Control of a major pest of forestry, Hylobius abietis, with entomopathogenic nematodes and fungi using eradicant and prophylactic strategies

Hylobius abietis, a major problem for seedling survival on forested land, develops under the bark of stumps of felled conifers. We investigated the efficacy of entomopathogenic nematodes (EPN) and fungi (EPF) applied to stumps to suppress adult emergence. We performed five field trials over three years and assessed results through destructive sampling and emergence trapping. We used two strategies in application: eradicant, where treatments were applied after weevil colonisation and prophylactic, where treatments were applied prior to colonisation. At prophylactic sites no treatment significantly reduced weevil emergence. At all eradicant sites, treatments including nematodes were more efficacious than those not. EPF-only treatment did not significantly reduce weevil emergence compared to controls, but there was a non-significant (P = 0.058) numerical reduction at one site. The effects of EPF and EPN were additive. There was evidence of mortality due to native Beauveria sp. at all three eradicant sites, identified as Beauveria caledonica at one. A proportion of weevils at depths of up to 18 cm in the soil were infected by the applied Beauveria bassiana showing that applied fungi can reach this cryptic pest. If choice of EPF strain and application technologies are optimised, EPF may present a viable control method for pine weevil in the future.