Nematodes to control the large pine weevil
Hylobius abietis is a very destructive pest of conifer restocking sites throughout Northern Europe, and if left uncontrolled it causes significant economic losses. Repeated field trials by Forest Research UK have shown that applications of Steinernema carpocapsae to the soil surrounding conifer stumps infested with H. abietis results in consistent and significant reductions in weevil emergence; at least equal to other tested nematodes. Contrary to its ambusher classification, S. carpocapsae was shown to be as motile as the intermediate S. feltiae and cruiser Heterorohabditis megidis in forest substrates, but in sand it was far less motile. These data suggested the perception that S. carpocapsae is relatively sedentary has resulted from testing motility in inappropriate substrates. Further experiments showed that all tested entomopathogenic nematodes, including S. carpocapsae, showed strong positive thigmotaxis to long distance seismic vibrations through peat; a response to a cue never before documented in insect parasites. In addition, when chemical gradients were compromised, all tested nematode species could still follow vibrational clues, implying that with increasing soil organic matter the utility of host chemical cues declines. The results also suggested that seismic vibrations are potentially less prone to interference from the soil matrix than chemical signals. These data facilitated rejection of the hypothesis that S. carpocapsae does not respond to long-range host cues. A field experiment established that the good field performance of S. carpocapsae was not due to an increased capacity for field survival of this nematode. The cruise foraging, locally isolated S. kraussei was less efficacious than S. carpocapsae against H. abietis, yet persisted in the soil for longer.