Ecology of the chironomidae (Diptera) in some gravel and sand pits

The chironomid faunasof several gravel and sand pits in Staffordshire and Buckinghamshire were investigated. The sites were chosen to reflect a cross-section of the lake types created by the aggregate extraction industry and were also of varying age. Emergence traps were operated in 1975/76 on a 39 year old gravel pit and showed a markedly different fauna from that described by workers on other lakes. Subsequent analysis of the benthic communities shows that the pits studied possess a fairly uniform fauna which can be divided into two groups related to water depth and age: this classification does not divide the pits on the basis of their location. Despite the uniformity of the fauna it is noted that the assemblages contain few species. The distribution pattern and feeding behaviour of the abundant species were investigated at three stations in one lake and it was found that larval distribution is related to feeding habits both at the microhabitat level and in the lake as a whole. The colonisation of new pit habitats was investigated using a series of purpose-dug ponds. Developing midge populations were monitored by larval and emergence sampling and reveal the speed and replicability of colonisation. It is noted that after two years the pond community structure was similar to that of a much more mature area. The dispersive ability of adult chironomids is dependent upon successful dispersal of fertilized females to new habitats. The distribution and activity of adults shows a clear sex-dependent dichotomy based upon the roles each sex performs. The morphological dichotomy is countermanded in mermithid infested individuals of Einfeldia dissidens such that all parasitised individuals are feminised. The management of wet gravel and sand pits for various recreational uses is considered. In particular the relationship between the chironomid emergence and duckling growth and survival in these lakes is discussed