Introduction. The severe impact of papaya bacterial canker in the West Indies justified launching a program to transfer the genetic resistance/tolerance identified in local germplasm to good-quality cultivars. As a first step, a germplasm collection from the Caribbean was gathered and its morphological and genetic diversity assessed. Materials and methods. The total sample included 50 accessions from the Lesser Antilles, Cuba, Venezuela, Costa Rica and Hawaii. Morphological data from a subsample of 29 accessions were submitted to analysis of variance, principal component analysis and Neighbor-Joining cluster analysis. Nine isozyme systems were tested, and the corresponding data were processed for cluster analysis and genetic parameters, including the fixation index, diversity indices and heterozygosity. Results. Eighteen of the 47 Caribbean and Venezuelan accessions exhibited hermaphroditism. Venezuelan accessions displayed the widest morphological diversity, while those from Barbados were distinguished by fruit quality. Sexual type affected leaf and flower traits. Cluster analysis shows little morphological differentiation between origins, with the relative grouping of the accessions from Guadeloupe or Barbados. Only four isozyme systems were polymorphic, producing 34 distinct zymotypes, with a relatively high heterozygosity and a particular diversity in Venezuela, Guadeloupe and Barbados. Geographic structuration appears limited in the cluster analysis among individuals; however, it is clearer when considering the six best-represented populations, with one cluster representing Venezuela, Trinidad and Barbados, and one for Guadeloupe, Martinique and Grenada. Discussion. The low level of fixation is attributed to dioecy and to the low level of selection. The relative isolation of island populations has favored geographic differentiation, albeit limited. The differentiation between the good-quality germplasm from Barbados and the tolerant populations from Martinique and Guadeloupe encourages the development of a marker-assisted introgression scheme.

Zooplankton samples were collected over a 21-month period in five floodplain lakes of the Orinoco River in orderto establish zooplankton species composition, abundance patterns, and biomass and their relationships with the patterns of inundations and lake morphometry. 60 rotifer taxa were identified. This group was generally more abundant thancopepods and cladocerans (mean : 73,4 % of total zooplankton). Common and abundant rotifer species included K. americana, K. cochlearis, B. mirus, B. gessneri, P. vulgaris and F. longiseta. Copepods were dominated by nauplii (mean : 73,8 % of total copepod stages). Cladocerans were scarce and dominated by M. minuta, C. cornuta and D. spinulosum.Most frequent and abundant zooplankton species were euplanktonic with a dominance of filter feeders and microphagous detritivores. Mean zooplankton density in all lakes ranged from 340 ind./l to 3 486 ind./l. Biomass ranged from 71,1 µg.l (dw) to 432,8 µg/l. Rotifers accounted for 64,7 % of the total mean zooplankton biomass in three lakes whilecopepods accounted for 57,8 % of the biomass in two lakes. Both density and biomass were markedly seasonal withhighest mean values at low waters. Mean density in the lakes was 100 times higher than in the Orinoco main stem. Lakeswith highest variabilities in surface area and water depths showed highest zooplankton densities. The type of connection (direct or indirect) established between the lakes and the major source of the water also seemed important to interpret the productivity of floodplain lakes.

The compositon, abundance and biomass of the benthic fish fauna were studied along a 6 km stretch of the GuariticoRiver. This water course is located in the western plains of Venezuela and belongs to the Apure River floodplain system.Monthly collections from June, 1990 to January, 1991 were made by means of a small trawling apparatus rigged todugout canoes according to the design of López-Rojas et al. (1984). 42 fish species were identified with a dominanceof species from the orders Siluriformes and Gymnotiformes. The fish assemblage differed markedly from other Venezuelan river systems. Seasonally, higher diversity and evenness were observed at the high water phase while the abundance, relative biomass and CPUE were higher at low water.

Stomach content analyses were performed on dwarf specimens of Asplanchna sieboldi collected on different dates in a shallow floodplain lake of the Orinoco River system. The results showed that the dwarf forms of A. sieboldi were highly selective on small Brachionids (Brachionus caudatus and Keratella americana). This observation confirmed on the carnivore status of these forms of the species. Considering the aleatory character of prey capture in rotifers, the high selectivity observed in A. sieboldi may be controlled by the abundance of the favoured small-sized prey. Under the conditions of the study, Asplanchna may be considered a stenophagous predator. The prédation pattern exhibited by the dwarf A. sieboldi under our tropical conditions was similar to the pattern exhibited by larger species of Asplanchna in temperate regions. In both regions, size and abundance of prey seem to control the food preferences of this planktonic predator.

Plusieurs specimens de Camptocercus du Rio Uracoa (nord-est du Vénézuéla) ont été identifiés à Camptocercus australis var. dadayi décrit de Colombie par Stingelin (1913).Sur la base de l'étude morphologique des individus vénézuéliens et des données de la littérature, le statut de ce taxon, d'abord rattaché à la forme australienne (australis), puis à la forme paléarctique (lilljeborgi) de Camptocercus, est discuté.L'ensemble des caractères propres aux populations sud-américaines permet de les séparer des formes australienne et paléarctique, et de leur attribuer un rang spécifique.

L'examen de 110 échantillons pélagiques et de 16 échantillons littoraux de plusieurs corps d'eaux du bassin moyen de l'Orénoque (lac de barrage, lacs d'inondation du système Orénoque et Caroni, rivières) a permis d'identifier 58 taxa de Cladocères, dont 24 sont nouveaux pour la faune vénézuélienne. 2 espèces, Alona ovata et Bosminopsis macaguensis, sont nouvelles pour la science. Alona karelica, élément paléarctique, n'avait jamais été mentionnée sur le continent américain.35 % de la faune étudiée sont représentés par des formes néotropicales, dont 8 endémiques sud-américaines.Une partie taxonomique illustrée est consacrée à 13 espèces rares ou peu connues.La répartition des espèces dans les milieux prospectés et dans les deux catégories d'eaux blanches et d'eaux noires,a été étudiée. La faune la plus riche de Cladocères a été observée dans les lacs d'inondation de l'Orénoque, la diversité spécifique étant due aux formes littorales appartenant principalement à la famille des Chydoridae.En milieu pélagique, les corps d'eaux blanches sont caractérisés par l'association Moina minuta, Ceriodaphnia cornuta, Bosmina tubicen, Bosminopsis deitersi, les corps d'eaux noires par la dominance des Bosminidae : Bosmina hagmanni, Bosminopsis macaguensis, Bosminopsis deitersi, Ceriodaphnia cornuta. Le cas de Daphnia gessneri, généralement considérée endémique du système Amazone-Orénoque et présente dans un seul relevé, est discuté.

La femelle parthénogénétique de Leydigiopsis ornata Daday, 1905 est redécrite. Des données morphologiques complémentaires incluant l'étude détaillée des appendices thoraciques sont fournies. La femelle éphippiale et le mâle, inconnus jusqu'ici, sont également décrits. Les caractères morphologiques différentiels des 4 espèces du genre sont discutés.

Deux nouvelles espèces de Cladocères ont été découvertes dans du matériel pélagique et littoral de plusieurs corps d'eaux du bassin moyen de l'Orénoque. Bosminopsis macaguensis n. sp. est régulièrement présente dans le peuplement pélagique de Macagua, lac de retenue sur le fleuve Caroni, affluent de l'Orénoque. La population est comparée à une des populations de Bosminopsis deitersi qui colonisent les autres milieux pélagiques de cette région. La comparaison est effectuée tant au niveau des mâles que des femelles. Alona ovata n. sp. a été récoltée dans la zone littorale d'un lac du système d'inondation de l'Orénoque. Elle se distingue de toutes les autres espèces du genre par la forme et l'armature du post-abdomen.