Exploring the Ecological Impacts of Bti on the Dynamics of Chironomid Communities

Investigating the ecological consequences of Bti, Nina and her team’s study exposes surprising parallels in chironomid responses, challenging existing assumptions.

“Our recent scientific publication analyzed the ecological consequences of Bacillus thuringiensis var. israelensis (Bti). Bti is a commonly applied mosquito control agent in the Upper Rhine area and is, due to its target-specificity, assumed to be environmentally friendly. However, the effect on communities of closely related insects, such as chironomids, is still unknown, despite their crucial ecological role in riparian ecosystems. The study was a joint effort: Three PhD students from the SystemLink graduate school along with their supervisors conducted the planning, sampling, laboratory work and data analysis of the mesocosm study. The EERES Team played a crucial role in supporting the sampling efforts on the EERES mesocosm facility, while numerous student helpers from the iES were involved in sorting of samples. Additionally, Jonathan Jupke from the working group Quantitative Landscape Ecology provided invaluable expertise to facilitate the model-based evaluation of the generated data.

For our study, which was conducted over a 16-week period spanning spring and summer of 2020, over 30.000 chironomid individuals were sampled right after their emergence from the mesocosm ponds. Half of those ponds had been treated with Bti during the development of the chironomid larvae. The aim was to map the relationships between the occurrence or abundance of different chironomid genera and the application of Bti.

Using cutting-edge methods like DNA metabarcoding and Hierarchical Modelling of Species Communities (HMSC), we explored how Bti affected the chironomid communities (Figure 1). Surprisingly, the different chironomid genera responded similarly to Bti, challenging previous assumptions about the role of their larval feeding strategies and phylogenetic affiliations. Both taxonomic and genetic diversity positively correlated with the number of emerged individuals, revealing a connection between biodiversity and emergence. Furthermore, our investigation extended to the impact of Bti treatment on the body size distribution of the emerging chironomids. The results hinted at potential consequences for predators such as bats and spiders that might selectively target certain prey sizes.

Figure 1 Graphical abstract of our new study “How non-target chironomid communities respond to mosquito control: Integrating DNA metabarcoding and joint species distribution modelling”, published 2024 in Science of the Total Environment.

This collaborative venture not only expands our understanding of how human activities impact ecosystems but also showcases the power of interdisciplinary teamwork in science. The participation of researchers from various backgrounds, including ecotoxicology, molecular ecology, ecological modelling and fieldwork expertise demonstrates the strength of collaborative efforts in ecological research.

For those eager to explore the full story, the complete paper can be found here: https://authors.elsevier.com/a/1iOUaB8ccylk3. It’s available for free reading and downloading until February 27, 2024 — no registration required. We hope you enjoy the read!”