Nestmate recognition in three species of stenogastrine wasps (Hymenoptera,Vespidae)

The capacity to recognise a conspecific intruder was investigated in Parischnogaster jacobsoni, Liostenogaster flavolineata and L. vechti, three species of primitively social wasps of the subfamily Stenogastrinae. Results of behavioural experiments carried out in the field showed that females of all three species react pacifically if presented with female nestmates, but aggressively reject an intruder from a conspecific colony. As L. flavolineata and L. vechti both build large clusters of nests, often very close to each other, the recognition capacity among females from different nests, but in the same conspecific cluster, was also investigated. Females of both species were more aggressive towards females from a different colony in the same cluster than towards their female nestmates. Additional experiments on L. flavolineata showed that there was no difference in reaction towards females from colonies nearer or further from the tested colony but within the same cluster, nor towards females from a different cluster. The capacity to recognise an alien conspecific nest containing immature brood was investigated in P. jacobsoni. Adult females of this species, invited to land on an alien nest which had experimentally been exchanged for their own, accepted the new nest and partially destroyed the immature brood. The behaviour of the females when they land on an alien nest, however, suggests that they do recognise the nest as foreign. Acceptance of foreign nests coupled with low immature brood destruction is probably due to the high energetic costs of egg-deposition and larval rearing in stenogastrine wasps. These results suggest that nestmate recognition in these wasps is very efficient, even though they belong to the most primitive subfamily of social wasps. Received: 16 April 1996/Accepted after revision: 9 August 1996     

The changing state of contamination in the Lagoon of Venice. Part 1: organic pollutants

The Lagoon of Venice is a transitional environment suffering from industrial, urban and agricultural impact. Recently the mechanical clam fishing, preventing a regular deposition of sediments has made sampling of cores suitable for radiodating very problematic. Therefore, in this study, in order to assess temporal and spatial trends of contamination, the same sampling scheme was repeated three times over a 12-year period. The concentrations of PCBs, PAHs and organochlorine pesticides were measured in the uppermost 5 cm of sediments collected in 25 sites in the central portion of the lagoon during three campaigns conducted in 1987, 1993 and 1998. Analytical results, validated statistically, indicated that, while PCB and pesticide concentrations tend to decrease during the considered period of time, PAH do not, showing that the input rate of these compounds to the lagoon environment is still important. A spatial trend of pollution was also found in the lagoon for PCBs and pesticides, which decrease from the sources, namely the industrial zone and the mouths of rivers, to areas closer to the sea: a reduction up to 80% and 90%, respectively, was monitored. PAH contamination, originating chiefly from incomplete combustion of fossil fuels, as inferred from ratios of congeners, was mainly located around the historical center of Venice, where most of the boat traffic is concentrated and has an increasing trend.