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SUMMARY 1. Methanogenic carbon can be incorporated by methane-oxidising bacteria, leading to a 13 C-depleted stable carbon isotopic composition (d 13 C) of chironomids that feed on these microorganisms. This has been shown for the chironomid tribe Chironomini, but very little information is available about the d 13 C of other abundant chironomid groups and the relationship between chironomid d 13 C and methane production in lakes. 2. Methane flux was measured at the water surface of seven lakes in Sweden. Furthermore, fluxes from the sediments to the water column were measured in transects in two of the lakes. Methane fluxes were then compared with d 13 C of chitinous chironomid remains isolated from the lake surface sediments. Several different chironomid groups were examined (Chironomini, Orthocladiinae, Tanypodinae and Tanytarsini). 3. Remains of Orthocladiinae in the seven study lakes had the highest d 13 C values ()31.3 to )27.0&), most likely reflecting d 13 C of algae and other plant-derived organic matter. Remains of Chironomini and Tanypodinae had lower d 13 C values ()33.2 to )27.6& and )33.6 to )28.0&, respectively). A significant negative correlation was observed between methane fluxes at the lake surface and d 13 C of Chironomini (r = )0.90, P = 0.006). Methane release from the sediments was also negatively correlated with d 13 C of Chironomini (r = )0.67, P = 0.025) in the transect samples obtained from two of the lakes. The remains of other chironomid taxa were only weakly or not correlated with methane fluxes measured in our study lakes (P > 0.05). 4. Selective incorporation of methane-derived carbon can explain the observed correlations between methane fluxes and d 13 C values of Chironomini. Remains of this group might therefore have the potential to provide information about past changes in methane availability in lakes using sediment records. However, differences in productivity, algal d 13 C composition and the importance of allochthonous organic matter input between the studied lakes may also have influenced Chironomini d 13 C. More detailed studies with a higher number of analysed samples and detailed measurement of d 13 C of different ecosystem components (e.g. methane, dissolved inorganic carbon) will be necessary to further resolve the relative contribution of different carbon sources to d 13 C of chironomid remains.

SUMMARY 1. The larval chironomid community was studied quantitatively in three cross-sections of an impounded area of the River Danube between July 1985 and July 1986. 2. Sixty-six species were identified, most of which belonged to the subfamily Orthocladiinae, but species of the tribe Chironomini were numerically dominant. 3. The sections differed distinctly in terms of species number and diversity; a tendency towards increasing species richness and diversity was observed in the upstream sections of the impoundment. Marked fluctuations in these two parameters characterized the area close to the dam; the temporal oscillations in diversity values differed significantly between the sections (ANOVA: P

SUMMARY. The drift of chironomid egg masses was investigated in the River Mole (Devon) and the River Wye (Powys) in 1981. Large numbers of egg masses were found in the drift just after dusk; on one occasion an estimated 50,000 egg masses passed a sampling point in 5 h. Oviposition of free-floating egg masses appeared to be initiated and synchronized by the onset of darkness. Egg masses of some Pentaneurini (Tanypodinae), Tanytarsini and Chironomini (Chironominae) were found in the drift and adhering to submerged stones. Flotation by means of a gas vacuole within the egg mass was observed in the Polypedilum ‘convictum’ group. The gas vacuole decreased in size over 8–11 h and the egg masses sank after 2–3h. Some chironomid egg masses are capable of drifting large distances after oviposition. The implications of sueh drift are briefly discussed in relation to the distribution of chironomid larvae.

SUMMARY. The chironomid fauna of a chalk stream in southern England is described from 1 year's catches of emerging adults and 2 year's quantitative samples of larvae on Common Clubrush, Schoertoplectus lacustris. The number of species in eaeh higher taxon as adult males and larvae on Schoenoplectus were: Tanypodinae, nine and three; Diamesinae, two for both; Orthoeladiinae, 26 for both; Chironomini. twelve and six; Tanytarsini, seven and five, respectively. A total of 66 species was recorded for both life stages. Adult Orthocladiinae were caught throughout the year. Tanytarsini were absent for a few weeks in winter, and Tanypodinae and Chironomini were caught for shorter periods in warmer months. Chironomids 93.5% of the total invertebrates on Schoenoplectus. Life histories are deseribed for seven speeies that formed 91% of the identified chironomids (32% of the total were unidentifiable first and second instar larvae). Four of these life histories appear for the first time. All seven species were multivoltine and had continuous recruitment for part of the year. The species diversity of larvae was mostly in the range 1.5–3.0 and it was determined more by equitability than by species richness. The numbers of chironomids through time were dependent on the weight of detritus on the leaves (r2= 0.69) and the availability of detritus therefore partly controlled their population size.