Using DNA metabarcoding for assessing chironomid diversity and community change in mosquito controlled temporary wetlands (original) (raw)

2018, Metabarcoding and Metagenomics

The biocide Bacillus thuringiensis var. israelensis (Bti) is widely applied for mosquito control in temporary wetlands of the German Upper Rhine Valley. Even though Bti is considered environmentally friendly, several studies have shown non-target effects on chironomids, a key food resource in wetland ecosystems. Chironomids have been proposed as important indicators for monitoring freshwater ecosystems, however, morphological determination is very challenging. In this study, we investigated the effectiveness of metabarcoding for chironomid diversity assessment and tested the retrieved chironomid operational taxonomic units (OTUs) for possible changes in relative abundance and species diversity in relation to mosquito control actions in four temporary wetlands. Three of these wetlands were, for the first year after 20 years of Bti treatment, partly left Bti-untreated in a split field design, and one wetland has never been treated with Bti. Our metabarcoding approach detected 54 chironomid OTUs across all study sites, of which almost 70% could be identified to species level comparisons against the BOLD database. We showed that metabarcoding increased chironomid species determination by 70%. However, we found only minor significant effects of Bti on the chironomid community composition, even though Bti reduced chironomid emergence by 65%. This could be due to a time lag of chironomid recolonization, since the study year was the first year of Bti intermittence after about 20 years of Bti application in the study area. Subsequent studies will have to address if and how the chironomid community composition will recover further in the now Bti-untreated temporary wetlands to assess effects of Bti. This is important as large areas of both aquatic and terrestrial habitats of the Upper Rhine valley are protected (bird sanctuaries, nature reserves and Natura 2000 sites) and comprise of biodiversity hotspots (Biggs et al. 2005, Lukács et al. 2013). However, several studies have shown that Bti non-target effects are possible (reviewed in Boisvert and Boisvert (2000)). Non-biting midges (Chironomidae, Diptera) are the most Bti-sensitive non-target family (Boisvert and Boisvert 2000). Controlled experiments revealed varying mortality rates on chironomid larvae with older larvae