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The Society of Environmental Toxicology and Chemistry (SETAC)² is the most important international scientific society dealing with environmental chemistry and toxicology. This year's SETAC award for the best publication in risk assessment, modelling and theoretical studies was given to INRA-Rennes doctoral student, Claire Duchet. The award is in recognition of an article published in 2010 in the Ecotoxicology journal that resulted from a part of her doctoral research. The award aims to recognise young scientists and is often bestowed upon doctoral students.
In France, most mosquito control is carried out using larvicides. Claire Duchet's work tested the methods assessing the environmental impact of two natural products in Atlantic and Mediterranean coastal wetlands. The first product, Bti (Bacillus thuringiensis serovar israelensis) is essentially the only bioinsecticide used in France to control mosquito larvae. The second product, spinosad, belongs to a new class of products called naturalytes. Already available for sale in the United States, spinosad is being tested for release in France as an alternative to Bti. Interest in spinosad has been generated not only by its natural origin but also its unique mode of action, different to Bti's.
When a single product is used, as is the case in France with Bti, the development of resistance becomes possible. Mosquito control programmes must therefore have access to a variety of products to counter this risk. However, Bti's mode of action is associated to four toxins acting on four different targets and, as a consequence, specialists feel that the risk of Bti resistance is low.
Population-level impact of spinosad’s toxic effects on the individual
The work carried out by Claire Duchet and her colleagues demonstrates that Bti remains the larvicide with the most satisfactory environmental profile. Importantly, it highlights spinosad's poor ecotoxicology profile and raises questions as to its use in the natural environment and its benefit as a potential larvicide in France.
To evaluate the environmental impact of these two products, Claire Duchet concentrated her research on two different Daphnia species found at the study sites: Daphnia pulex in the Gulf of Morbihan and Daphnia magna in the Camargue.
Daphnia pulex (Crustacea, Cladocera), egg-bearing female.
© Gérard Balvay, INRA
Commonly known as water fleas, Daphnia are small crustaceans well known to ecotoxicologists as sentinel species. These small planktonic feeders are indicative of water quality and are key organisms in the aquatic environments where they are found. As primary consumers, they form the base of the food chain, further reinforcing their role as ecological indicators. By studying Daphnia in a variety of conditions, such as laboratories, micro- and mesocosms and natural environments, scientists are able to rapidly gather information on the ecological risk to food chains.
Claire Duchet used two types of experiments to compare the effects of exposure to the two bioinsecticides on the Daphnia. Laboratory experiments demonstrated that spinosad had an effect on individual performance in terms of survival, fertility and reproduction in both Daphnia species studied, whereas no effect was observed in individuals exposed to Bti.
In the field, Duchet observed that spinosad exposure resulted in a rapid dying off of Daphnia populations. Under certain conditions, when the dose of spinosad was low, populations were able to recover. These observations were made with the help of a unique tool: the microcosm – small enclosures that allow naturally present Daphnia to be isolated on site. They allow experiments to be carried out in the natural environment and to expose the naturally present Daphnia to the insecticides without the risk of environmental contamination.
Evaluating the effects of mosquito control treatments on wild Daphnia populations. Studying field microcosms in Mediterranean and Atlantic zones. © ESE, INRA
Working from her laboratory and field microcosm data on individuals and populations, Claire Duchet conducted a simulation using a population dynamics model. This enabled her to predict Daphnia population trends and, among other things, to evaluate the risk of population extinction once the species were exposed to Bti or spinosad in the wild. Her results confirmed the transfer of toxic effects from the individual to the population and predicted a decline in Daphnia populations.
This young scientist's work could lead to a reliable and repeatable method for use when testing the cumulative unintentional effects of biocide control products for wetland mosquitoes.
Today, Claire Duchet is a part the EID Méditerranée team in Montpellier, a regional body for mosquito control on the French Mediterranean coast. She is continuing to collaborate with Laurent Lagadic on a European Union project assessing the impact of mosquito control products used in France and in France's overseas departments.
(1) An aquatic ecotoxicology specialist, Claire Duchet prepared her thesis under the direction of Laurent Lagadic as a part of the Ecotoxicology and water quality team in the Joint Research Unit for Ecology and Health of Ecosystems (UMR ESE) of INRA/AgroCampus Ouest in Rennes, France.
(2) Setac website
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