L'effet de la salinité (0,3 - 0,45 et 2,45 g.L-1) et de la dureté (250 - 500 g.L-1 (CaCO3) sur la toxicité de Al, Cu, Cr, Cd, Ni, Zn vis-à-vis de Daphnia magna est étudiée en laboratoire. Les concentrations en ions métalliques varient entre 0,01 et 25 mg.L-1. Les résultats obtenus à 20°C montrent que la toxicité mesurée en CI50 24 h et CI50 48 h (CI = Concentration d'Inhibition) de Cd, Cu, Zn et Al augmente avec un accroissement de la salinité ou de la dureté. Par contre, la toxicité de Ni et Cr est atténuée malgré l'accroissement de la salinité du milieu. L'augmentation de la dureté entraîne une réduction de la toxicité du chrome.

Historically, the Kissimmee River meandered over an extensive floodplain wetland. In response to catastrophic flooding and settlement pressures in Central Florida, the Kissimmee was channelized, converting the complex, braided channel into a straightened canal. The result has been a sharp decrease in fringing wetland habitat and associated biota. Soon after channelization was completed, environmental concerns prompted the State of Florida to start examining options for restoration to reestablish the river's natural hydrology and restore lost wetland habitat. The grass shrimp, Palaemonetes paludosus has been identified as a keystone invertebrate species in this system. This study was designed to examine its distribution, diel movement, and growth within the two dominant macrophyte communities of the Kissimmee River riparian marsh: Nuphar and Polygonum. Results indicated that grass shrimp were more abundant in Polygonum beds. This species also showed no well-defined diel migration, although we found a significant vertical pattern in some instances. Palaemonetes paludosus growth was highest on periphyton and Polygonum leaves. Grass shrimp distribution may be explained by their decreased susceptibility to predation because of the higher habitat complexity inherent in Polygonum beds.

The genus Labiobaetis recently has been reported from Madagascar by Lugo-Ortiz and McCafferty (1997). The two described species were only known from the nymphal stage. Examination of material from more than 800 samples in Madagascar allows descriptions of six new species: Labiobaetis longicercus, L. dambrensis, L. nigrocercus, L. vulgaris, L. punctatus and L. gilliesi. They can be distinguished easily by the shape of the second segment of the labial palp, the shape of the second segment of the maxillary palp, the setation of the labrum, the number of gills, the presence or absence of hindwings and coloration of the abdomen. At present, the imagoes of only five of the eight species are known. They can be identified by the presence or absence of hindwings, coloration of the wings, shape of the sclerotized process between gonopods and shape of the third segment of the gonopods. As all the species assigned to Labiobaetis were recently reassigned to Pseudocloeon, the status and validity of the genera Labiobaetis and Pseudocloeon are discussed.

Le genre Setodes est signalé pour la première fois à Madagascar. Cinq espèces nouvelles sont décrites. Les affinités de ce petit groupe relativement homogène sont asiatiques et l'hypothèse d'une colonisation probable de la Grande Île depuis l'Inde est discutée. La répartition géographique et l'écologie des espèces sont analysées en fonction de l'altitude et de la distance de la source.

The chironomid fauna ot the Western part of France has been notably understudied ; few data are available on species distribution for the region. This paper provides some information obtained from several studies conducted in the eastern part of Brittany. Although a small part of this region is considered, the checklist comprises 94 species, four of which are recorded for the first time in France.

Patterns of parasite infestation by plerocercoid forms of the tapeworm Ligula intestinalis (Cestoda, Pseudophyllidea) in the second intermediate host, the roach Rutilus rutilus, were analysed in three fish populations of South-Western France during 1998. In all three studied sites, i.e. Pareloup Lake, Lavernose-Lacasse and Muret gravel pits, roach were commonly parasitized with plerocercoids. A strong increase in prevalence, mean number of parasites and parasitic load was observed in the youngest hosts with a maximum peak reached in the medium-age (2+, 3+)roach classes. Such trends as a function of host fish age would indicate the occurrence of parasite-induced host mortality, with the most heavily infected fish specimens being removed from the three roach populations. The three roach populations infected by L. intestinalis exhibit different patterns of parasite-induced mortality which could correspond to different possible ecological and evolutionary responses associated with local variation in host-parasite interactions. The parasite-induced host mortality observed, i.e. direct mortality caused by pathogenic effects and /or enhanced fish predation by piscivorous birds to increase parasitic transmission is discussed within the context of the adaptative parasite-induced manipulation hypothesis.