Food ecology of the wood mouse (Apodemus sylvaticus) : de-husking behaviour and its impact on seed treatment risk assessment

Seed treatments are widely used on cereals and other annual crops throughout Europe. Most of the formulated pesticide is found on the outside of the seed, the husk. Risk assessments of seed treatments are especially needed for granivorous mice living in the agricultural landscape e.g. for registration using the guidance for risk assessment for birds and mammals. The dehusking of seeds before consumption is a known behaviour of these mammals but so far no quantitative data on the reduction of exposure of seed treatments by dehusking were published. Therefore we aimed at providing a first quantitative estimate of this behaviour related exposure reduction for the wood mouse (Apodemus sylvaticus) with different seed types.
We evaluated the efficiency of dehusking behaviour of 20 wood mice captured in the wild for four different seeds (wheat, barley, maize and sunflower). One experimental setup used a fungicide seed treatment where the remaining seed husks of consumed seeds were analysed with a HPLC-MS/MS technique. In the second set up we measured generic pigment present in a blank seed treatment formulation and determined the leftover pigment in the husks with a photometric technique.
The exposure reduction was similar for the fungicide and the pigment design where the same seed types were studied. We could demonstrate exposure reductions ranging from around 60% for cereals to almost 100% for sunflower seeds as a result of the dehusking behaviour.
Since exposure reduction was similar in both approaches working with pigments would be a generic way to estimate the impact of dehusking behaviour on seed treatment exposure. This behaviour can result in a substantial exposure reduction and should therefore be considered in a seed type specific way in the risk assessment of pesticide seed treatments.
It is proposed to include a seed specific dehusking factor in the calculations of estimated theoretical exposure of seed treatments for granivorous mice. The approach of accounting for a dehusking related exposure reduction by field relevant wild mammal species seems a more promising way to advance the risk assessment instead of using generic species and neglecting behavioural traits. The pigment approach could be used to gather data for exposure reduction for other species and seed types. Its advantage is that it is harmless to the test species and comparatively cheap since no chemical analysis is involved.

Related publication

Carsten A. Brühl, Bernd Guckenmus, Markus Ebeling & Ralf Barfknecht (2010) Exposure reduction of seed treatments through dehusking behaviour of the wood mouse (Apodemus sylvaticus). Environmental Science and Pollution Research. (online). DOI 10.1007/s11356-010-0351-x

Bernd Guckenmus, Ralf Barfknecht, Markus Ebeling, Carsten Brühl (2007) Reduction of fungicide concentration by de-husking of seeds by the wood mouse. Poster presentation at the Annual SETAC conference. Show Poster