two peripheral rings, but also at much finer levels. The use of different scales allows us to go beyond a mere center/periphery approach, as most authors aspire to (see the recommendations of Gordon and Richardson 1996b, and to provide new insights on the complex reorganization that affects metropolitan economic geographies.

Indeed the use of municipality level-based maps allows a more precise depiction of economic geography's transformations.

Moving Off Center: A Center/Periphery Analysis

The most common methodological approach to study job decentralization is the center/periphery analysis. To name but one major contribution, Gordon and Richardson's article (1996b) reached the conclusion that Los Angeles represented the norm rather than an outlier of decentralized urban region thanks to a scientific protocol that compared population and employment geography between three areas defined as the Core City, the Primary Metropolitan Statistical Area, and the rest of the Consolidated Metropolitan Statistical Area.

This represents the easiest way to study decentralization trends as most of the available data are given at this broad metropolitan scale.

To ensure comparability, I use the same methodological approach by defining three study areas: Paris City, the first metropolitan area referred to as Inner Suburbs (Petite Couronne), and a second larger one which I will refer to as the Outer Suburbs (Grande Couronne) (Figure 1). In order to track the changing localization of service sector activities, I use employment statistics given by the Insee (the French equivalent of the National Bureau of the Census) on the three last censuses (1982, 1990, and 1999). I will analyze all activities that can be defined as producing services mainly sold to firms. These belong to what has been called the "peri-productive" sector in the Strates' team analytical grid [START_REF] Beckouche | Une grille d'analyse globale de l'emploi[END_REF]. Three main types of economic sectors are involved in this category: Business Services (such as management, marketing, accounting, legal affairs, IT, real estate, and R&D), Banking-Finance-Insurance, and Transport and Telecommunications industries. These jobs account for over 40 percent of total employment in the Ile-de-France region with a figure of around 1.85 million in 1999. The number has known an overall increase since 1982 (2.3 percent per year) with more than 640,000 new jobs, even though the first inter-census period of 1982 to 1990 shows a stronger growth than the second (1990 to 1999). The localization of producer services activities is more or less equally shared between Paris and its two suburban rings (Figure 2). With a figure of 485,000 producer services jobs, the Outer Suburbs are only slightly under the 635,000 and 700,000 of respectively Paris City and the Inner Suburbs.

In an inherited monocentric agglomeration, this situation can only be explained by an intense spatial reorganization of the productive system.

Over the 1982 to 1999 period, if the overall growth of peri-productive jobs has been strong, it was however unequally distributed. Paris City for instance, the traditional producer services employment center of the metropolitan region did not benefit from this positive trend, finding it hard on the contrary to stabilize its own figure (-0.3 percent per year). Meanwhile, the rest of the region has known a steady expansion. The Inner Suburbs gained 300,000 producer services jobs with a variation of +4.5 percent per year, enabling it to become more important in size than Paris City. The Outer Suburbs showed the highest variation rate over the period with +6.1 percent per year, that is to say a net gain of 247,000 peri-productive jobs. These figures recall North American authors' observations: there is a metropolitan decentralization gradient that benefits most "peripheral" areas.

A More Complex Geographic Pattern.

This description however is too simplistic: the center/periphery gradient is not sufficient to explain mutations in the metropolitan economic system. By changing the scale of observation, the decentralization processes appear more complex. To demonstrate this, I focus on statistical data at the départemental level. The Ile-de-France region is subdivided into 8 départements (equivalent of counties). Paris is a département by itself whereas the Inner Suburbs includes three of them (the Hauts-de-Seine, west of Paris, the Seine-Saint-Denis on the northeast, and the Val de Marne on the southeast), and the Outer Suburbs have four (the northwestern Val d'Oise, the northeastern and eastern Seine-et-Marne, the Essonne on the south part, and the southwestern Yvelines département) (Figure 1). In 1999, départemental figures show a distribution of producer services employment still dominated by Paris (Figure 3). The only département able to compete with the French capital is the Hauts-de-Seine with 368,000 producer services jobs (20.2 percent of the regional total). The six other départements are far behind, their producer services employment ranging from 100,000 to 180,000 jobs, that is to say from 5 percent to 10 percent of Ile-de-France's total. This indicates that the actual center of the metropolitan economy in 1999 is no longer Paris alone but the two départements of Paris and the Hauts-de-Seine. Somehow, the regional economic core has been enlarged to the first Western Inner Suburbs.

The départemental variation between 1982 and 1999 allows more subtle observations (Figure 4). If the four Outer Suburbs départements benefit from a steady growth (between +5.3 and +7.3 percent per year), thus confirming decentralization processes, the situation in the Inner Suburbs is much more unequal. Trends are utterly different between Val-de-Marne and Seine-Saint-Denis départements, where variation over the same period only slightly exceeds the regional average with +3 percent per year, and the Hauts-de-Seine's spectacular growth (+6.2 percent per year). This confirms an imbalanced growth pattern in the center of the agglomeration between a fast growing western half and a slower developing eastern part. Consequently, the départemental approach testifies that observations made at a simple center/periphery level do not allow any definitive conclusions. Slightly changing the scale of analysis gives another understanding of the productive system's geography. In this case, the decline of the center against fast growing suburbs asserted by a center/periphery model is challenged by a view where Outer Suburbs' strong development is not opposite to the enlargement of the economic center from Paris to the Hauts-de-Seine département. The most precise spatial aggregate given by the Insee is that of the municipalities (communes in French). With over 1,300 of them in the Paris region, it allows the drawing of an accurate cartography of producer services employment. The aim is to understand the form taken by the decentralization trend. Thus, the question must be asked: Is the metropolitan region affected by dispersal dynamics producing large sub-regional producer services employment area or is it limited to a few economic centers, i.e. dispersion versus "concentrated deconcentration" theories?

In 1999, the cartography of producer services jobs showed the predominance of a triangle-shaped area centered on Paris and its adjacent western municipalities (Figure 5). The three summits of this triangle are the western arrondissements (districts) of Paris, known as the Financial City (218,000 peri-productive jobs); La Défense economic center and its neighboring municipalities, located in the middle of the Hauts-de-Seine département Meanwhile, even if not weighing as much in the Ile-de-France economic structure, "secondary economic centers" [START_REF] Cervero | America's suburban centers[END_REF]) can be identified: the 12th and 13th arrondissements on the eastern part of Paris (77,000 periproductive jobs); the two airports of Orly and Roissy (34,000 and 50,000); and the villes nouvelles (the Paris region's new towns) that are eastern Marne-la-Vallée (37,000 peri-productive jobs), southeastern Evry and Sénart (30,000), southwestern Saint-Quentin-en-Yvelines (34,000), and northwestern Cergy-Pontoise (26,000). To what extent is this description related to the last 20 years of spatial mutation of the regional economic system? Paris' business district is affected by a decline of producer services employment. Between 1982 and 1999, it lost 77,000 jobs, that is to say a decrease of over a quarter of its original size.

On a broader Parisian scale, only the eastern districts of the French capital (mainly the 12th arrondissement) have been able to keep up with the regional development pace (+3.1 percent, a gain of 27,000 jobs). Highly contrasting with this Parisian decline, the middle of the Hauts-de-Seine département area, pulled up by La Défense, shows the strongest regional variation (+7.9 percent per year, +94,000 peri-productive jobs). The southern part of the Hauts-de-Seine département is not far behind, with an additional 44,000 jobs and 17,000 jobs, respectively, for Boulogne-Billancourt/Issy-les-Moulineaux and the south Hautsde-Seine. Economic development is spreading on a spatial contiguity basis, leading to the formation of the triangle shape core straddling Paris and the Hauts-de-Seine département. If this phenomenon had been noticed by some authors before [START_REF] Beckouche | Pour une métropolisation raisonnée: Diagnostic socioéconomique de l'Ile-de-France[END_REF], it has never been demonstrated that clearly so far.

More recently, in the last decade, the spatial expansion of the Paris region CBD seems to have benefited other municipalities as if even the Hauts-de-Seine were now becoming close to being saturated. This is obvious with the two northern municipalities of Saint-Denis and Aubervilliers (9,000 peri-productive jobs gained over the 1982 to 1999 period), yet this pattern remains to be demonstrated with other municipalities surrounding Paris along the internal expressway (the "Périphérique"). However, recent data on office market geography tend to confirm such a trend [START_REF] Bertrand | Construction de bureaux 2000-2004: L'attrait de la couronne parisienne[END_REF].

Outer Suburbs face the same dramatic geographic transformation. If residential areas are hardly affected at all, two main economic trajectories can be observed. First, relatively isolated secondary economic centers are growing vigorously. They are spreading only in a few surrounding municipalities such as Roissy (+10.7 percent per year, a gain of 32,000 peri-productive jobs), Cergy (+8.1 percent per year, a gain of 15,000 jobs) or Evry (+11.9 percent per year, a gain of 13,000 jobs). In other parts of the metropolitan area, producer services corridors are being constituted. They link two or more secondary economic centers either together or to the central metropolitan triangle. Examples are in the eastern part of the region with Marne-la-Vallée (+19.8 percent per year, that is to say a gain of 29,000 peri-productive jobs) and in the south with an axis stretching from Saint-Quentin-en-Yvelines to Saclay (a cumulated gain of 50,000 peri-productive jobs). However, this last example of the constitution of an important secondary peri-productive area is nothing in comparison to the large sub-regional dispersed examples depicted in California.

Over the last 20 years then producer services employment decentralization, or more exactly the distribution of this growth, seems to favor a reorganization of the metropolitan economic geography. From a rather monocentric agglomeration under the predominance of a single Parisian business district at the beginning of the 1980s, the geography of the economic system has become one of a metropolitan region whose structure, far from being dispersed as seen in some North American cities, is rather polycentric. This confirms that central location -or at least economic centrality whether in the middle of the agglomeration or on its edges -still matters.

The Limits of Deconcentration: The City Center

Reinforcement Hypothesis

In light of the above, what are the reasons explaining the decentralization process affecting producer services jobs? Is the business district suffering a decline that benefits other areas of the metropolitan region or is this deconcentration process, on the contrary, a testimony to its increasing strength?

The answer to this question will vary depending on the indicators being looked at. The first difficulty then is to reach a scientifically shared definition of which activities embody today's economic centrality. Most authors agree on a list of business services often described as "high-order services activities" or "advanced services producers" [START_REF] Coffey | The intrametropolitan location of high order services: Patterns, factors, and mobility in Montreal[END_REF]. Behind the labels, it is however sometimes difficult to be sure either of the exact content of the data used to localize such markers of economic centrality, or of its comparability with other case studies' statistics.

I propose that a mere economic sectors analysis is not sufficient. Most of the time, high-order services are defined as a set of economic sectors such as headquarters or knowledge intensive business services (KIBS). A nonexhaustive list would have the jobs involved in management, accounting, legal affairs, finance and real estate, etc. [START_REF] Alvergne | Intrametropolitan patterns of high-order business service location: A comparative study of seventeen sectors in Ilede-France[END_REF]. But even in such sectors, as in any others, all the employees are not highly qualified professionals.

Some of the labor force, sometimes a majority of this force as described by a SIC code such as in many headquarters, is only partly qualified (clerical jobs for instance). Therefore, studies of high-order services are often biased, taking into account jobs that are not relevant to the question. To map the "advanced service producers," it is therefore necessary to go through an analysis crossing economic sectors and business functions. This is possible in the Paris case thanks to the STRATES statistical tool whose interest is in its capacity to inform every single job with two pieces of information: the economic sector which describes the main activity of the firm employing the labor force (based on the French equivalent of SIC Codes), and the professional function which details the specific activity of each employee within a firm (managerial staff, technicians, researchers, etc.). The aim of this tool is not only to go beyond a too simplistic an economic description opposing secondary and tertiary activities, such a distinction being nowadays too rough to understand the complexity of productive systems, but also to add functional information to sectoral analysis. In our case, "advanced services producers"

show the following characteristics: they belong to the economic sectors of either Production (manufacturing, building, agriculture) or Peri-production (business services, Finance-Bank-Insurance, or Transport & Telecom); they deal with functions of justice, culture, research, management, engineering, or logistics;

and they belong to the upper professional categories (highly qualified whitecollar workers).

According to the above, in 1999 the Paris region accounted for around 700,000 high-order services jobs, representing 15 percent of the regional labor Advanced Services Producers' Geography: A Central Location in 1999.

High-order services are slightly more concentrated in the geographic center of the agglomeration than the producer services economic sector. In 1999, the French capital City and the Inner Suburbs count 240,000 and 284,000 high-order services jobs, that is to say 35 and 41 percent, respectively, of the regional total.

The Outer Suburbs are lagging behind with only 24 percent of Ile-de-France region, a low figure compared to their share of a third of the total regional labor force. Location quotients calculated as the share of high-order services of the share of peri-productive employment testifies this rather more central location. If the Paris location quotient is close to 1 (indicating no particular specialization in high-order services) the Inner Suburbs value is of 1.25, outnumbering the Outer Suburbs result by 0.74.

The départemental analysis details this observation. With 28 percent of the regional high-order services employment, the Hauts-de-Seine are not far from Paris. Meanwhile the Yvelines, (the western and southwestern département of the Outer Suburbs), is twice as big as any of the remaining départements, with 70,000 high-order services jobs (10 percent of the regional total). This indicates not only the predominance of Paris and the Hauts-de-Seine (the latter department location quotient is of 1.41) as the core of the regional economic system (63 percent of Ile-de-France's high-order services jobs are in these two départements) but also the enduring nature of an east/west imbalance, the Yvelines and the Hauts-de-Seine départements representing over 60 percent of regional high-order employment outside Paris (their cumulated location quotient is of 1.69).

The cartography at the scale of municipalities gives a more precise view (Figure 6). First of all, the central metropolitan nature of high-order services is confirmed: the center of the metropolitan region is where the most important number of jobs are concentrated. Then again, we identify the golden triangle mentioned earlier with the study of peri-productive activities (Paris' business districts in the Western arrondissements, La Défense and its surroundings, linked to the French capital by the municipalities of Neuilly-sur-Seine and Levallois-Perret and the third summit of Boulogne-Billancourt/Issy-les-Moulineaux). With 361,000 high-order services jobs in 1999, that is to say over half of the regional total, it is not only the business core of the Paris metropolitan region but also its most important decision making center. On the contrary, the eastern Parisian districts and their neighboring municipalities in the north and east of the Inner Suburbs have only few high-order services jobs as if unable to compete with the center.

In the Outer suburbs, high-order services are not numerous. Yet, secondary centers and corridors can be observed: Cergy, Roissy, and Noisy-le-Grand (Marne-la-Vallée) are some examples (9,000 to 12,000 jobs each).

However, the most impressive concentration is located in the southwestern part of the metropolitan region. This is mainly the corridor linking Saint-Quentin-en-Yvelines to Vélizy-Villacoublay (33,000 high-order services jobs) and the axis between Massy and Saclay (16,000 jobs).

1982-1999: Reinforcement of the Center?

High-order services have been growing strongly in the Ile-de-France region, passing from 450,000 jobs in 1982 to 700,000 in 1999, that is to say a gain of 3.35 percent per year over the period. This variation must be compared to the global labor force evolution which shows a growth of 0.4 percent per year on the same period. In other words, high-order services have largely contributed to the overall variation in the labor force market between 1982 and 1999, its share rising from 10 percent of the regional total workforce to 15 percent. If the Inner and Outer Suburbs gained respectively 127,000 and 92,000 high-order services jobs (+4.7 percent per year and +6.7 percent per year), Paris has also benefited from this general trend with an increase of 34,000 jobs (+0.9 percent per year) (Figure 7). However, the French capital suffered a decline relatively to other metropolitan areas going from 47 percent of regional high-order services employment in 1982 to 34 percent in 1999. At first glance, one would think considering the center/periphery approach that the economic core is declining. A finer spatial analysis tends to show the contrary.

In order to measure the importance of the transformation of high-order services location within the metropolitan region, I refer to the coefficient of concentration.1 In 1999, its value is 55 for the Ile-de-France population, 88 for the whole labor force, and 171 for the high-order services jobs. This confirms that high-order services are more concentrated than the labor force, which is itself more than the population. Between 1982 and 1999, the coefficient decreases (it was 253 in 1982): high-order services employment is being distributed to a more important number of municipalities. This is however not enough to diagnose a decline of the Parisian center.

A cartographic analysis on the variation of high-order services employment between 1982 and 1999 clearly shows two distinct but still complementary trends. First of all, the places that have the most important variation in size are La Défense (+50,000 jobs) and Boulogne-Billancourt/Issy-les-Moulineaux (+25,000). The first conclusion to be drawn is therefore that Paris CBD decentralization benefits mostly the two main economic centers of the Hauts-de-Seine département. In other words, metropolitan economic centrality is not put at stake but rather enlarged. Meanwhile, this broadening of the core center is not opposite to the development of secondary economic centers in Outer Suburbs.

The southwestern part of the metropolitan region comes first: Saint-Quentin, Vélizy, Massy, and Saclay are going through an impressive variation showing the highest growth rates of the region (over 17 percent per year for some of them, that is to say a cumulated variation of +34,000 high-order services jobs). With smaller figures, it also verified in Cergy, Roissy, and Marne-la-Vallée (a gain of 6,000 to 10,000 jobs).

In conclusion, there is no such thing as a declining central core in the Paris region but instead one can observe a redistribution of its strong growth toward close neighboring western municipalities (chiefly La Défense and Boulogne), a redistribution that in fact widens its extent. This, however, does not prevent the development of secondary economic centers in the Outer Suburbs, and more specifically in the southwestern suburbs. As it follows, the renewed metropolitan economic geography is one of complex dynamics leading to a new spatial division of labor.

Towards a Dissociated Polycentricity?

In order to study the spatial division of metropolitan labor (restricted in this case to peri-productive activities), I focus, in the last section of this paper, on main employment concentrations. The methodology is based on a two-step protocol. First, thresholds to select main municipalities are defined, i.e., at least 2,600 peri-productive jobs and a density of producer services and high-order services jobs per built urban space over respectively 10 and 4: a hundred municipalities meet these criteria. Secondly, municipalities are gathered together into economic centers according to spatial contiguity criteria, economic profile likeness (economic sectors as well as functions), and identity of their recruitment area. Thanks to this method, 21 producer services economic centers are identified in the Paris metropolitan region. Only amounting to 8 percent of the region's municipalities, they represent nothing less than 62 percent of the labor force, 72 percent of Ile-de-France's peri-productive employment, and as much as 79 percent of high-order services jobs. These figures are an indicator of Paris' metropolitan polycentricity.

Differences between these economic centers are to be acknowledged according to their location within the urban region, their branch sectors and functions specializations, and the proportion of high-order services employment in their labor force. This has led us to build a typology describing the metropolitan spatial division of labor, a division that can be summarized as one of "dissociated polycentricity." This refers to the hypothesis that there is a link between economic geography's polycentric shape and the requirements of the productive system where economic sectors and functions are being partly dissociated within the intra-metropolitan space. One could reverse the narrative and, observing the division of labor, would assume a rather "integrated polycentricity" as each economic center would have a definite role in the spatial organization. This point cannot be settled until we manage to shed light on economic flows exchanged between these places as integration requires dense and regular relations in the day-to-day functioning of the economic system.

The Ile-de-France's regional average shows a diversified profile already depicted in the scientific literature [START_REF] Beckouche | Géographie économique de la région parisienne[END_REF]. From a mere large economic sectors point of view, if business services represent almost 65 percent of all peri-productive jobs, far ahead of Transports and Telecom and Finance-Bank-Insurance industries (respectively 22 and 13 percent), when examined closer at detailed economic subsectors, it appears that no activity exceeds 15 percent of regional peri-productive jobs (Figure 8). Transports, Bank-Insurance, Management and wholesale trade are the four most important with a share of 13 to 14 percent. With values only half as big, IT, telecom, and other general services to firms rank second. All other activities account for under 5 percent of Ile-de-France's peri-productive employment (R&D, marketing, engineering). In terms of broad functions, the Immaterial production activities (conception, management, marketing) are more important than "concrete" ones (63 and 22 percent of regional peri-productive jobs, respectively) (Figure 9). This indicates the strong extent to which the Parisian productive system is involved in the development of a knowledge-intensive and information economy [START_REF] Ascher | The global capacity of a city: A relational study of London[END_REF]).

Among the 21 economic centers mentioned, only a few are close to the regional average, hence confirming an intense differentiation within the metropolitan region. The near average economic centers are located in Paris City (such as southeast Paris, middle-east Paris, or east Paris) or in the Inner Suburbs (Créteil). All being respectively in the dense part of the agglomeration, they are urban centers, sometimes even with an important number of producer services jobs. Their economic sector profile is diversified, their functions are predominantly those of Abstract production and their share of high-order services jobs is not especially strong. However, these economic centers remain the exception in an economic system where specialization is the norm, as for instance in the business districts.

Economic Centers' Specialization Business Centers.

Business centers are defined as having predominant Management and Finance-Bank-Insurance activities, abstract functions largely exceeding the Where are these secondary economic centers located? In the case of the two economic centers of Saint-Denis and the north Hauts-de-Seine, they are located in some traditionally industrialized places of the Inner Suburbs presently undergoing economic conversion processes. There, logistics and wholesale trade account for over half of all producer services jobs (a quarter only in the regional average). Although a bit more diversified, the Villes Nouvelles (Saint-Quentin-en-Yvelines excluded) have yet a rather high proportion of material production functions. Only Cergy in the north appears a little closer to the regional average as it has a nonnegligible share of Management activities. Lastly, a little aside in this category, Roissy and Orly airports are, as can be expected, specialized in material production (over half of their jobs against a regional average under a quarter), which can be explained by the importance of logistics activities.

To sum up, the functional-and sector-based analysis of the 21 main economic centers demonstrates bold intra-metropolitan specialization between a metropolitan core dedicated to business activities and Management functions; a southwestern "technopolitan" area leading high-technology industries and R&D functions; and the remaining downstream activities centers in the Inner and Outer Suburbs. How then does this spatial division of the peri-productive system change the labor market geography? I will explore this question before I turn to my conclusion.

Sub-fragmentation of a Once Integrated Labor Market?

Regional and national planners as well as scientists have long been insisting on the role of a large and integrated labor force market to explain the high economic productivity of the Paris metropolitan region.2 At least as early as 1965 with the "Schéma Directeur d'Aménagement Urbain de la Région

Parisienne", regional planning documents underline the necessity of a developed and efficient infrastructure system enabling the transportation of virtually all workers anywhere in the region, thanks to urban highways or the Regional Express Railway. The coherence of a compact and interconnected labor market has even been put forward as a key explanation for the higher productivity of the Paris region over other French cities [START_REF] Rousseau | Les bénéfices de la concentration parisienne[END_REF].

The transformation of the Paris agglomeration from a monocentric city to a more polycentric metropolitan region can have strong impacts on the once praised integration of the labor force market. As it has been shown in North

American metropolitan regions such as New York [START_REF] Godfrey | Restructuring and decentralization in a world city[END_REF], European cities, traditionally described as less fragmented than other urban regions in the world, might be at a turning point with the constitution of sub-regional labor which is defined as the number of municipalities sending at least 10 producer services workers toward the economic center, and the "polarizing intensity" which refers to the number of municipalities sending at least 10 percent of their producer services workers to the economic center studied. The first indicator measures the maximal geographic range of the economic center, the second its capacity to command fully or partly a labor market. Figure 11a illustrates these two indicators: a municipality belongs to the attraction range of an economic center if its color is everything but white; conversely, it is part of the polarized area if darkened.

Paris: A Decreasing Influence.

In 1982, Paris Financial City's influence is predominant within the agglomeration (Figure 11a). Its attraction range exceeds 650 of the 1,300 municipalities allowing it to recruit workers far into the Outer Suburbs, especially along the RER A train line. Its influence is a bit stronger in the northern half of the region affecting as many as 580 municipalities in the whole region. Twenty years later, the situation has dramatically changed. If its attraction range has slightly increased (10 percent), following in doing so the expansion of the metropolitan area, Paris Financial City suffers a strong diminution of its capacity to command a regional labor market. Its polarizing intensity has diminished by half between 1982 and 1999. In other words, if Paris Financial City is still the biggest economic center, it is not as predominant as it used to be as a labor force recruitment area.

neighboring municipalities, and even a bit further in the eastern fringe of the Yvelines département.

Twenty years later, La Défense has vigorously consolidated its position within the regional labor market. Its polarizing intensity has increased by 150 percent, that is to say one of the strongest positive variation rates, a spectacular result considering its already important size in 1982. It is now ranking second by its extent with 560 municipalities, closely following Paris Financial City. In fact, almost the entire metropolitan region is now within reach of La Défense.

Moreover, with 150 municipalities polarized, it commands a large northwestern sector if not the entire western half of the region. Not being quite as influential as Paris, La Défense is helping the French capital city to maintain the integration of a fragmenting regional labor market.

Sub-fragmentation in the Outer Suburbs.

All the other influence-growing economic centers are located in the Outer Suburbs: Roissy, the five villes nouvelles, and Saclay have witnessed a powerful reinforcement of their attraction range, far exceeding the general metropolitan expansion. They consolidate their polarizing intensity thanks to variation rates over 150 percent, figures that cannot be explained only by the weakness of their situation in 1982. Their polarization area is not going toward central sites of the agglomeration but in the direction of all Outer suburbs' municipalities. Resisting against a traditionally dominant Parisian center, competing successfully with intermediate economic centers located in the Inner Suburbs, they show an evident ability to turn themselves into sub-regional labor market centers. Saint-Quentin-en-Yvelines, for instance, is going from a situation in 1982 where it used to command only a few neighboring municipalities to a broad influence in 1999 over a large southwestern part of the region. As a result, a two-faced phenomenon can be observed. At the regional scale, the strong development of La Défense, while making up for the relative stagnation of Paris, tends to uphold the existence of a metropolitan labor market. Meanwhile, at a more local level, secondary economic centers, located far enough from the metropolitan triangle core, are growing steadily and become sub-regional labor market centers.

Conclusion

The last 20 years of metropolitan economic geography have seen dramatic changes in the Paris region. To understand this complex reorganization, I insisted first on the importance of carefully choosing the scale of analysis. Zooming from business district versus inner and outer suburbs analyses to the municipal scale enabled us to shed new light on metropolitan economic system's transformations. Four main observations have been made. First, the decentralization trends of business services are affecting the Paris region even if its inherited geography seems to be resistant. Spatially, the form of the business services decentralization is not dispersed but on the contrary polycentric ("concentrated deconcentration"). This polycentricism occurs within the limits set by Paris' specific geography, that is to say one of a rather small and dense agglomeration. Second, decentralization dynamics do not mechanically induce the decline of the traditional business district. The Paris case shows that not only is economic centrality still a key-element to understand contemporary economic trends, but also that the central metropolitan service pole is enlarging its position while concentrating upper market activities. Its strength is such that it tends to Fourth, the constitution of a more polycentric urban region seems to induce a transformation of the labor market geography. If the core area manages to keep a regional influence on the entire metropolis, mainly thanks to the increasing influence of La Défense, secondary economic centers located in the Outer Suburbs are able to organize partly or fully sub-regional labor markets. In other word, both integration and fragmentation trends coexist.

It must be stated that this paper did not intend to explain the factors causing the reorganization of Paris metropolitan economic geography but rather to detail as precisely as possible the spatial dynamics affecting the productive system. It is therefore the first step of a research agenda that proposes two avenues for further analyses. The first one is to study some factors that have been depicted in the literature as key-elements to understand what seems to be a new metropolitan economic geography. A brief introductory list would include the analysis of corporate organizational and spatial strategies as the change in market scale induces a reconfiguration of the internal organization of firms in a globalization context [START_REF] Mucchielli | Multinationales et mondialisation[END_REF]; the study of the real estate market as there seems to be a shift from a demand-driven market to a more supplyoriented economy where investors and real estate developers arbitrate risk and profit according to the location within the metropolitan region -central location often minimizes risks when peripheral locations maximize profit (Nappi-Choulet 1997); and the observation of public institutions in terms of planning principles, which have been important in the case of Paris in terms of modeling perceptions of other key-actors, and of actions (investments, territorial marketing, etc.) in order to promote a more polycentric pattern. The latter question is all the more central today as a new regional Schema Directeur is in preparation.

The second axis of this research agenda points in another direction which aims not only at explaining spatial dynamics but also at describing the day-to- region (1982-1999). Sources: Insee/Iaurif, National Census 1982 -1999. France region (1982France region ( -1999)). Sources: Insee/Iaurif, National Census, 1982, 1999

1

  The polycentric city-region that never was: Paris agglomeration, Bassin parisien and spatial planning strategies in France Ludovic Halbert Researcher, Université Paris-Est, LATTS, (UMR CNRS 8134) ENCP-LATTS, 5 Rue Einstein, 77455 Champs-sur-Marne Tel : 01.64.15.38.39 Mail : ludovic.halbert@enpc.fr Website: http://latts.cnrs.fr/site/p_lattsperso.php?Id=1092 Please quote the published version: HALBERT L., 2004, "The intrametropolitan Decentralization of Business Services in the Paris Region: Patterns, Interpretation, Consequences", Economic Geography, 80(4), 381-405

  /Issy-les-Moulineaux/Paris' southern districts, located mostly in the eastern part of the Hauts-de-Seine département (120,000 peri-productive jobs). The rest of Paris' western districts and of the municipalities linking the French capital city to La Défense (Neuily-sur-Seine, Levallois-Perret and Clichy) must be added to depict what is the new golden triangle of the Paris region. Altogether, it is nothing less than 610,000 peri-productive jobs, almost 40 percent of the regional total.

  force. Business services gather over half of the total, well ahead of the Manufacturing (20 percent), Banking (12 percent) and Transport & Telecom (11 percent) sectors. In terms of functions, Management is predominant (53 percent), followed by Marketing (17 percent) and Research-Development (16 percent).

  regional average, especially in Marketing and Management, and an important proportion of high-order services. Five business centers meet these criteria in the Paris region, four of which constitute the central metropolitan triangle: Paris-Financial City, Paris' western districts, La Défense, Boulogne-Billancourt/Issy-les-Moulineaux, and, in the Outer Suburbs, Saint-Quentin-en-Yvelines.

  markets. In order to evaluate the reality of such a phenomenon and to measure to what extent it can be explained by the deconcentration hypothesis, I propose to map commuting producer services jobs of the 21 economic centers identified earlier. Two simple cartographic indicators are being used: the "attraction range"

  spread to neighboring spaces (La Défense, Boulogne-Billancourt/Issy-les-Moulineaux). Third, the constitution of a more polycentric metropolitan region is correlated to a strong spatial differentiation of services activities (what I have called in the paper "dissociated polycentricity"). If main business services are still located in a widened metropolitan core, high-technology and R&D activities are gathered in the southwestern part of the region and most downstream activities are concentrated in secondary economic centers in inner and outer suburbs.

  day functioning of the urban system. Against what is a static geography informing only characteristics of spaces, a new geography must be undertaken in order to improve our understanding of the spatial working of the productive system in its day-to-day relationships. In Castells's terminology, it is necessary to go beyond a geography of places to one of flows. Does a polycentric shape induce systemic relationships? In other words, do economic centers constituting the polycentric geography of the metropolis actually exchange flows of data, money, information, and workforce? This poses a challenge as public statistics are not adequate to work at the metropolitan scale nor at the firms level. To do so, it is necessary to invent new data sources. Qualitative work based on firms interviews or on theoretical firms networks are one way to achieve such a difficult goal (see GaWC analyses on the global networks). The other is to create comprehensive databases that record firms' flows as I am currently doing with the French national public operator in the case of the Paris metropolitan region.

Figure 1 .

 1 Figure Captions:

Figure 2 .Figure 3 .Figure 4 .

 234 Figure 2. Départemental distribution of Paris region peri-productive employment (1999). Sources: Insee/Iaurif, National Census, 1999 Figure 3. Départemental peri-productive employment variation rate (1982-1999). Sources: Insee/Iaurif, National Census, 1982 -1999 Figure 4. Peri-productive employment in Ile-de-France region map (1999).Sources: Insee/Iaurif, National Census 1999.

Figure 5 .

 5 Figure 5. Map of high-order services employment in Ile-de-France region (1999). Sources: Insee/Iaurif, National Census 1999.

Figure 6 .

 6 Figure 6. Map of high-order services employment variation in Ile-de-France

Figure 7 .

 7 Figure 7. Départemental variation of high-order services employment in Ile-de-

Figure 8 .

 8 Figure 8. Ile-de-France region branch activities profile. Sources: Insee/Iaurif, National Census, 1999.

Figure 9 .

 9 Figure 9. Ile-de-France region functions profile. Sources: Insee/Iaurif, National Census 1999.

  Figures:Figure1:

  Figure 3:

  Figure 4:

  Figure 5:

  Figure 7:

Figure 11b:

  Figure 11b:

Coefficient of concentration or Herfindahl coefficient = square sum of municipal shares. The stronger the coefficient, the higher the concentration. If a coefficient is high, then only a few municipalities gather a large part of employment.

The term "integrated" is understood as reflecting the fact that most municipalities of the metropolitan region were sending an important share of their commuters to the economic core of Paris.

Slight differences distinguish these economic centers. The Financial City and Western districts of Paris are the traditional financial and headquarters centers. For instance, in Paris' Financial City, the banking and insurance industry counts for no less than 35 percent of peri-productive employment while Management activities represent 18 percent (Figure 10). La Défense, while also a financial center, is home to Wholesale trade and IT companies as well in quite a large proportion. Boulogne's economic center is more specialized in the telecom and media industries. As for Saint-Quentin-en-Yvelines, its profile is in-between two categories. It is impossible to deny its business-oriented profile as Management activities are important (14 percent). However, this ville nouvelle also has an economic profile close to neighboring suburban economic centers that show a more high-technology and research-development-oriented profile.

Southwestern "Technopolitan" Centers.

"Technopolitan" economic centers [START_REF] Benko | Géographie des technopôles[END_REF] are specialized in hightechnology activities such as IT, telecom, R&D or engineering, in a way far exceeding the average of the Ile-de-France region. This reflects an upstream activities orientation. In terms of functions, it is no surprise that immaterial production dominates, with research and conception jobs being overrepresented. This explains why these economic centers have the highest rate of high-order services in the region, outnumbering even the central core.

Straddling the Yvelines and the Essonne departments, the "technopolitan" centers are gathered in a clearly-delimited southwestern part of the Outer Suburbs. On top of Saint-Quentin-en-Yvelines, the Hauts-de-Seine Sud, Vélizy-Villacoublay, Saclay, and Massy belong to this high-technology employment category. If each center has its own specificities -such as Saclay, for instance, which is dedicated to research activities -overall, they express the same "technopolitan" specialization.

Downstream Activities Economic Centers.

The remaining economic centers all fit the same profile. In terms of economic sector, downstream activities such as logistics or wholesale trade are over-represented. Incidentally the material production functions, if not always prevalent, are more important than in the regional average. Moreover, employment in high-order services is low. What about the other economic centers within Paris? All of them seem to be suffering the same decline. For instance center and east Paris (10th, 11th, and 19th arrondissements) used to be in 1982 the second economic site both in terms of attraction range and polarizing intensity in the Ile-de-France region (with respectively 450 and 150 municipalities). Its polarization area was sensed as far as the Outer Suburbs' fringes of a large eastern half of the agglomeration.

In 1999, its polarizing intensity has crumbled with a 75 percent decrease in the polarization area. Today, it commands solely its own districts and a few small and far away municipalities.

Inner Suburbs: Too Strong a Competition.

The Inner Suburbs' economic centers located close to Paris face the same difficulties. No matter how fast growing they are, their influence within the metropolitan region has not strengthened. Créteil for instance with an attraction range of 100 municipalities in 1982 and 173 in 1999 has not managed to reinforce its capacity to command a local labor market: in 1982 it polarized no municipalities but itself, in 1999, it is still limited to 10 small residential municipalities of its immediate surroundings. This observation on stagnating economic centers is also verified with a fast growing center such as Boulogne-Billancourt/Issy-les-Moulineaux. Even though it has become a major central economic concentration within the metropolitan business core, it has seen its polarizing intensity decline by over a third between 1982 and 1999. This observation can be extended to Vélizy-Villacoublay (Figure 11b), an important economic center specialized mostly in high tech industries. In conclusion, all Inner Suburbs' economic centers, squeezed between Paris and the Outer Suburbs act as if stopped in their capacity to command a well delimited labor market area. All but one.

The Spectacular Growth of La Défense.

In 1982, La Défense had already acquired a reasonable weight considering its short history, the first office tower being built in 1964. With an attraction range only a little under 400 municipalities and a polarizing intensity close to 50 municipalities, it used to be part of the secondary economic centers by size following those of Paris. It managed to command the labor market of its


A Kermarrec

H Mauleon

C Sirjusingh

L Baud

Etude expérimentale de la sensibilité de vertébrés hétérothermes tropicaux (crapaud, grenouilles, lézards) à diverses souches de nématodes entomoparasites des genres Heterorhabditis

et Steinernema.

SUMMARY

Agressivity of Heterorhabditid and Steinernematid entornopathogenic nematodes against the earliest tadpole instar of the toad Bufo marinus varies with the strain used. Adults of the iguanid lizard Anolis marmoratus may also be adversely affected by some strains of entomopathogenic nematodes. Adults of the frog Eleutherodactylus sp. are not affected. Massive dermic inoculations of Xenorhabdus spp to white mice (Mus muscuIus) did not induce any dermatitis.

INTRODUCTION

Howorth (1991), souligne les impacts environnementaux négatifs de certains contrôles biologiques classiques et insiste sur les risques encourus par des espèces sauvages non cibles, et plus particulièrement clles en danger d'extinction. L'auteur ne fait cependant pas référence aux quelques publications récentes (Kermarrec & Mauléon, 1985 ;[START_REF] Poinar | Infection of frog tadpol" (Amphibia) by Insect, parasitic nematodes (Rhabditina)[END_REF][START_REF] Poinar | Non-insect host for the entomopathogenous rhabditoid nematodes Neoaplectana (Steinernematidae) and Heterorhabditis (Heterorhabditidae)[END_REF] signalant que des vertébrés hétérothennes de la faune sauvage présentent une nette sensibilité à certains nématodes entomopathogènes Heterorhabditidae et Steinernematidae.

Les risques environnementaux de l'utilisation brutale d'agents biologiques sous les tropiques ne sont pas nuls et peuvent théoriquement être plus importants qu'en climat tempéré. Ces effets indésirables sont accrus par la richesse et la complexité relatives des écosystèmes tropicaux et aussi parce que la plupart des recherches écologiques ont été effectuées en climats tempérés avec de nombreuses conclusions totalement inadaptées aux régions chaudes. Trop peu est, de ce fait, connu quant à la biodiversité, l'écologie, la structure des communautés, les interrelations trophiques qui président au fonctionnement normal des biocénoses tropicales, même pour les zones cultivées les plus entropisées. De plus, il entre clairement dans la mission et les devoirs du chercheur en lutte biologique de se préoccuper des éventuels effets secondaires, ou biais pervers, de ses expérimentations sur la faune ou la flore non-cible de la biocénose concernée.

Quelques publications concernent les interactions entre les nématodes entomopathogènes et les vertébrés. Les auteurs concluent tous à l'innocuité totale pour les homéothermes (Gaugler & Malory Boush, 1979;[START_REF] Jackson | Cuticular fine structure and molting of Neoaplectana glaseri (Nematoda), after prolonged contact with rat peritoneal exudate[END_REF]Kermarrec & Mauléon, 1985;[START_REF] Kobayashi | Recent advances in Biological control of pests by entomogenous nematodes in Japan[END_REF][START_REF] Poinar | Nematodeas facultative parasites of insects[END_REF][START_REF] Poinar | Non-insect host for the entomopathogenous rhabditoid nematodes Neoaplectana (Steinernematidae) and Heterorhabditis (Heterorhabditidae)[END_REF][START_REF] Poinar | Inoculation of entomogenous, nematodes , Neoapleetona and Heterorhahditis;, and their associated,. bacteria, Xenorhabdus spp., into chicks and mice[END_REF]Schmiege, 1962[START_REF] Schmiege | The feasibility of using a ncoaplectanid nematode for contro1 of some forest insect pests[END_REF]Wangetal., 1983).

Le présent travail apporte plus de précisions aux résultats qui furent acquis antérieurement par Kermarrec & Mauléon (1985) à l'aide d'une seule souche ("Agriotos") de Neoaplectana (Steinernema) carpocapsae contre un seul vertébré: le crapaud Bufo marinus. L'éventail des tests de sensibilité a pu être ouvert à dix souches appartenant aux deux principaux genres de nématodes Rhabditides entomoparasites (Heterorhabditis et Steinernema). Les cibles sont également multipliées et constituées par trois vertébrés hétérothermes de la faune naturelle des Antilles: le crapaud Bufo marinus, la petite grenouille siffleuse Eleutherodactylus sp. et le lézard iguanide vert Anolis marmoratus. [START_REF] Poinar | Infection of frog tadpol" (Amphibia) by Insect, parasitic nematodes (Rhabditina)[END_REF] Ces nématodes sont multipliés sur des chenilles de Galleria melionella (Lépidoptère, teigne des ruches) élevées sur milieu semi-artificiel à base de cire et de pollen sans addition de substance antibiotique.

-Les bactéries symbiotiques

Les bactéries du genre Xenorhabdus qui accompagnent les nématodes entomopathogènes sont isolées à partir des souches précédentes et cultivées axéniquement sur milieu artificiel en veillant à les maintenir dans leur phase 1 (Boyer-Giglio & [START_REF] Boyer-Giglio M. R | La variation de phase chez les Xenorhabdus spp[END_REF]. Les souches testées par scarification sur souris sont présentées au Tableau 2 Tableau 2: Liste des espèces et souches de Xenorhabdus utilisées en scarification dermique ventrale de la souris blanche.

Nématode vecteur

Espèce bactérienne Réf. bibliographique

Steinernema carpocapsae (breton)

Heterorhabditis bacteriophora . (HG01)

Xenorhabdus nematophilus Photorhabdus luminescens

Boemare & Brehelin, 1990 [START_REF] Boemare | Taxonomie et propriétés générales des Xenorhabdus, bactéries associées aux nématodes entomophages Steinernematidae et Heterorhabditidae[END_REF] 3 -Les vertébrés cibles Homéothermes : la souris blanche (Mus musculus), élevée en animalerie du laboratoire ClRAD-IEMVT, a subi le test de scarification dermique avec les bactéries symbiotiques.

Hétérothermes : les batraciens retenus sont (1) le crapaud Bufo marinus aux stades tétards pêchés à l'aide d'un filet à plancton en eaux libres (formes apode: stade I ; avec pattes Enfin, un lézard Iguanidae, Anolis marmoratus, est capturé dans la nature au stade adulte par la méthode du lasso. Ces petits lézards américains sont sensibles au stress et de nombreux décès sont observés dans les témoins si l'on ne prend pas quelques précautions élémentaires: périodes de repos, alimentation ad libitum et élimination des individus les moins bien portants avant l'expérimentation.

-Inoculations

Les souris sont scarifiées sur la paroi ventrale préalablement épilée et désinfectée. Une crème de Xenorhabdus spp (Tableau 2) est étalée sur la plaie. Les réactions dermiques postérieures sont notées tous les jours (éventuelles rougeurs, inflammations, septicémies, et cicatrisations) .

Les adultes d'A. marmoratus et d'Eleutherodactylus sp. recoivent chacun, per os à la seringue et en une prise, 80 000 stades infestants des différents nématodes (Tableau 1). L'adulte de B. marinus reçoit en une prise 80 000 nématodes per os. Ses tétards sont mis en contact avec des concentrations de 20 à 100 nématodes par cm2 de fond de cuve expérimentale en verre remplie d'eau. Les animaux testés sont alimentés, autant que faire se peut, après l'infestation.

Les répétitions ne sont jamais inférieures à 30 individus par test et les effets sont notés journellement, jusqu'à 30 jours si nécessaire. Les cadavres sont disséqués (ou digérés à la pepsine selon la méthode de Mauléon et al., 1991) et les nématodes dénombrés à la loupe binoculaire par stade de développement selon les organes atteints. Certaines expérimentations douteuses ou sensibles (mortalité forte des hôtes, développement des nématodes en adultes reproductifs,...) sont automatiquement répétées pour confirmation. Toutes les mortalités sont pondérées parcelle des témoins selon Abbott (1925). ,,-' Les foies les pfus manifestement septicémiés des A. marmoratus sont prélevés aux fins d'isolements et de détenninations bactériologiques.

RESULTATS

-Résultats négatifs

Aucune septicémie, ni inflammation même minime, n'est apparue sur le ventre des souris scarifiées et inoculées massivement par les bactéries symbiotiques. La cicatrisation des plaies de scarification a été constamment rapide, totale et homogène. Aucune mortalité n'est apparue chez les adultes des batraciens, crapaud ou grenouille, inoculés per os avec de fortes doses de nématodes entomopathogènes.

-Résultats positifs

Les tétards de B. marinus sont sensibles aux larves infestantes des nématodes parasites d'insectes. Cette sensibilité, marquée par une mortalité élevée, varie avec les souches et l'age du tétard cible (Figures 1 et 2). La résistance du tétard au stade 2 (avec pattes arrières) n'est réelle que pour les souches DD136 et AIl de Steinernema carpocapsae (Figures 2 et 3). La réduction de cinq fois des concentrations en nématodes infestants dans les cuves expérimentales laisse encore apparaître des mortalités Abbott considérables (Figure 4 ). Les Steinernema se retrouvent en général vivants (mais non évolués) dans la cavité générale des tétards alors que les Heterorhabditis se cantonnent dans l'intestin de l'hôte. Seulement pour la souche "breton" de S. carpocapsae, prés de 5% des nématodes infestants se sont développés en adultes féconds (présence de L3 de première génération) dans la cavité générale du stade 2 des tétards de B . marinus. Les anolis adultes sont parasités naturellement par des Oxyurides Pharyngodonidae et surtout des Trichostrongyloides sp. Quatre souches de nématodes entomoparasites ont entrainé des monalités Abbott remarquables aprés l'inoculation per os de 80 000 larves infestantes (Figure 5). Seule la souche "breton" de S. carpocapsae a permis d'observer des larves L3 (i.e. infestantes et non développées) vivantes dans la cavité générale des lézards morts. Le genre : Heterorhabditis laisse apparaître des nécroses intestinales à caractère hémorragiques et des invasions bactériennes au niveau du foie, mais aucune survie des L3 infestantes. Les analyses 1 ::. bactériologiques ont révélé la présence de Pseudomonas aeruginosa dans les foies après . infestation par les souches K53, K87 et HG02 de St François. Le genre Vibrio est apparu chez les anolis infestés par H.

DISCUSSION ET CONCLUSIONS

L'engouement actuel de nombre de chercheurs dans le monde entier pour les nématodes parasites d'insectes, avec pour objectif un contrôle biologique des arthropodes nuisibles, est : tout à fait remarquable. Cette observation souligne l'intérêt porté à ces agents biologiques "à , têtes chercheuses", intérêt reposant sur une base objective de belles réussites expérimentales passées et présentes. C'est, de plus, le biopesticide qui a intéressé le plus d'industriels, avec un développement réel, soutenu et accessible au grand public d'une petite dizaine de spécialités et marques commerciales (USA, UK, Hollande, Italie, Australie... en ajoutant quelques pays socialistes, grands producteurs: Cuba, URSS, Chine...). Le nombre de sessions spécialisées, de séminaires internationaux, de rencontres portant spécifiquement sur les nématodes entomoparasites est un autre signe de la vitalité de ce thème de recherche. Des projets internationaux de recherche sur ces helminthes existent: Chine-Autralie, Allemagne-Tonga, France-Cuba, USA-Caraïbes,... et, en projet, CEE-Caraïbes avec la base INRA en Guadeloupe.

Très tôt (Schmiege, 1962), des chercheurs se sont interrogés sur l'innocuité de ces vers pour la faune vertébrée, de l'Homme aux hétérothermes. La conclusion actuelle, fondée sur de très nombreuses expériences publiées ou non, est que la faune homéotherme (dont l'Homme) est totalement insensible à ces nématodes. Cette opinion prévalait pour les vertébrés poïkilothermes jusqu'à la démonstration dès 1974 (publiée par Kermarrec & Mauléon, 1985) dans nos laboratoires de la haute sensibilité des stades les plus jeunes du crapaud buffle Bufo marinus à Steinernema carpocapsae (souche agriotos). Cette observation fut rapidement confirmée par [START_REF] Poinar | Infection of frog tadpol" (Amphibia) by Insect, parasitic nematodes (Rhabditina)[END_REF] sur les plus jeunes tétards de la grenouille Hyla regida. Il est du devoir du chercheur d'aller jusqu'au bout de ses observations, mais également de les ramener à leur juste signification en prenant en compte la complexité biologique des systèmes hétérogènes qui forment le champ de ses expérimentations (agrocénoses, zones naturelles...). Cette double démarche a été la nôtre dans ce travail.

(A) : aller jusqu'au bout des observations objectives: nous avons montré que la sensibilité des batraciens et des sauriens dépend essentiellement (1) de la souche de nématode entomopararasite utilisée, et (2) du stade de développement de la cible vertébrée. Plus la cible est jeune (membranes ectodermiques fines et fragiles, [START_REF] Poinar | Infection of frog tadpol" (Amphibia) by Insect, parasitic nematodes (Rhabditina)[END_REF], plus la nocuité est grande. Le parasite meurt en général avec l'hôte. Cependant, dans quelques cas de faible fréquence (5%, pour la souche "breton" de S. carpocapsae sur les tétards de B . marinus), le parasite effectue son développement complet dans l'hôte tant que l'état du cadavre le lui permet. Rappelons, avec [START_REF] Poinar | Non-insect host for the entomopathogenous rhabditoid nematodes Neoaplectana (Steinernematidae) and Heterorhabditis (Heterorhabditidae)[END_REF], que l'exosquelette des hôtes arthropodes procure un avantage écologique certain au parasite. Il lui offre, en effet, un espace clos et protégé (donc homeostaté) pour quelques cycles de reproduction jusqu'à l'épuisement des réserves alimentaires constituées par les organes internes lysés par la population bactérienne que le nématode y a installée. Le facteur limitant, dans un arthropode, est la biomasse transformable au profit des générations de vers.

(B) : pondérer la signification réelle des résultats expérimentaux, obtenus in vitro, avec une bonne connaissance des contraintes de la réalité écologique des agrosystèmes. Certes, les tétards de crapaud meurent rapidement face à de faibles doses de certaines souches de nématodes entomoparasites, et il en va de même d'anolis adultes! Il peut paraître inquiétant qu'un vertébré soit tué par ces nématodes. Il faut, toutefois, s'affranchir de l'irrationnel et observer les conditions de nos expérimentations, puis la réalité du terrain.

L'expérimentation a été menée in vitro en optimisant volontairement tous les paramètres de survie de l'inoculum, de maintien de sa virulence et de contact avec l'hôte. Les stades infestants du parasite sont introduits, frais et actifs, dans un milieu oxygéné, sans DBO, sans prédateurs, sans contrainte physico-chimique liée au substrat sur lequel ils sédimentent rapidement et où les tétards, dans leur comportement de prise de nourriture, ne peuvent que Ces faits ont une probabilité excessivement rare de se réaliser sur le terrain. De plus, comme indiqué ci-avant, chez les vertébrés de nos expérimentation, le facteur limitant le développement des populations de vers est, d'évidence, la destruction rapide de l'intégrité du corps (limites molles avec l'extérieur) de l'hôte. Les facteurs écologiques externes agissent dès lors immédiatement et défavorablement sur le potentiel de développement ultérieur des populations du parasite, même si une importante biomasse reste encore disponible pour assurer plusieurs cycles de reproduction de celui-ci.

Le contact avec les tétards de crapaud ne pourrait se faire qu'en cas de traitement de points d'eau avec des nématodes parasites d'insectes dans le cadre d'une lutte anti-moustiques. D'une part, cette lutte est loin d'être au point, et, d'autre part, même à forte doses, la sédimentation rapide des larves infestantes des nématodes vers le fond anoxique (et souvent mou sur plusieurs centimètres) des points d'eau nous paraît annuler rapidement toute chance de contact avec les tétards.

Enfin, les populations de tétards sont denses et l'espèce est loin d'être en voie de disparition.

Dans le cas particulier des iguanides, le contact avec les nématodes entomoparasites n'est possible que par l'intermédiaire d'insectes morts et emplis de parasites. Les anolis sont des chasseurs de proies mobiles, pas des nécrophages: ceci élimine, à notre sens, pratiquement le risque.

En ce qui concerne les bactéries symbiotiques, elles ne sont certainement pas pathogènes pour la souris au niveau dermique. Ce ne sont pas non plus les bactéries symbiotiques des nématodes que l'on retrouve dans le foie des anolis morts, mais des bactéries opportunistes apparues à la faveur d'une chute du système immunitaire sous le choc de l'inoculation forcée et de l'envahissement part les nématodes.

Il n'y a, en conclusion et pour l 'heure, aucune crainte environnementale majeure à avoir dans l'utilisation des nématodes entomopathogènes. Les chercheurs restent parfaitement conscients de la portée de leurs actes scientifiques. Les nématodes parasites d'insectes continuent de mériter toute notre attention pour leurs grandes qualités et potentialités dans le cadre d'une biologisation des technologies de nos agroécosystèmes.

REMERCIEMENTS

BIBLIOGRAPHIE

Figure 1 .

 1 Figure 1. Mortalités au 3ème jour des tétards de premier stade (apodes) de Bufo marinus, à la dose de 100 larves infestantes/cm2 de fond de cuve.: souche St François.

Figure 2 .Figure 3 .Figure 4 .Figure 5 .

 2345 Figure 2.Mortalités au 3ème jour des tétards de second stade (avec pattes arrières) de Bufo marinus, à la dose de 108 larves infestantes/cm2 de fond de cuve

  Comment citer ce document : Kermarrec, A., Mauléon, H., Sirjusingh, C., Baud, L. (1991). Étude expérimentale de la sensibilité de vertébrés hétérothermes tropicaux (crapaud, grenouilles, lézards) à diverses souches de nématodes entomoparasites des genres Heterorhabditis et Steinernema. In: Rencontres Caraïbes en lutte biologique/Caribbean meetings on biological control (p. 193-204). Colloques de bacteriophora d'Argentine et le genre Chromobacterium est isolé après infestation par la souche DD 136 de S. carpocapsae.

L

  'équipe technique INRA était costutuée par S. Briand, A. Jean-Bart et R. Paul; les souris proviennent de l'élevage du CIRAD-IEMVT et les contrôles pathologiques ont été assurés par le Dr N. Barré (Mission IEMVT de Guadeloupe). Certaines souches de nématodes proviennent de la collection du Laboratoire des Nématodes entomoparasites de l'INRA à Antibes (C. Laumond). Le Pharyngodonidae (Oxyuride) a été déterminé par le Professeur Chabaud du Muséum National d'Histoire Naturelle de Paris.

Tableau 1. Liste et code des souches de nématodes entomoparasites utilisés dans les tests de sensibilité des vertébrés hétérothermes antillais. (*): deux écotypes de Heterorhabditis sp. ont été retenus dans certains tests: VH de Vieux-Habitants (Sud Basse-Terre, Guadeloupe) et SF de Saint-François (Est Grande-Terre, Guadeloupe).

  avaient complété et confinné nos résultats de 1985 en soumettant deux grenouilles (Hyla regida, Hylidae,et Xenopus laevis, Pipidae) à deux nématodes: S. carpocapsae , souche All et Heterorhabditis heliothidis, souche NC.

		MATERIELS ET METHODES
	l -Les souches de nématodes entomopathogènes
	La nature et l'origine des nématodes retenus pour ces expérimentations sont présentés dans le Tableau 1.
	Genre et espèce	Hôte d'origine	Provenance	Code souche
	Heterorhabditis bacteriophora heliothidis bacteriophora	Sol Pachnaeus litus Sol	Argentine Cuba St François Guadeloupe	Hb Arg P2M HG02
		Diaprepes abbreviatus	Vieux Habitants	HG01
	Steinernema anomali bibionis carpocapsae	Anomalia dubia Sol Laspeyresia pomonella Vitacea polistiformis	URSS France (Champagne) USA ( Virginie) USA (Georgie)	K87 K53 DD136 All
		Otiorhynchus sulcatus	France (Bretagne)	Breton
		Sol	USA (Floride)	SgFl
	glaseri	Sol	USA (Floride)	SgK72

Comment citer ce document :

Kermarrec, A., Mauléon, H., Sirjusingh, C., Baud, L. (1991)

. Étude expérimentale de la sensibilité de vertébrés hétérothermes tropicaux (crapaud, grenouilles, lézards) à diverses souches de nématodes entomoparasites des genres Heterorhabditis et Steinernema. In: Rencontres Caraïbes en lutte biologique/Caribbean meetings on biological control

(p. 193-204)

. Colloques de

  Eleutherodactylus sp. dont le développement larvaire, affranchi de l'eau libre, s'effectue entièrement dans un mucilage déposé lors de la ponte sous les litières de feuilles ou sous des pierres. Les captures s'effectuent à la main.

Comment citer ce document : Kermarrec, A., Mauléon, H., Sirjusingh, C., Baud, L. (1991). Étude expérimentale de la sensibilité de vertébrés hétérothermes tropicaux (crapaud, grenouilles, lézards) à diverses souches de nématodes entomoparasites des genres Heterorhabditis et Steinernema. In: Rencontres Caraïbes en lutte biologique/Caribbean meetings on biological control (p. 193-204). Colloques de arrières: stade II) et (2) les adultes des petites grenouilles siffleuses

  et les avaler. Quant aux lézards anolis, la prise de 80 000 vers en une fois doit correspondre, ramené à l'échelle humaine, à une soupière pleine à avaler d'un trait.

Comment citer ce document : Kermarrec, A., Mauléon, H., Sirjusingh, C., Baud, L. (1991). Étude expérimentale de la sensibilité de vertébrés hétérothermes tropicaux (crapaud, grenouilles, lézards) à diverses souches de nématodes entomoparasites des genres Heterorhabditis et Steinernema. In: Rencontres Caraïbes en lutte biologique/Caribbean meetings on biological control (p. 193-204). Colloques de les rencontrer