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

Abstract

a b s t r a c tHylobius 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.

The role of fungus Beauveria bassiana in reducing the number of Pissodes castaneus (Col., Curculionidae) in young forests

“…Wegensteiner and Führer (1988) paid attention to very low mortality of H. abietis beetles attracted to the spruce bark treated with B. bassiana. Williams et al (2013) tried to reduce the numbers of H. abietis larvae developing in the stumps through the application of B. bassiana together with entomopathogenic nematodes (Sterneinema carpocapsae and Heterorhabditis downes) on these stumps. The results showed a higher effectiveness of nematodes (up to 50% mortality of larvae) compared to very low efficacy of fungus (up to 3.5% mortality of larvae).…”

Optimizing the application method of entomopathogenic nematode suspension for biological control of large pine weevil Hylobius abietis

“…Our trials at seven different sites over two years showed that H. downesi gave slightly better results but not significantly different from S. carpocapsae (Kapranas et al 2017), in contrast to earlier work showing that H. downesi was superior (Dillon et al 2006;Williams et al 2013a, b). Typically EPN suspension is applied directly to the soil around the stump (Dillon et al 2006;Williams et al 2013a;Kapranas et al 2017), but in our study we tested a modified method of application by applying the suspension on the top edges of the stump, targeting the gap between the bark and the wood (though some of the suspension will eventually make it to soil by spill over the stump). In the latter method it is likely that some nematodes were more exposed to UV light and desiccation and consequently died but, on the other hand, most of the nematodes entered the space between the wood and the bark and would have transferred, at least to some extent passively, along the rootways, thus reaching more quickly the weevils that are typically found there.…”

“…Traps were sampled every 2-4 weeks throughout the season, starting midJuly until weevil emergence ceased in NovemberDecember. General methods follow established protocols as described for previous studies (Williams et al 2013a;Kapranas et al 2017). …”

“…Biological control of the large pine weevil Hylobius abietis (Coleoptera: Curculionidae) (LPW) using entomopathogenic nematodes (EPNs) has become a feasible sustainable method over the last decade (Torr et al 2005;Brixey et al 2006;Dillon et al 2006Dillon et al , 2007Dillon et al , 2008Williams et al 2013a;Kapranas et al 2017). The LPW is the most important pest of tree seedlings in replanted coniferous forests in Northern Europe (Evans et al 2015).…”

“…In most of the previous trials on the use of EPN, typically nematode suspension is poured in close proximity around the stump (drenching). Previous studies suggest that EPN reach their target, at least to some extent, by passive movement of the suspension liquid (Dillon et al 2006;Williams et al 2013a;Kapranas et al 2017). It has been shown that artificial root-routeways are important for facilitating EPN movement towards their subterranean hosts (Ennis et al 2010) and thus it is reasonable to hypothesize that EPN applied in closer contact with the roots will provide better defence against LPW.…”