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Improving protection and resistance of forests to the spruce aphid

Contract nr: FAIR-CT96-1792
Project nr: 1792
Project type: SC
Starting date: 01/03/1997
Duration: 40 months
Total cost: 1,951,000 EUR
EC Contribution: 1,579,000 EUR
Scientific Officer: Alkmini KATSADA
Research topic: Afforestation, sustainable management of forests, integration of functions, agro-forestry
Acronym: Resforaphid

The green spruce aphid (Elatobium abietinum) is a ubiquitous and debilitating insect pest of spruce forests in Europe, causing widespread defoliation and reductions in tree growth and timber production. Evidence assembled by AIR3-CT94-1883, suggests that although these impacts are likely to intensify in the future, the pest problem could be alleviated by introducing pest resistance into tree improvement programmes, by simple and cost effective silvicultural measures to encourage natural biocontrol, and by taking into account genetically differentiated forms of the pest in parts of Europe, where new forests are becoming established.
Day,K.R., Halldórsson, G., Harding S. and Straw N. (1998) The Green Spruce aphid in Western Europe: ecology, status, impacts and prospects for management. Forestry Commission Technical Paper, 24 HMSO, London, 105 pp.

The key objectives are to:

1) define the contribution that genetic variability of the pest will make to pest problems in the future;
2) determine the characteristics of forest which are related to effective biocontrol of the pests by natural enemies;
3) seek novel, sustainable solutions to the depression of pest population density through habitat manipulation and augmentation of natural enemies;
4) identify the nature of resistance in Sitka and Norway spruce by investigating individual and population responses of the pest to spruce genotypes with different levels of resistance;
5) characterise spruce resistance in terms of chemical, anatomical and genetic markers and firmly establish the basis for a selection programme for resistance;
6) identify the responses of spruce genotypes to defoliation and thus the advantages of selecting resistance traits in the timber industry;
7) estimate the impact of defoliation events on final tree size and timber production;
8) develop models for pest populations and their biotic and abiotic interactions, which will allow the joint evaluation of resistance and biocontrol;
9) determine through cost-benefit analyses the advantages of using resistance and natural enemy augmentation, for wood and fibre production and the costs of more aggressive pest genotypes;
10) recommend optimal solutions to the pest problem and strategies for safeguarding forest production levels in Europe.

Measures to augment biocontrol will be investigated through detailed studies of the functioning of biocontrol in plantation forests and by reference to biodiversity data. Simulation models for biocontrol will be developed here, and their use extended to incorporate the results from tasks dealing with aphid and plant genetic differentiation. For the latter, work will focus on understanding the mode of action and consequences of plant resistance to the pest. Markers for spruce resistance will be sought among terpenes and phenols and by DNA analyses. The results from DNA analysis will be combined with empirical field data to calculate genetic parameters for the heredity of resistance. Economic gains for resistance and biocontrol will be studied by parameterisation and calibration of forest stand growth models which will provide a firm framework for estimating management costs/benefits. This multidisciplinary study relies on the complementary expertise of seven research institutions in five Member States and will represent a landmark study in integrated pest management for forests in Europe.

Current situation/results:
The project will be completed in June 2000.
Studies on the aphid in Iceland have offered the opportunity to track the genetic diversity of the pest, introduced relatively recently to a new forest region. Research has now shown that Icelandic aphids arise from distinctive lineages which are demarcated geographically. The possible bionomic differences in aphid lineages and consequences for the regional development of the pest problem are being analysed.

Natural enemies, particularly predatory coccinellids, had a significant impact on patterns of aphid abundance. Their absence from plantation forests in parts of Europe may have profound effects on the pest problem. There is a consistent range of species present from among the most important predatory arthropod types in most forest regions, although some species were absent at higher latitudes. Seven species of pathogenic fungi (Entomophthorales) have been identified from field populations in north-western Europe, and these may contribute to control. Simulation models of aphid-natural enemy interactions provide real insights into the effectiveness of biocontrol in different forests. Studies within and between forests locally show marked differences in predator abundance and suggest that silvicultural management which augments natural enemies may significantly reduce aphid populations.

Field experiments, replicated for consistency between years, have highlighted differences in the performance of aphids on a range of Norway and Sitka spruce clones. Two particular Sitka spruce clones show low reactions to aphid attack. For Norway spruce, biochemical analysis of the clones reveals consistent differences in the concentration of terpenoids for trees which are low aphid-producers. Some biochemical components can be regarded as markers for resistance. The consistency of aphid resistance on Sitka spruce is high and tolerance is carried through at least two generations of trees. Heritability estimates of needle loss between families were 0.72 (p<0.0001) and, together with large variations in defoliation, this is expected to lead to large gains by breeding. After screening 170 RAPD-primers representing 700 polymorphic loci, two loci have been identified as co-segregating with field resistance within each of two investigated families of Sitka spruce. The two RAPD markers are able to explain 55 and 80% respectively of the within-family phenotypic standard deviation in field resistance. Such findings open up the possibility of performing marker assisted selection in the progeny and, with further work, substantial improvement in resistance is within reach.

Experiments have demonstrated clear morphological and phenological differences between the spruce genotypes tested and provide some evidence for variation in aphid/needle loss relationships, indicative of differences in genotype resistance. A counter-intuitive result has been that tree growth is better correlated with aphid numbers than foliage loss, suggesting that aphids have a direct effect on spruce. Simulations produced by the plantation growth model suggest that a regular 25% defoliation of the older needles has little effect on tree size at harvest. In contrast, trees subjected to 100% defoliation of older needles are likely to show a marked reduction in stem mass. Cost analyses of the aphid problem have been based on a range of economic and biological assumptions. One set of reasonable assumptions, including 75% defoliation of crops every six years (a common pattern), suggests a loss of nearly 20% income at harvest. Some models of resistance and biological control of the pest reduce this loss significantly.

Jensen, J.S., Harding, S., Roulund, H. (1997) Resistance to the green spruce aphid (Elatobium abietinum Walker) in progenies of Sitka spruce (Picea sitchensis (Bong) Carr.). Forest Ecology and Management 97:207-214.

Skov, E. and Wellendorf, H. RAPD markers linked to major genes behind field resistance against the Sitka spruce aphid Elatobium abietinum in Picea sitchensis. Forest Genetics, in press.

Sigurdsson, V., Halldórsson, G., Sigurgeirsson, A., Thórsson Æ.Th., and Anamthawat-Jónsson, K. (1999) Genetic differentiation of green spruce aphid (Elatobium abietinum Walker), a recent invader to Iceland.

Agricultural and Forest Entomology, 1: 157-163.

Straw, N.A., Fielding, N.J., Green, G., Coggan, A. (1998) The impact of green spruce aphid, Elatobium abietinum (Walker), on the growth of young Sitka spruce in Hafren Forest, Wales: pattern of defoliation and effect on shoot growth. Forest Ecology and Management,104: 209-225.

Straw, N.A., Fielding, N.J., Green, G. and Price, J. (2000) The impact of green spruce aphid, Elatobium abietinum (Walker), and root aphids on the growth of young Sitka spruce in Hafren Forest: effects on height, diameter and volume. Forest Ecology and Management, in press.


Keith DAY
University of Ulster
Environmental Studies
Cromore Road
UK-BT52 1SA Coleraine
Tel.: +44 028 7032 44 47
Fax: +44 028 7032 49 11


  • Gudmundur HALLDORSSON
    Iceland Forest Research Station
    IS-270 Mosfellsbaer
    Tel.: +354 566 60 14
    Fax: +354 566 77 50

    Norwegian Forest Research Institute
    Høgskoleveien 12
    N-1432 Ås
    Tel.: +47 64 94 89 93
    Fax: +47 64 94 29 80

  • Nigel Allan STRAW
    Forestry Commission
    Alice Holt Lodge
    UK-GU10 4LH Wrecclesham - Farnham
    Tel.: +44 1420 222 55
    Fax: +44 1420 236 53

  • Simon Robert LEATHER
    University of London
    Imperial College of Science
    Technology and Medicine
    Silwood Park
    UK-SL5 7PY Ascot
    Tel.: +44 1344 29 43 16
    Fax: +44 1344 29 43 08

    Université Josepf Fourier
    Rue de la piscine 2223
    B.P. 53
    F-38041 Grenoble
    Tel.: +33 4 76 51 42 78
    Fax: +33 4 76 51 42 79

  • Hans ROULUND
    Royal Veterinary and Agricultural University
    Kirkegaardsvej 3A
    DK-2970 Hoersholm
    Tel.: +45 35 28 36 30
    Fax: +45 35 28 36 29

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