Chironomus riparius was used to determine whether an increased frequency of chromosome aberrations could be detected in the progeny of an aquatic organism reared in tritiated water (HTO). An increased frequency was detected in larvae whose progenitors had developed either in 250 or 500 μCi/ml of HTO (2500 to 5000 times MPC for occupational exposure). The radiosensitivity of C. riparius to acute gamma radiation was determined and compared with the results obtained with tritiated water. The frequency of aberrations produced by incorporated tritium was approximately the same as the frequency produced by an equivalent dose of chronic gamma irradiation.

Changes in the hydrolytic enzymes, ribonuclease and acid phosphatase were investigated in the salivary gland of Chironomus tentans since these lysosomal enzymes may participate in hormonally stimulated tissue breakdown. Quantitative assays revealed 9- and 12-fold increases in the specific activity of these enzymes during pupation while the protein content of the gland was decreasing. These increases cannot be accounted for by decreased protein but may represent an activation, accumulation, or synthesis which seems to be important in gland breakdown at metamorphosis.

A chironomid population found in a temporary pond in South Dakota and believed to be conspecific with the European Chironomus pallidivittatus was studied. Field and laboratory observations of intraspecific mating behavior are reported. The percentages of females producing viable eggs in crosses of C. pallidivittatus males with females of C. tentons and C. crassicaudatus were 6.2% and 6.3% respectively. In the reciprocal combinations, mating was difficult to induce and no viable eggs were produced. Neither the South Dakota population nor the European species called C. pallidivittatus conform to the morphology of the lectotype.

Glacier brooks in Northern Scandinavia have been investigated for the occurrence of chironomid larvae and pupae. In the uppermost zone of glacier brooks with a very narrow temperature amplitude, Diamesa lindrothi is the most abundant species. In a lower zone with a wide diurnal temperature amplitude during summer months, the simuliid Prosimulium macropyga is more abundant, along with other species of Diamesa. Lacking any primary organic production, the diptera larvae living here feed on particles drifted up on the glacier surface, conserved there and released into the glacier brook by the melting of the ice. The larvae of Diamesa lindrothi have developed adjustments to obviate the strong water current and the instability of the benthic substratum: The mature larvae spin nets over small stone cavities where they live, and thus prevent the pupal stage from being washed downstream. The Diamesa associations in glacier brooks have to be regarded as distinct freshwater biocoenoses. They have to be considered as belonging to the biocoenosis type kryon, and the brooks themselves according to the biotope type kryal. They differ from the krenal and rhithral biotope types by both abiotic and biotic peculiarities, and from the equivalent biocoenosis types by their characteristic life forms and animal associations.