Ecological impact of entomopathogenic nematodes used to control the large pine weevil, Hylobius abietis (Coleoptera: Curculionidae)

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The large pine weevil (Hylobius abietis; Coleoptera: Curculionidae) is one of the most economically damaging pests in forestry across Northern Europe. Its larvae develop in coniferous tree stumps on clearfell sites and adult weevils feed on seedlings that are replanted on these sites, causing substantial mortality. As the drive towards achieving the sustainable management of natural resources increases, biological control agents are being considered as an alternative to chemical pesticides. Though such agents have great potential for contributing towards a reduction in the ecological impact of pest insect control, they must also be investigated for any potentially damaging effects they may have in whichever context they are being employed.
Entomopathogenic nematodes (EPN; Steinernema carpocapsae and Heterorhabditis downesi) are currently being inundatively applied to tree stumps on coniferous clearfell sites in the UK and Ireland as biological control agents against the large pine weevil. The aim of this project was to investigate the risks associated with this use of EPN in this setting. To this end, the persistence of EPN in soil and bark after application to clearfell sites was. Effects of EPN on some important non-target insects on clearfell sites, the service-providing wood decomposer Rhagium bifasciatum and the pine weevil parasitoid Bracon hylobii were assessed via field sampling and laboratory experiments.
EPN presence in soil samples collected around tree stumps on clearfell sites five months, one year and two years after application of EPN decreased significantly from year one to year two. EPN presence on all sites sampled two years post EPN application was relatively low (less than 7 % positive soil samples). A similar trend was observed for EPN persistence under the bark of stumps. No EPN at all were detected two years after application on those sites treated on a small scale by manually applying nematodes. EPN persistence appeared to be better predicted by tree stump species (which in turn is indicative of the number of pine weevils developing within them) compared to soil type. Spread of nematodes was mostly limited to a 40 cm radius around stumps.
The saproxylic beetle community in deadwood other than tree stumps on Irish clearfell sites appears to be dominated by the longhorn beetle Rhagium bifasciatum (Coleoptera: Cerambycidae; Fabricius 1775). Infection of R. bifasciatum with EPN was recorded on three clearfell sites to which EPN had been applied around tree stumps previously. However, since infection of R. bifasciatum overall was low and decreased significantly as the distance between a log and treated tree stumps increased, it appears that the risk to this service-providing non-target insect can be minimised by applying nematodes as accurately as possible.
The ectoparasitoid wasp Bracon hylobii Ratz. (Hymenoptera: Braconidae) is closely associated with the large pine weevil and may therefore be at risk if EPN are applied against the latter (eggs laid on EPN-infected host larvae do not develop to adulthood). Female wasps did not parasitise dead hosts in standard trials (small bark patch [2.25 cm2]; host either freeze-killed or killed by EPN). However, naive wasps parasitised hosts that were moribund (i.e. those that died of EPN-infection within the 24 h period they were offered to wasps) significantly less frequently than either healthy control hosts or infected hosts that survived the 24 h trial period. Experienced wasps (one egg laying experience) parasitised these host types with similar frequency.
Behavioural observations provided no evidence of wasps locating heavily infected or dead hosts and then rejecting them. Heavily infected hosts that died within the 24 h trial period during which they were offered to wasps tended to move less than their surviving counterparts and wasp oviposition was significantly correlated with host movement. Naive wasps were significantly less likely to parasitise hosts that had their mandibles glued shut than those that did not (this had no effect on parasitism by experienced wasps). Both naive and experienced wasps parasitised larvae of R. bifasciatum and G. melonella, hosts types that were different from H. abietis, but that moved during trials. Thus, vibrations caused by host movement and/or feeding seem to be the most important cues for host location and/or host acceptance in B. hylobii. Since naïve wasps took longer and were less likely overall to initiate probing and oviposition during observation, they were less likely to parasitize moribund hosts before these died of EPN infection. This explains why EPN infection affected parasitism by naïve but not experienced wasps. Parasitism of EPN infected hosts by naïve and experienced wasps means that there is a risk of competition between EPN and the non-target parasitoid B. hylobii for H. abietis hosts. However, in a field situation where wasps are likely to encounter several hosts in one host patch and more likely to be attracted to those hosts that are healthy and producing more or stronger vibrational and volatile cues compared to moribund hosts, the extent of competition is expected to be lower than suggested by no-choice laboratory experiments.
In summary, persistence and spread of EPN after application to tree stumps on clearfell sites was low and there was no evidence of a substantial impact on non-target insects. It can therefore be concluded that the overall risks associated with the use of EPN as an inundative biological control agent against the large pine weevil are low.

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Contact Information for This Resource

Dr Christopher Harvey
National University of Ireland Maynooth

Dr Christine Griffin
NUI Maynooth

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Attachment Name and Download Link
Att 1    Spray_rig_treated_sites_persistence_data.xlsx   (0.14 Mb)
Att 2    Bracon_hylobii_experiments_with_H._abietis_larvae_with_glued_mandibles.xlsx   (0.02 Mb)
Att 3    Bracon_hylobii_no-choice_trials_with_behaviour_observation.xlsx   (0.06 Mb)
Att 4    Infection_of_R._bifasciatum_on_clearfell_sites_treated_with_EPN.xlsx   (0.06 Mb)
Att 5    Manually_treated_sites_persistence_data.xlsx   (0.03 Mb)
Att 6   (0.21 Mb)

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Author(s)Harvey, C. Griffin, C.
Title Of WebsiteSecure Archive For Environmental Research Data
Publication InformationEcological impact of entomopathogenic nematodes used to control the large pine weevil, Hylobius abietis (Coleoptera: Curculionidae)
Name of OrganisationEnvironmental Protection Agency Ireland
Electronic Address or URL
Unique Identifier03799dd3-2445-102f-a0a4-f81fb11d7d1c
Date of AccessLast Updated on SAFER: 2024-07-16

An example of this citation in proper usage:

Harvey, C. Griffin, C.   "Ecological impact of entomopathogenic nematodes used to control the large pine weevil, Hylobius abietis (Coleoptera: Curculionidae)". Associated datasets and digitial information objects connected to this resource are available at: Secure Archive For Environmental Research Data (SAFER) managed by Environmental Protection Agency Ireland (Last Accessed: 2024-07-16)


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Access Information For This Resource

SAFER-Data Display URL
Resource Keywordspine weevil, eontomopathogenic nematodes, persistence, biological control, risk assessment
EPA/ERTDI/STRIVE Project Code2007-PhD-B-6
EPA/ERTDI/STRIVE Project ThemeBiodiversity
Resource Availability: Any User Can Download Files From This Resource
Limitations on the use of this ResourceIf the data is to be used in meta-analyses or in any other types of scientific publications or reports, either directly or in reference, please first contact the author for permission.
Number of Attached Files (Publicly and Openly Available for Download): 6
Project Start Date Saturday 1st September 2007 (01-09-2007)
Earliest Recorded Date within any attached datasets or digital objects Wednesday 26th September 2007 (26-09-2007)
Most Recent Recorded Date within any attached datasets or digital objects Monday 30th August 2010 (30-08-2010)
Published on SAFERTuesday 30th August 2011 (30-08-2011)
Date of Last EditSunday 4th September 2011 at 13:09:26 (04-09-2011)
Datasets or Files Updated On Tuesday 30th August 2011 at 15:02:56 (30-08-2011)

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Geographical and Spatial Information Related To This Resource

Description of Geographical Characteristics of This Project or Dataset
The coniferous clearfell sites on which field data in this data set were collected are: Site Site location Kilworth 52°10?N 008°08?W elevation 255 m Featherbed 53°14?N 006°19?W elevation 361 m Raheenkyle 52°18?N 008°34?W elevation 426 m Lackenrea 52°08?N 007°48?W elevation 53 m Ballymac- shaneboy 52°18?N 008°36?W elevation 311 m Deerpark 53°09?N 006°12?W elevation 319 m Oakwood 53°03?N 006°26?W elevation 4 m Glendalough 53°03?N 006°28?W elevation 300 m Glendine 53°05?N 007°34?W elevation 458 m Knockeen 52°12?N 007°10?W elevation 79 m Trees on sites were felled in Dec 2005, except at Featherbed (felled in 2007), Raheenkyle (felled 2006) and Kilworth (felled 2008), Glendalough (felled 2004) and Oakwood (felled 2003). Entomopathogenic nematodes were applied to tree stumps on sites sites in the summer of 2007, except at Featherbed & Raheenkyle (summer 2008), Kilworth (summer 2009), Glendalough (summer 2006) and Oakwood (summer 2005). The soil type, previous stock (i.e. species of the tree stumps on each site) and all other relevant data are given in the respective data sets.

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Supplementary Information About This Resource

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Lineage information about this project or dataset
The aim of this project was to assess the risk that the use of entomopathogenic nematodes (EPN) present to non-target insects and the environment in the context of their use as inundative biological control agents against the immature stages of the large pine weevil, Hylobius abietis (Coleoptera: Curculionidae). Some of the work expands upon that of Dillon et al. and Everard et al. in which the efficacy and persistence of EPN when used against H. abietis and the competition between EPN and parasitoid Bracon hylobii was investigated. The need for risk assessment of EPN as biological control agents in forestry arises since EPN may represent an alternative to chemical pesticides that have been used against the pine weevil to date. In accordance with the target of achieving sustainable forestry, as laid out in the Strategic Plan for Irish forestry (Operational Programme for Agriculture, Rural Development and Forestry (OPARDF, 1999) and by Coillte in the Framework Document for Sustainable Management (1999), the use of biological control methods as opposed to chemical control is desirable, but only if the biological control agents produce less of an environmental impact than the chemical agents previously employed - hence the need for risk assessment of EPN used to control the large pine weevil.
Supplementary Information
The presence of EPN in soil, bark or wood samples was detected by baiting these samples with waxmoth larvae (Galleria melonella). For binomial data, such as that for soil, bark and wood samples (i.e. EPN presence yes or no), infection of R. bifasciatum (yes or no), parasitism of H. abietis and other hosts by B. hylobii (yes or no) etc., a '1' value represents a positive sample and a negative sample is represented by an empty cell or a '0' value.

For details on the wasp and host behaviour, please contact the author. The basic experimental setup for laboratory wasp experiments can be found in:

Everard, A., C. T. Griffin & A. B. Dillon (2009). "Competition and intraguild predation between the braconid parasitoid Bracon hylobii and the entomopathogenic nematode Heterorhabditis downesi, natural enemies of the large pine weevil, Hylobius abietis." Bulletin of Entomological Research 99: 151-161.
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