Steinernema kraussei, an indigenous nematode found in coniferous forests: Efficacy and field persistence against Hylobius abietis

More than 100 ha of forest restocking sites in Northern Britain are treated annually with the entomopathogenic nematode Steinernema carpocapsae to control larvae of the large pine weevil, Hylobius abietis. However, data on geographical distribution, thermal niche breadth and foraging strategy suggest that S. carpocapsae may be a poor choice for this application.

We undertook laboratory and field experiments that compared S. carpocapsae with Steinernema kraussei for efficacy towards H. abietis. Steinernema kraussei is indigenous to Northern Britain, active at low temperatures and is thought to adopt a 'cruise' foraging strategy particularly suitable for finding subterranean sedentary insects such as H. abietis. Conversely, S. carpocapsae has not been recorded in Northern Britain, prefers warmer temperatures and is thought to remain at the soil surface adopting an ambush foraging strategy.

There were no differences in the ability of the two nematodes to infect and kill larvae of H. abietis in laboratory experiments and, in two field experiments, both species were equally effective both in terms of parasitizing larvae within the stumps and reducing emergence of adult H. abietis. In one experiment, we monitored persistence of nematodes for 1 year after application and found S. kraussei persistence was much greater than that of S. carpocapsae.

The greater persistence of S. kraussei suggests that this nematode is better adapted to conditions in Northern Britain, but this may potentially represent a greater threat to nontarget insects.

Our data suggest that there would be little benefit associated with substituting S. kraussei for S. carpocapsae in integrated pest management systems for H. abietis.