The diet of elaterid larvae analysed by stable isotpes

The diet of wireworms (Coleoptera: Elateridae) in arable land and its relationship to soil environmental conditions: A stable isotope analysis Wireworms, the larvae of click beetles (Coleoptera: Elateridae), are abundant dwellers of arable soils. Most elaterid species are thought to be polyphagous in larval stage, feeding on roots, decaying plant material and detritus. Some species, however, are quite serious pests, damaging a great variety of agricultural crops. It is assumed that soil environmental factors (e.g. soil humus and moisture content) and cropping history are the driving factors which determine whether wireworms feed on living plant material or decaying matter. However, under field conditions the relationships between the wireworms` diet and these environmental factors is still open to question. Understanding the parameters which influence the food selection of click beetle larvae would be of basic value to judge the role of specific elaterid species in the soil food web in a correct way. Furthermore this knowledge would be fundamental for the development of any technique to predict wireworm incidence, damage to crops and for their control. A rather new and powerful method to study food webs and trophic relationships is the stable isotope analysis. In the present project this technique will be used for the first time to elucidate the trophic position and connections of wireworms in agricultural land. To interpret the isotopic signatures of the wireworms in a correct way, the field derived stable isotope data are validated by experiments. As samples are gathered from different locations in Central-Europe, comprising a wide range of elaterid species and sites, we will be able to draw a more general picture of the wireworm`s diet in Central-European agricultural land. By correlating the trophic position/diet of the wireworms with humus and soil moisture content of the sites, conclusions can be drawn which of the two variables govern the wireworms` feeding preferences. This will also imply new approaches for the development of control strategies for wireworm damage.

Several species of wireworms, the larvae of click beetles (Coleoptera, Elateridae), can be found in soils of arable land. Many species, especially those within the genus Agriotes, are described as pests which feed on below-ground parts of crop plants such as maize, wheat, and potatoes. The feeding ecology of wireworms under field conditions is, however, poorly understood because there are many methodological hurdles to be overcome before the dietary choices of below-ground invertebrates can be studied. Stable isotope analysis (SIA) offers a new way to investigate trophic interactions in soil animals under natural conditions. This technique was employed, for the first time, within this project to assess the feeding ecology of wireworms in Central European arable land. A series of laboratory experiments revealed how the isotopic signature of a diet is reflected in the wireworm`s tissue addressing the animals` specific life history traits. Based on these results we were able to correctly analyse and interpret the dietary choices and the trophic level of field-collected wireworms as well as to study the dispersal behaviour of these elaterid beetles. Although the herbivorous nature and pest status of Agriotes species could be confirmed, our analysis showed that other abundant wireworm species, previously also classified as herbivorous pests, showed a predominantly carnivorous feeding mode. This calls for reassessing their role in soil food webs and their pest status. Soil organic matter, thought to be an alternative food source for wireworms, was found to play an unimportant role within the diet of elaterid larvae. In contrast, our analysis indicated, for the first time, that weeds are heavily utilized by wireworms as food resources under natural conditions. Thus, weeds (or other plants) might be used to divert the wireworms` feeding pressure away from the main crop to alternative food plants. This is an important finding and will allow creating new sustainable control strategies for wireworms.