Evaluating arthropods in bufferstrips in the agricultural landscape: Food availability for amphibians

Beside other causes like pathogens, climate change or ozone depletion the main reason for amphibian population declines in Europe is habitat degradation. More than 50% of the land in Europe is agriculturally used and in the course of the intensification of farming, land clearance and the increasing use of fertilisers, pesticides and heavy machines lead to large-scale environments inappropriate for amphibians. Most European amphibians spend more than 80 % of their life in terrestrial habitats using fields for foraging and for migration between ponds or migration to over-wintering habitats (e.g. forests, hedges). So even if adequate aquatic habitats (breeding ponds) are available, amphibians face threats in their terrestrial habitats like being hurt or killed during ploughing practices, desiccating due to nitrogen fertiliser application or being affected by pesticide applications.

Direct lethal effects of pesticides on amphibians were shown by Relyea (2005) for the herbicide Roundup. But it also can be assumed that also indirect negative effects on amphibians occur like the reduction of amphibian prey availability after insecticide application. In this study we tried to assess in a field trial if a reduction in biomass of potential amphibian prey items after insecticide use occurs and how much the biomass is reduced.
We applied a single field rate of Karate Zeon (7.5 g a.i./ha; a.i.: lambda-cyhalothrin, pyrethroid) on 32.5 ha of winter rye fields. Ponds were lying within the fields and were surrounded by 20 m wide extensive used grass strips. We sampled the arthropods in these buffer strips and the neighbouring fields and grouped them into potential food items for specific amphibians.

In total about 40,000 arthropods were sampled with a biomass of about 3000 g. No drift effects in off-crop habitats (shore areas and grass strips) could be observed. The in-crop biomass of prey items for juveniles and adults of the Common Spadefoot Toad was significantly lower on treated fields than on untreated fields during the first week after application. Similar results were also obtained for adult Moor Frogs and adult Fire-bellied Toads and based mainly on significantly lower biomasses of carabid beetles and spiders on the treated fields. Within the first week after application the lowest biomasses during the whole study period were measured on treated as well as on control fields. The reason for the overall reduction of biomasses was probably the cold and rainy weather during this sampling period resulting in low arthropod activity. But as the median biomasses on treated fields decreased up to 6 times as much as on untreated fields, we conclude that the significantly lower biomasses on treated fields occurred mainly because of insecticide effects. E. g. for adult and juvenile Common Spadefoots the reduction of prey item biomass compared to control was 65% within this sampling period.

As assumed insecticide use (shown for Karate Zeon) can significantly lower prey availability for amphibians and may therefore lead to suboptimal foraging conditions.

Poster as presented at the SETAC YES meeting 2009