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The diet of Harpagtjer bispinis (Pisces:Nototheniidae) from two localities of the South Shetland Archipelago was studied. Simultaneous to thecapture of H. bispinisand at the same sites the availability offood was considered, and amphipod diversity was compared with the density of Harpagifer. It was found that three quarters of the fish fed only on amphipods (mainly Gondogeneia antarctica) and for the rest amphipods were also the main component, even when other prey species were available. The high selectivity of G. antarctica is due to its high mobility and to the fact that Harpagtjer is an ambush feeder. At different predator densities the amphipod fraction of the community appears to be highly modified by the predator both numerically and in species evenness. We postulate that Harpagifer can be a key species in structuring the mobile epibenthic community, even when this environment is subject to strong physical stress.

SYNOPSIS Caloric values, .ash and hydricpercentages \Vere obtain. ed f70m the most abundant benthic invertebrates of Corral Bay, from which this information was not previously available. The range of these values is not different to tho~ of related taxonomic groups of other OCeans. A nnual fluctuations of these paramenters \Vere studied in Mytüus chilensis so as to obtain a qúant(tatlve estimation of the variation of the!e values.

Up to now, the search for an efficient artificial diet to rear the predator Eriopis connexa, native to the Colombian highlands of Cundinamarca and Boyacá has been without success. Therefore, it is necessary to determine which of the available preys supply the best food for its development, survival and fertility. With this purpose, under controlled conditions, three aphid species, accessible within the natural habitat of the predator, were evaluated. The cabbage aphid (Brevicoryne brassicae) does not provide an adequate nutrition for the predator, and apparently, the glucosinolate content of this aphid is transferred and affecting the predator. Based on the demographic parameters such as net reproductive rate, finite reproduction rate, generational time and intrinsic growth rate, for three consecutive generations, it was determined that none of the other two aphid species can be considered either as optimum prey. Macrosiphum euphorbiae, as prey stands out over the alder aphid, Pterocallis sp., supplied as food. The influence that these three prey species had on the growth potential of the larval stages of the predator, under particular ambient conditions, is reported.