Une campagne de prélèvements réalisée en 1999, de façon comparable à celle effectuée en 1994, montre que la compositiondes communautés d'oligochètes et de Chironomidés a changé dans cet intervalle de temps en réponse à la baisse des concentrationsen phosphore dans l'eau du Petit Lac, le bassin ouest du Léman (Suisse et France). Les larves de Chironomidés étaient présentesdans 66 % des 159 sites visités en 1999 contre 40 % en 1994 tandis que l'abondance des oligochètes a diminué. De plus,l'abondance relative des taxons indicateurs de conditions oligotrophes (Micropsectra et Spirosperma velutinus) a augmenté en1999. Ces changements indiquent qu'en 1999 la restauration biologique des sédiments profonds se trouve à mi-chemin entrel'état méso-eutrophe des environs de 1980 et l'état oligotrophe d'avant 1950. Cependant, l'ampleur de la restauration n'est pas lamême dans les trois bassins du Petit Lac: elle varie en fonction de l'intensité de la sédimentation organique.

A new corer is described which may be used in sediments of shallow standing waters, such as in rice fields, and which facilitatesthe study of the vertical distribution of the invertebrate fauna at 2 cm depth intervals. Its small surface area permits quantitativesampling of the sediment-dwelling fauna, particularly the chironomid larvae, around the roots of rice-plants. Results arepresented and the efficiency of the sampling method is discussed.

Four samples of pupal exuviae of Chironomidae (Diptera) were collected from 8 sites of the Ourthe basin from April 1994 to August 1994. These collections were used to determine normal seasonal trends. The samples yielded a total of one hundred and seven species. Seveteen are new to the fauna of Belgium with a possible additional three taxa (*). A taxonomic list of the species with locations, ecological features and periods of sampling is given, in a table which allows comparison with previous checklists.

A study of the Chironomidae (Díptera) of the river Meuse and two of its tributaries (Sambre and Samson) during the period 1991 to 1992 resulted in a list of one hundred and twenty species. Thirty one of these (*) are new records to the Belgian fauna. A taxonomic list of the species with locations is given.

Les diatomées de l'épilithon et les chironomidés du benthos ont été utilisés pour évaluer l'impact de pollutions sur la Garonne par les effluents d'une papeterie (Saint Gaudens) et par les rejets d'origine domestique et industrielle (Toulouse). L'indice chironomidien (ICh) est plus stable dans le temps et paraît refléter la qualité globale moyenne de la rivière. L'indice diatomique (IPS) fluctue dans le temps et reflète plus précisément les impacts ponctuels des pollutions. Les valeurs moyennes de l'IPS sont légèrement supérieures à celles de l'ICh mais les deux indices réagissent d'une manière similaire à une dégradation de la qualité de l'eau. Des mesures biologiques complémentaires doivent être envisagées pour une appréciation plus fidèle de la qualité des systèmes lotiques.

Pupae and pupal exuviae were collected by drift and hand netting from 27 sites on 10 streams in the Sierra Nevadamountains in 1986 and 1987. The sites represented an altitudinal range from 340 m to 2100 m. The pupal exuviae collections revealed a composite fauna of 143 species. Eukiefferiella (12 spp.) and Tvetenia (3 spp.) were dominant both taxonomically and numerically along most of the altitudinal profile, followed by Cricotopus (11 spp.), Orthocladius (9 spp.) and Diamesa (7 spp.). The altitudinal distribution of the 99 most common species is shown and compared with those obtained in other Europeanstreams or rivers, especially in the Pyrenees. The general pattern of altitudinal zonation shows an increase in speciesrichness from the headwaters (< 2000 m : 58 spp.) toward the middle reaches (1000-1600 m : 121 spp.). The theoreticallyexpected highest species richness in the foothill reaches (> 1000 m : 113 spp.) was not obtained. The periods of reduced or intermittent flow, the domestic organic inputs and the narrowness of the channels in the foothill reaches appear responsible for the decrease of the species richness of the chironomid communities.

Sublittoral and profundal chironomid community structure, depth distribution and relationship to the trophic level of the waters were investigated in Lake Vico (Central Italy) during 1985-1986. PCA analysis indicated a depth-dependent group of true profundal stations at 20, 30 and 40 m depths, characterized by Micropsectra, Procladius, Microtendipes, Tanytarsus and Paratendipes, and a group of 10 m stations, characterized by Cryptochironomus, Polypedilum bicrenatum gr., Cladopelma lateralis gr. and C. laccophila gr., representing the sublittoral features of this depth. In agreement with the chemical data, the chironomid community indicated a mesotrophic condition of Lake Vico, with a tendency towards an increasing trophic level in the deepest zone. A significant role in revealing future trophic changes in the lake may be attributed to the key-indicator Micropsectra.

A review of present information on the zoogeography of Chironomidae at subfamily and generic levels is given. The known distribution, including some previously unpublished records, of all recognisable genera (307) and subgenera (56) is tabulated according to zoogeographical region. The greatest number of genera is known from the Nearctic (202) followed by the Palaearctic (187), Neotropical (109), Australasian (107), Afrotropical (104) and Oriental (100). The chironomid fauna of each zoogeographical region is discussed and a comparison of the number of known species and percentage representation of each subfamily for each region is given. An account of the distribution and ecology of each of the ten subfamilies is included. To date, some 3 700 species are described representing only 30 % of the estimated world chironomid fauna. The fossil record of the group is briefly discussed and the Chironomidae are estimated to be at least 200 million years old dating back to the Triassic period.