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Large pine weevil

Large pine weevil, Hylobius abietis, is a major pest on tree seedlings planted on clear-felled conifer forest sites. The large pine weevil is a serious pest of conifer forests across Northern Europe, wherever clear-felled sites are replanted.

Adults are attracted to the stumps of newly felled conifers, in which they lay their eggs. Development takes place under the bark of the tree stumps. Emerging adults feed on the bark of newly planted seedlings (both conifer and broadleaf) which they can kill.

What are the symptoms of the damage caused by the large pine weevil?

Adult weevils feed on the bark of young trees used for restocking. Heavy feeding results in ring barking and eventual death of the tree.

What are the economic consequences of the large pine weevil?

Pine weevil Hylobius abietis is the most dangerous pest of restock areas. Where chemical insecticides are used, there are costs associated. For example in Ireland, the cost  of pre-treatment of plants and of treating planted plants in Coillte forests was an average of €1.6 million over the five years from 2009 to 2013 inclusive. Killed trees need to be replaced; for example replacement after failure of treatment costing up €300,000 per annum.  In other countries such as Poland, seedlings are not protected against pine weevil which causes the death of up to 45% of seedlings.  Each year, it affects more than 10.000 ha of forest plantations in Poland and the total cost of seedling replacement is estimated at €5.000.000 per year.

How can the large pine weevil be controlled?

Protection of seedlings with chemical insecticides for up to two years after planting. An alternative method for pine weevil suppression is the application of entomopathogenic nematodes to tree stumps harbouring developing pine weevils.
Weevil management strategies can be based on reducing the number of weevil grubs developing in the stumps (applying insect-killing nematodes), planting before or after weevil numbers peak (‘hot planting’ or leaving a site fallow), or protecting seedlings even when weevil numbers are high (chemical insecticides and mounding).

Use of pesticides

Problems associated with plant protection chemicals include residues in the environment, impact on non-target organisms and the health of forest workers. Many European forests are managed according to the principles of Sustainable Forest Management which embraces the policy of reducing chemical use.  The use of chemicals to manage pine weevil is one of the greatest uses of chemicals in forest management.

BIOCOMES biological control agent

The reduction of chemical plant protection products on the EU market, resulting from the implementation of Directive 91/414, Directive 2009/128/EC and Regulation 1107/2009, led to the elimination of many pesticides recommended to forest protection. On the other hand, there are no alternative methods that effectively limit the extent of damage caused by large pine weevil. For these reasons, there is a need to develop biological methods, as a part of integrated methods of large pine weevil management.
Entomopathogenic nematodes (Steinernema and Heterorhabditis) are lethal parasites of insects that actively seek out and kill insects in soil and other cryptic media. They have widespread natural occurrence but, to control pests, populations are augmented by inundative application of mass-produced nematodes.

Photo: Picture: Gyorgy Csoka, Hungary Forest Research Institute, Bugwood.org

Christine Griffin
Christine Griffin
Large pine weevil and fungal root rot diseases
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Biological Control Agents

At the end of the project strains of entomopathogenic nematodes will be available that are capable of seeking out and killing pine weevil stages developing underground in tree roots and stumps. The nematodes will be applied in liquid formulation. Recommendations for use will be developed.

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Current stage of the Biological Control Agent

75%

Month 36: Results from small-scale field trials on efficacy of various EPN species against pine weevil in different forest soil types and under moisture-limited conditions
Month 48: Report on persistence of EPN in forest soils and effects on non-target organisms, and protocols for EPN application against pine weevil in different European bioclimatic zones

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