This study investigates a phytophylous community of Chironomidae larvae on the submerged plant species Myriophyllum spicatum L. in a eutrophic lake (Lake Sakadaš, Danube floodplain area in Croatia) during summer 2004. This macrophyte species appeared for the first time in the lake in 2004, lasted approximately three months and was considered as a temporary habitat. The chironomid community was very abundant in the stands of this macrophyte species, which developed at three sites. The recorded species belong to three subfamilies: Chironominae (Chironomini and Tanytarsini), Orthocladiinae and Tanypodinae. Species composition varied in time, though Orthocladiinae with their representative Cricotopus sylvestris gr. dominated throughout the entire sampling period, accounting for approx. 60% of the total community. However, the presence of this species group experienced a marked drop to only 10% in September when Chironomini larvulae and Paratanytarsus sp. prevailed. Furthermore, the share of Endochironomus albipennis (Meigen 1830) in relation to other species was also consistently higher. NMDS ordination and cluster analysis separated three main colonization periods based on larval abundance. RDA analysis indicated the influence of environmental variables, especially Secchi depth, macrophyte dry weight, depth and water temperature, on chironomid community structure.

The diversity of chironomid larvae in relation to flooding and drought phases in a marginal fluvial wetland of the Middle ParanáRiver floodplain was analyzed. Four sampling stations in the right bank of the Tiradero Viejo River towards the interior of themarginal wetland were established: one at the riverside, and three more at 10, 30 and 40 m from the river. Bottom sedimentsamples were extracted during the hydrosedimentological cycle of 2001. A total of 25 taxa of Chironomidae were recorded. Thevalues of taxonomic richness, density and diversity were higher in the marginal fluvial wetland than in the riverside, increasingwhen the wetland is disconnecting from the river. Polypedilum (Tripodura) spp., Polypedilum (Polypedilum) spp., Ablabesmyia(Karelia) spp., Coelotanypus sp., Monopelopia cf. boliekae, Goeldichironomus holoprasinus and Chironomus gr. decorus spp.were dominant in marginal wetlands. The results indicate that the variations in the hydrosedimentological regime, the degree ofdisconnection with the river and the progressive desiccation at each one of the stations of the marginal fluvial wetland arelimitant factors in the distribution and abundance of aquatic chironomids. The different assemblages of Chironomidae werestrongly conditioned by temporal changes related to the gradient of inundation-drought and to the hydroperiod dynamics.