Notes on the larval taxonomy, ecology, and distribution of the Dutch Chaoborus species (Diptera, Chaoboridae)

In the Netherlands Chaoborus flavicans, C. crystallinus, C. obscuripes, and C. pallidus occur. A key based on larval characters to these Dutch species is given. The validity of the identification characters of the larvae has been tested. It became evident that the place of the seta on the anterior face of the antenna base and the ratio of longest and shortest antennal blades are valuable as a support to other characters only. The shape of the dorsal process and of the anal papillae have identification value, but the labral appendices have not. The head capsule length of the four larval instars of flavicans and crystallinus has been given, but Dyar’s rule does not hold. The distribution in the Netherlands is discussed. All four species can be found in small, shallow waters but only flavicans can be found in large lakes which may either be shallow or stratified. The species all have great ecological plasticity to physicochemical conditions. Flavicans and crystallinus are very common, obscuripes is a little less common, and pallidus is only known from 3 places in our country. Coexistence of 2 or 3 species is the rule rather than the exception.