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Abstract :
[en] Due to the expected climate changes, it is predicted that disease-carrying mosquitoes will expand their geographical range, resulting in increased use of larvicides (insect growth regulators or IGRs) to face their proliferation. Among IGRs, the pyriproxyfen (PXF) is widely used and has been shown to prevent larvae from developing into adults and thus rendering them unable to reproduce. However, because of a similar endocrine system between crustaceans and insects, PXF could also impact aquatic crustaceans. In addition, when spreading in the environment, PXF is found in a mixture with other pollutants such as metallic trace elements, which could alter its action.
Consequently, the present work was devoted to analyse the PXF effects on the growth hormonal pathway of the freshwater amphipod Gammarus pulex, as well as the combined binary effects with cadmium (Cd). After 7 days of exposure, concentration of the methylfarnesoate hormone (MF) was assessed, as well as the relative transcriptional expression of the farnesoic acid O-methyltransferase (FAMeT) (enzyme limiting the MF production), the methoprene-tolerant receptor (Met), known to bind MF to activate some transcription factors, such as broad-complex (BrC).
Results revealed that exposure to PXF decreased the MF concentration, although an increase of FAMeT expression was measured. Besides, Met and BrC expressions were also increased suggesting the activation of the hormonal pathway. Nonetheless, the presence of Cd seemed to suppress these effects and even to achieve to opposite effects. Indeed, Cd-PXF binary exposure caused the diminution of MF concentration as well as under-expressions of FAMeT, Met and BrC.
This work confirmed that PXF single exposure could impact non-target organisms such as amphipods through changes in hormonal pathway of methylfarnesoate. Nevertheless, when PXF was mixed to Cd, opposite results were obtained, suggesting different consequences on the long-term of the amphipod growth.
