Emergence patterns of diptera in a chalk stream

An emergence trap was operated for two years on a chalk stream in southern England. AH species of aquatic Diptera except Simuliidae and females of Chironomidae and Psychodidae were identified. Chironomidae formed 97% of the total Diptera and 81 species were recorded. Some of the nine species of Ceratopogonidae were occasionally numerous. No other family was important. Differences in the fauna between years were related to changes in the flow regime. Numbers of both species and individuals of Chironomini and Tanypodinae were notably higher in a severe drought than in more typical conditions. Many species had long flight times which in some cases may have been due to polyvoltinism. A comparison of temperatures in streams in which Chironomidae had been studied in southern England and Germany suggested that more generations could be completed in the more temperate English streams. Neozavreliafuldensis and Paratanytarsus lauterborni were new to Britain and a species of Palpomyia may be new to science.