The use of larvae and pupal exuviae to study the biodiversity of Chironomidae in Mediterranean streams

A total of 100 larval and 101 pupal taxa were found belonging to 60 and 36 genera, respectively, in 25 river sites in Catalonia (NE Spain). If we correct for the total number of individuals examined (7629 larvae, 1589 pupal exuviae) the number of genera per 100 individuals is 0.84 for larvae and 2.26 for pupal exuviae and the number of taxa per 100 individuals 1.40 and 6.10, respectively. The following points explain why a similar number of taxa have been found for larvae and pupae (despite the large difference in the number of genera): i) difficulties in differentiating the larvae species, especially in some complex rich and frequent genera, such as Cricotopus-Orthocladius (only six taxa as larvae but 31 as pupae); ii) many (24) larval genera were not found as pupae (even two subfamilies) while only three genera where found only as pupal exuviae. This is because of the larger number of larvae examined, but also because not all the larvae present at one site had emerged at the time of sampling. Given the difficulties in classifying the larvae to species level, the collection of pupae remains a useful method to complement quantification of chironomid biodiversity in a region; until massive DNA-sequencing of field samples of such invertebrates will be possible and easily available to many researchers (especially those in low income countries).