The effect of the herbicide mecoprop on Heliscus lugdunensis and its influence on the preferential feeding of Gammarus pseudolimnaeus

Exposure of the aquatic hyphomycete Heliscus lugdunensis to the herbicide Mecoprop did not significantly affect production of the antigen recognized by the specific monoclonal antibody NG-CF10. Therefore, an ELISA method, developed in a previous study, could be used to quantify the biomass of H. lugdunensis colonizing leaves exposed to this herbicide. Exposure to Mecoprop significantly reduced the mycelial biomass associated with alder leaves. This was shown to be a threshold response rather than a dose response, with higher biomass recorded on control leaves. No significant differences were found over the range of Mecoprop concentrations used. In laboratory experiments, Gammarus pseudolimnaeus was offered a choice of alder leaves exposed to a range of Mecoprop concentrations. The animals were able to discriminate between the exposed and control leaves, and between inoculated and sterile leaves. Presence of the fungus resulted in increased leaf consumption, but no interaction between the Mecoprop concentrations and fungal colonization was observed. The major factor affecting food choice was the concentration of Mecoprop that the leaves were exposed to-not the Mecoprop-mediated effects on fungal biomass.