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Abstract: The authors investigated in this paper the attractiveness of a water colonized (‘positive’ breeding site) or not (‘negative’ breeding site) by larvae of Aedes aegypti on gravid females and then characterized their physicochemical properties to identify and quantify the principal components. The results showed that the water that sheltered several generations of larvae was more attractive to gravid females than water that had never been colonized. The water in a ‘positive’ breeding site contains 2.5 times more ammonium ions (NH+ 4), four times more nitrite ions (NO− 2) and 20 times more nitrate ions (NO− 3) than ‘negative’ breeding water. The authors suggest that in the ‘positive’ breeding sites, where the larvae absorb the organic matter, the turbidity of water decreases, which makes it possible for organic nitrogen to be converted into nitrites and nitrates via the nitrifying activity of the bacteria (NH+ 4 →NO− 2 →NO− 3). It is likely that chitin, while accumulating and decomposing at the bottom of the breeding site, may increase the percentage of organic carbon and ammonium ions, then reinforcing the nitrification process. Conversely, in the ‘negative’ breeding site where the conditions of evolution of the nitrifying bacteria are more restrictive, the nitrogen remains primarily in its organic form. To cite this article: F. Darriet, V. Corbel, C. R. Biologies 331 (2008). [Copyright &y& Elsevier]

Marine microorganism activities are commonly assessed by bulk methods and assigned to the total cell count. The presence in significant amounts of ghost, dead, and damaged cells makes such an assignment a non-correct one. A Nucleic Acid Double Staining protocol (NADS) of fresh water bacteria (Barbesti et al., Cytometry 40 (2000) 214–218) has been adapted to resolve viable, damaged and dead cells in marine environments (Gre´gori et al., Appl. Environ. Microbiol. 67 (2001) 4662–4670). The present paper reports the first in situ application of this approach, conducted in the Bay of Marseilles in winter and spring periods at two sites with contrasted features. To cite this article: G. Gre´gori et al., C. R. Biologies 326 (2003). [Copyright &y& Elsevier]