Mosquito control

Development of moquito control concepts in conformity with nature conservation

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The Upper Rhine valley is not only a metropolitan area but also one out of 30 “Hotspots of Biodiversity” in Germany. In spring and summer time the river regularly breaks its’ banks and create temporary wetlands having a high floral and faunal biodiversity all along the river Rhine. These valuable landscapes are also protected by designated natural and European protection areas (bird sanctuaries, nature reserves, Natura 2000 sites) that likewise cover a large proportion of the entire Upper Rhine valley. Besides microcrustaceans, insects are the most abundant taxa in seasonal wetlands. Aquatic insects are not only an important food resource for inhabitants of the water body like dragonfly nymphs or amphibians. As imagines they serve as food for terrestrial predators such as birds, bats, spiders and adult dragonflies. The high biomass of mosquitoes (Culicidae) and other midges is not only a food resource for animals but also a nuisance to humans. Therefore mosquito control is widely established in wetlands all over the world. At the moment the most common agent used is Bacillus thuringiensis var. israelensis (Bti), a bacterium producing toxic proteins very specific to the larvae of Nematocera.

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To enhance human comfort the Bti-based mosquito control was originally established in the year 1976 and initiated in an area between Speyer and Karlsruhe. This area enlarged over time up to 350 km along the River Rhine. Each treatment with Bti leads to a reduction of the target organism mosquito of more than 90 %. Depending on the river flood Bti is applied up to 12 times a year. In Germany, Bacillus thuringiensis subsp. israelensis Serotype H14, Strain AM65-52 is registered as "existing active substance" reviewed under the biocide-regulation (528/2012) effective since September 2013.

The application of the larvicide Bti is known as environmentally friendly alternative to other insecticides. However, there are indications that also non-target organisms could be affected by the Bti treatments. The toxic mode of action in the target organism Culicidae is very similar to the mode of action in larvae of Chironomidae which are not the target of Bti-treatments in Germany. These non-biting midges are the most important and abundant food resource in the wetlands for terrestrial and aquatic predators which is why their lack may lead to indirect effects causing changes in the food web. Although direct effects of Bti towards non-target organisms are studied in laboratory and semi-field studies there is a lack of long-term data of indirect effects on non-target species. The current state of knowledge regarding indirect effects is based on just a few long-term studies that show a varied picture depending on the study area. Recently, indirect effects could be recorded for breeding birds in a study conducted in the Camargue region in France. In the year 2013 several master thesis were conducted at the University of Koblenz-Landau referring to this topic. 

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We pursue an interdisciplinary approach of three parts: A mesocosm study, a field study and a socioeconomic evaluation of the affected population using contingent valuation methods. On the basis of the mesocosm approach, we will identify the impact of Bti-treatments on the food availability for predators in wetlands with a special emphasis on the non-target organism Chironomidae. Furthermore, we will increase the knowledge whether the development and the body condition of newts in all stages are indirectly affected by using Bti. A field monitoring in areas with long-term Bti-treatments will serve to evaluate potential indirect effects on ecosystems in the Upper Rhine Valley. To meet the increasing environmental awareness among the population the risk for non-target species has to be included in the evaluation of the socioeconomic benefits related to the mosquito control at the Upper Rhine Valley.

Two doctoral studies are included in the research project. The focus of the first PhD thesis lies on the direct and indirect effects of the Bti-treatment on the non-target invertebrates, so basically biodiversity and ecosystem functions are considered. This doctoral study is funded by research initiative Rhineland-Palatinate AufLand and is part of the Moscofee project. The second doctoral study has the topic "Development of a concept for the mosquito treatments in the Upper Rhine Valley that is in conformity with nature protection" (AZ 32608/01-33) and is funded by the Deutsche Bundesstiftung für Umwelt (DBU).  

Aufland und DBU

 

 A special issue of the Uniprisma dealing with the AufLand project is available here.

 

Related publications

 

Kästel A, Allgeier S, Brühl CA (2017) Decreasing Bacillus thuringiensis israelensis sensitivity of Chironomus riparius larvae with age indicates potential environmental risk for mosquito control. Sci Rep 7:. doi: 10.1038/s41598-017-14019-2

Allgeier S, Frombold B, Mingo V, Brühl CA (2018) European common frog Rana temporaria (Anura: Ranidae) larvae show subcellular responses under field-relevant Bacillus thuringiensis var. israelensis (Bti) exposure levels. Environ Res 162:271–279. doi: 10.1016/j.envres.2018.01.010

Theissinger K, Kästel A, Elbrecht V, et al (2018) Using DNA metabarcoding for assessing chironomid diversity and community change in mosquito controlled temporary wetlands. Metabarcoding Metagenomics 2:e21060. doi: 10.3897/mbmg.2.21060