Bilan des recherches menées par le groupe inter-organismes ACTA-INRA-SPV* sur la biologie d'Arvicola terrestris scherman en France (1979–1987)1

A l'issue de deux phases de forte densité des populations d'Arvicola terrestris scherman en France, un groupe de travail inter-organismes ACTA-INRA-SPV a été constitué pour entreprendre un programme de recherche sur ce rongeur, dans le but d'en contrôler les populations. C'est à l'INRA que revient le rôle de coordonner les travaux et notamment d'assurer les études sur la biologie de l'espéce. L'ACTA a mené des études en captivité, ainsi qu'une expérimentation de plein champ en Haute-Savoie. Enfin, le SPV a pris la responsabilité de l'évaluation au champ des rodenticides et du développement d'un systéme de prévision en Franche-Comté et en Auvergne-Limousin. L'article résume les 8 années de travaux et souligne les questions restées en suspens. II cherche à situer le problème d'A. terrestris dans la problématique plus vaste de l'étude des rongeurs ravageurs de cultures en France et débouche sur l'analyse des choix des thématiques scientifiques qu'il convient de développer dans le contexte agricole moderne.     

Agronomic effects from the control of Agropyron repens in barley by pre-harvest application of glyphosate

Pre-harvest application of glyphosate in barley at 1·44 and 0·72 kg ha^?1 was compared with post-harvest application at 1·44 kg ha^?1 at six sites in south-east Scotland, three sprayed in 1980 and three in 1981. Both levels of pre-harvest application gave consistent 95–99% control of A. repens compared with 0–76% control from post-harvest application. Yields of crops grown in 1981 were significantly increased after all the 1980 pre-harvest treatments and after one post-harvest treatment. No significant depressions in grain germination were recorded from the lower rate of pre-harvest application but one significant depression was recorded from the higher rate. Combine harvesting throughput at a given grain loss level was significantly improved by pre-harvest application and moisture content of grain at harvest was significantly reduced by up to 2·5%. Wheeling losses from pre-harvest spraying ranged from 1 to 5%. Crop yield increases in the year after spraying compensated for herbicide and application costs plus any yield losses through tractor wheelings.     

Sensitisation to the House Dust Mite, Dermatophagoides farinae, in Dogs with Sarcoptic Mange

Abstract— Sensitisation to the house dust mite, Dermatophagoides farinae , was demonstrated by skin testing and allergen-specific IgG determination in 15 out of 20 dogs in which a definitive diagnosis of sarcoptic mange was made following recovery of Sarcoptes scabiei mites on skin scrapings. After therapy, no dogs exhibited clinical signs of atopic dermatitis. Intradermal skin testing and 40 per cent of specific IgG assays for Dermatophagoides farinae were negative 90–180 DAys after the original diagnosis.
Résumé— Une sensibilisation a l'acarien de la poussière de maison, Dermatophagoides farinae , est demontrée par tests cutanés et dosage d'immunoglobulines IgG specifiques d'allergenes sur 15/20 chiens atteints de gale sarcoptique prouvée par la presence de nombreux sarcoptes aux raclages cutanés. Après traitement, aucun chien n'a présenté des signes cliniques de dermatite atopique. Les tests cutanés intradermiques et 40 plus des posages IgG pour Dermatophagoides farinae sont negatifs 90 à 180 jours après le diagnostic initial. [Prélaud, P., Guaguère, E. Sensitisation to the house dust mite, Dermatophagoides farinae , in dogs with sarcoptic mange (Une sensitisation à l'acarien de la poussière de maison sur les chiens atteints de gale sarcoptique).     

One-dimensional biophysical modelling of fish egg vertical distributions in shelf seas

Modelling the vertical distribution of fish eggs is important when assessing fish stocks with egg production methods and for monitoring the reproductive potential of fish populations. Fish eggs are passive particles and their vertical distribution is determined by a few parameters such as egg density, egg diameter, wind‐ and tide‐induced turbulence, and vertical hydrographic structure. A one‐dimensional vertical biophysical, numerical model was developed which was adapted to the hydrography of shelf seas under the influence of tidal currents, wind‐induced circulation, and river discharges. The biological part of the model parameterized the ascent velocity of the egg as a function of egg properties (diameter, density) and water properties (density, viscosity, turbulence). The model contains a turbulence closure which makes the model dynamic. The model parameters were surface wind, tidal currents, T‐S profile, and egg diameter and density, which were kept constant in time. The model has the capacity to generate sub‐surface egg maxima in different hydrographic conditions, e.g. in areas under the influence of river plumes, and can also homogenize the egg distribution under wind and tide forcing. Sensitivity tests were carried out to study the response of the model to variations in the model parameters for a variety of hydrographic conditions. The modelled egg vertical distributions were validated by comparison of the model results with egg distributions sampled in the field. The analysis highlighted variability in fish egg density of anchovy, sardine, and sprat across years and areas, with a potential link between egg density and surface sea water density. The validated model is a tool for the analysis of shelf seas fish egg vertical distributions.     

Modelling potential spawning habitat of sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) in the Bay of Biscay

Large amplitude variations in recruitment of small pelagic fish result from interactions between a fluctuating environment and population dynamics processes such as spawning. The spatial extent and location of spawning, which is critical to the fate of eggs and larvae, can vary strongly from year to year, as a result of changing population structure and environmental conditions. Spawning habitat can be divided into ‘potential spawning habitat’, defined as habitat where the hydrographic conditions are suitable for spawning, ‘realized spawning habitat’, defined as habitat where spawning actually occurs, and ‘successful spawning habitat’, defined as habitat from where successful recruitment has resulted. Using biological data collected during the period 2000–2004, as well as hydrographic data, we investigate the role of environmental parameters in controlling the potential spawning habitat of anchovy and sardine in the Bay of Biscay. Anchovy potential spawning habitat appears to be primarily related to bottom temperature followed by surface temperature and mixed‐layer depth, whilst surface and bottom salinity appear to play a lesser role. The possible influence of hydrographic factors on the spawning habitat of sardine seems less clear than for anchovy. Modelled relationships between anchovy and sardine spawning are used to predict potential spawning habitat from hydrodynamical simulations. The results show that the seasonal patterns in spawning are well reproduced by the model, indicating that hydrographic changes may explain a large fraction of spawning spatial dynamics. Such models may prove useful in the context of forecasting potential impacts of future environmental changes on sardine and anchovy reproductive strategy in the north‐east Atlantic.     

The influence of environment and spawning distribution on the survival of anchovy (Engraulis encrasicolus) larvae in the Bay of Biscay (NE Atlantic) investigated by biophysical simulations

A growth and survival model of the early life stages was run along virtual drift trajectories tracked in a hydrodynamic model to simulate the annual recruitment process of anchovy (Engraulis encrasicolus) in the Bay of Biscay (NE Atlantic). These biophysical simulations concerning three different years were analysed in order to investigate the influence of environment and spawning dynamics on the survival of larvae and juveniles. The location of space–time survival windows suggested major environmental mechanisms involved in simulated recruitment variability at the different scales – retention of larvae and juveniles in favourable habitats over the shelf margins and turbulence effects. These small‐scale and meso‐scale mechanisms were related to the variations in wind direction and intensity during spring and summer. Survival was also variable according to the origin of the drift trajectories, that is spawning distribution in space and time. The observed spawning distribution (according to field surveys) was compared with the spawning distribution that would maximize survival (according to the biophysical model) on a seasonal scale, which revealed factors not considered in the biophysical model (e.g. spawning behaviour of the different age classes). The variation of simulated survival according to spawning distribution was examined on a multi‐annual scale and showed a coherent pattern with past and present stock structures. The interaction processes between the population (influence on spawning) and its environment (influence on survival) and its implications on recruitment and stock dynamics are discussed.     

Biophysical modelling of larval drift, growth and survival for the prediction of anchovy (Engraulis encrasicolus) recruitment in the Bay of Biscay (NE Atlantic)

Fish recruitment is the result of the integration of small‐scale processes affecting larval survival over a season and large oceanic areas. A hydrodynamic model was used to explore and model these physical–biological interaction mechanisms and then to perform the integration from individual to population scales in order to provide recruitment predictions for fisheries management. This method was applied to the case of anchovy (Engraulis encrasicolus) in the Bay of Biscay (NE Atlantic). The main data available to investigate survival mechanisms were past growth (otolith) records of larvae and juveniles sampled at sea. The drift history of these individuals was reconstructed by a backtracking procedure using hydrodynamic simulations. The relationships between (real) growth variation and variations in physical parameters (estimated by hydrodynamic simulations) were explored along the individual trajectories obtained. These relationships were then used to build and adjust individual‐based growth and survival models. Thousands of virtual buoys were released in the hydrodynamic model in order to reproduce the space–time spawning dynamics. Along the buoy trajectories (representative of sub‐cohorts), the biophysical model was run to simulate growth and survival as a function of the environment encountered. The survival rate after 3 months of drift was estimated for each sub‐cohort. The sum of all these survival rates over the season constituted an annual recruitment index. This index was validated over a series of recruitment estimations. The modelling choices, model results and the potential use of the recruitment index for fisheries management are discussed.     

Critères de diagnostic des phases d'explosions démographiques et de déclin chez Arvicola terrestris scherman. Exemple de la population du Jura français1

Suite à une étude diachronique d'élements de cinétique d'une population locale (Sombacour, Doubs, France) d'Arvicola terrestris scherman, il semblait possible de fonder le diagnostic de la phase de croissance du cycle de pullulation de cette espèce sur le simple examen de l'évolution numérique des effectifs des populations. Afin de vérifier cette hypothèse a l'échelle régionale, un réseau d'observation a été mis sur pied par le Service de la Protection des Végétaux de Franche-Comté et couvre, depuis octobre 1983, 80 communes du Doubs et du Jura. Il a permis de déclencher une alerte agricole de façon rationnelle et graduellement dans l'espace et le temps, en octobre 1985, avril 1986 et octobre 1987. Une analyse comparative de certains critères morphologiques et de l'intensité du flux de dispersion dans deux situations (la premiere en phase de forte densité du cycle de pullulation, la seconde en phase de déclin) a permis d'échafauder une méthode opérationnelle qui demande confirmation et permettrait le diagnostic fondé de la phase de déclin.     

Tests d'efficacité en nature de produits rodenticides à l'encontre d'Arvicola terrestris scherman. Doit-on s'orienter vers des tests de stratégies de lutte?1

L'élaboration de protocoles de tests en nature de produits rodenticides conduit régulièrement à se poser la question de la reproductibilité des expériences et de la validité de la comparaison des résultats obtenus par diverses équipes travaillant indépendamment. Ces comparaisons ne sont rationnellement possibles qu'à condition de prendre en compte les éléments de la biologie de l'espèce (place de l'expérience dans les cycles annuels et pluriannuels) et ceux du milieu (paysage, passé cultural). Ceci met en évidence le problème plus vaste de la variabilité de l'efficacité des traitements en fonction des facteurs évoqués ainsi que de la rémanence et des effets cumulés de traitements. Le protocole expérimental proposé dans cet article est loin de remplir toutes les exigences requises par un tel test, mais en constitue une approche.