Mosquitoes are rarely popular. Exotic representatives of this insect species are particularly undesirable. However, such mosquitoes are increasingly spreading in Germany due to globalization and climate change − and in addition, viruses transmitted by mosquitoes are becoming more common. The Asian bush mosquito Aedes japonicus japonicus, for example, is a possible carrier of the Japanese encephalitis virus and West Nile virus as well as the pathogens of dengue fever and chikungunya fever.
“To prevent these mosquitoes from transmitting diseases, it may be necessary to control them in the future, i.e. to reduce their numbers. To control the larvae, only the active ingredient Bacillus thuriengiensis israelensis (Bti) is currently available to private individuals. It is considered to be species specific, but is controversial because there are indications that it also kills other animals, such as mosquitoes that are important for the food chain. Additional agents are therefore urgently needed,” says Dr. Friederike Reuss, Senckenberg Biodiversity and Climate Research Center.
Field experiment with clove oil and copper coins
A team led by Reuss therefore conducted a field experiment to test how well essential clove oil and copper in the form of copper tape works against the egg deposition of the Asian bush mosquito in stagnant waters. In addition, the researchers also tested in their laboratory how poisonous one-, two- and five-cent pieces and clove oil containing copper are for the mosquito larvae.
Reuss explains: “Clove oil considerably prevents the egg deposition of Aedes japonicus − the most widespread exotic mosquito in Germany. One gram of clove oil in a cup is enough to reduce the egg deposition in it to a tenth. Moreover, clove oil is poisonous and kills the larvae completely. Copper dissolved from eurocent coins is slightly less efficient against the larvae, but still effective. The two natural remedies would therefore be suitable for reducing a population of Asian bush mosquitoes”.
From field experiments to application − help from the local population is needed
The Asian bush mosquito broods preferably near settlements. There, even small water surfaces in rain barrels, coasters and vases in private gardens and cemeteries offer the mosquitoes the best conditions. “In order to control the mosquitoes, it is therefore important that the local population actively participates and actually uses the remedies in their own gardens,” says Dr. Marion Mehring of ISOE − Institute for Social-Ecological Research.
ISOE researchers under the direction of Mehring interviewed more than 400 gardeners and grave attendants from Hesse, Baden-Württemberg and Rhineland-Palatinate by telephone on this topic. Surprisingly, the majority of participants reject the well-established active ingredient Bti. “Potential users would prefer to use copper-Eurocent coins and essential oils instead of Bti to combat mosquitoes. The respondents would prefer to use copper coins, which practically all of them have in their purse,” says Mehring. A large number of respondents are also willing to implement preventive measures in their daily lives such as covering rain barrels.
Interdisciplinary cooperation to develop environmentally friendly measures
The interdisciplinary cooperation i.e. the combination of ecological and social science research has paid off: With clove oil and copper coins, the researchers were able to identify two agents of controlling Asian bush mosquitoes that are accepted by users and that can now be further developed.
The study is part of the AJAP II research project to develop environmentally friendly measures for the control of the Asian Bush Mosquito. The Senckenberg Biodiversity and Climate Research Center, ISOE − Institute for Social-Ecological Research and the Institut für Arbeitsmedizin, Sozialmedizin und Umweltmedizin of the Goethe University Frankfurt am Main are cooperating in this project. The project is funded by the Fachzentrum Klimawandel und Anpassung of the Hessian Agency for Nature Conservation, Environment and Geology (HLNUG).
Dr. Marion Mehring
Head of Research Unit Biodiversity and People
Phone +49 69 7076919-39
Phone +49 69 7076919-51
Reuss, Friederike/Aljoscha Kreß/Markus Braun/Axel Magdeburg/Markus Pfenninger/Ruth Müller/Marion Mehring (2020): Knowledge on exotic mosquitoes in Germany, and public acceptance and effectiveness of Bti and two self-prepared insecticides against Aedes japonicus japonicus. scientific reports 10 (18901), doi: 10.1038/s41598-020-75780-5