Dispersal and host-finding ability of entomopathogenic nematodes at low temperatures

To enhance the control of sedentary, subterranean insect pest species like Otiorhynchus sulcatus, 19 new alpine isolates of entomopathogenic nematodes were screened for infectivity at 9°C. For this purpose, nematode dispersal was studied in the presence of late instar Galleria mellonella and O. sulcatus, using a T-tube choice system filled with moist sand. For each isolate five characteristics were recorded: migration rate, average distance travelled, host-finding ability, parasitisation rate, and invasion rate. As expected, most isolates accumulated in the host compartments. The rank sum of the isolates, calculated according to the ranks attained for each of the five characteristics, classified seven Steinernema kraussei before the first S. feltiae. However, no single isolate was clearly the most infective. Steinernema sp. 1, Heterorhabditis CH-H-FLU91, and the commercially available S. feltiae OBS III yielded lowest scores. They are considered unsuitable control agents at low temperatures. The locomotory activity of the nematodes in dispersal assays with G. mellonella was significantly correlated with their efficacy at 8.5± 1°C against O. sulcatus in pot experiments. This indicates that T-tube choice experiments as performed in this study represent a meaningful tool for selecting cold-active nematodes. In supplementary dispersal experiments with larvae of Melolontha melolontha, biological control-performance of the four nematode species tested was meagre.