How far do you go? Stable isotope analysis reveals the dispersal abilities of larval and adult click beetles in arable land

Click beetle larvae within the genus Agriotes feed on roots and tubers of plants and are serious pests worldwide. Albeit highly relevant for the control of these insects, the dispersal abilities under natural conditions of both larvae and adults are poorly known. Here we used a stable isotope approach to assess the dispersal abilities of agrioted beetles in arable land. To examine dispersal of adult beetles, pheromone traps were installed at two study sites in Tyrol (Austria), each comprising a maize field and adjacent C3-grasslands. The different 13C signatures of these plants are reflected in the larvae and this signal is translocated to the wing covers of the adult beetles. Hence, adult beetles which developed in maize fields and moved into adjacent grasslands can be identified by their 13C signature. Similarly, the dispersal abilities of the Agriotes larvae can be examined, which was done in another experiment comprising both maize and C3-crops. Beetles covered distances of at least 80 m beeline and up to 13 % of individuals caught in traps at 80 m distance from the maize field showed 13C signatures of the maize plants. However, no larvae with non-crop specific signatures were found in the adjoining crops. These findings show that adult Agriotes are capable to migrate over larger distances than previously assumed, whereas the horizontal dispersal of the Agriotes larvae is more restricted.