Jean-Claude Grégoire Honorary Professor

  • +32-2-650.31.70

Jean-Claude graduated in Agricultural sciences and Forestry at the (at the time) Faculté des Sciences agronomiques de Gembloux, and his PhD at ULB was in forest entomology. He was a research associate at F.R.S. - FNRS, then became a professor at ULB. He is now retired but keeps a few things going on.

Research interest

My main field of interest is the ecology, behaviour and control of forest insects. I am particularly interested in their reproductive strategies, natural enemies, relationships to their hosts, and spread. After decades of research, I must conclude that I have probably been ill advised to focus on particular scolytine species, sometimes awfully difficult to rear in the laboratory, instead of concentrating on particular problems to be tackled with easily cultured model species. But, nevertheless, the species I chose to study still fascinate me, as they are exemplary of fully divergent ecological strategies.

A first pet species, Dendroctonus micans is a “parasite” of spruce, whose females are usually fertilized by a brother and establish solitarily of healthy trees, which they do not kill and in which they are protected by the tree chemical and physical defenses against competitors and generalist natural enemies. D. micans is however usually fairly well controlled by a very specific predator, the Monotomid beetle Rhizophagus grandis, and we have actually mass-produced these predators during several decades and released them throughout France with perfect control success. We also have brought a batch of Belgian predators to the UK in the early eighties, in order for the British Forestry Commission to start its own rearing programme, which is still continuing.

A second species of choice, Ips typographus, is the most damaging forest pest in Europe. It regularly kills millions of spruces. It has the fascinating property to be able to shift from a scavenging state, at low population density to a predatory regime, when it kills trees. In both states, the insects behave collectively. When bound to scarce and unpredictable undefended, fallen trees, the young emerging adults disperse widely and search. As soon as a male has found a suitable host, it emits pheromones that attract one to four females but also attract one to four males, as the sex ratio is balanced upon emergence, and as the whole system relies on reciprocal spying. A trade-off of this system is that, because of the density needed in the air for at least one male to discover a tree, the trees are usually colonized at a density higher than the optimal density for maximizing individual brood. When sufficient resources (e.g. a sufficient provision of fallen trees after a storm) have allowed population growth above a certain theshold, and when all the undefended, fallen hosts have been exhausted, the beetles mass-attack living trees, which are colonized at even higher densities than fallen trees, in order to exhaust the tree defenses. Brood production per female is then even lower than on fallen trees, and this could lead to population decline. How this collective behaviour conflicts with individual fitness is an intriguing question indeed, and I am set to explore it further.

A second field of interest for me is pest risk assessment. I am a member of EFSA’s Plant Health panel, and have also been involved in risk assessments for the Belgian National Plant Protection Organization, the European and Mediterranean Plant Protection Organization (EPPO) and for ANSES (FR). I am presently conducting research on the risks for forest trees in Belgium of the pathogenic bacterium Xylella fastidiosa, originating from America and which has been found massively destroying olive trees in southern Italy (Apulia) since 2013 (see the Xyleris project, below). I am also interested in monitoring the presence in Belgium of the agents of the Thousand Cankers disease (the fungal pathogen Geosmithia morbida infecting Juglans spp. and vectored by the bark beetle Pityophthorus juglandis), originating from the US and recently established in central Italy (see the Fungifor project, below).





  • 2017-2018 – Recherche dans le cadre du réseau d’observatoire de la santé des forêts Funded by the Walloon Region
  • 2016-2017 – XYLERIS (Study on Xylella fastidiosa plant hosts and vectors in Belgium and the influence of specific plant growth conditions on disease development) (with UCL, Louvain-la-Neuve, and ILVO, Merelbeke) Funded by the Federal Public Service Health, Food Chain Safety and Environment
  • 2015-2017 - FUNGIFOR (Phytosanitary status of 8 fungi (+ 1 insect vector) infecting trees in Belgium: survey and evaluation of the risk of establishment) (with CRAW, Gembloux, and PCS, Destelbergen). Funded by the Federal Public Service Health, Food Chain Safety and Environment

Past projecst and networks (2010-2017)

  • Recherche dans le cadre du réseau d’observatoire de la santé des forêts (2010-2017) Funded by the Walloon Region
  • LWEC Tree Health & Plant Biosecurity Initiative (Phase 1). Accelerated detection and diagnosis of invasive alien pests and pathogens in imported plants. (2013) Funded by DEFRA (UK)
  • MONOCHAMUS: A study of the Monochamus spp. populations present in Belgium in order to assess their capacity to propagate the pine wood nematode, and to develop preventive control methods (2012-2015) Funded by SPF Santé publique, Sécurité de la Chaîne alimentaire et Environnement.
  • Horizon scanning for new pests and invasive species in Belgium and neighbouring areas (ALIEN ALERT)(2012-2013) Funded by the Belgian Science Policy office
  • Individual and collective issues in dispersal and aggregation: from proximal causes to ultimate consequences at contrasting scales (2010-2015). Funded by the Communauté française Research funding Programme (Concerted Research Actions)
  • Aggregation and dispersion patterns in social insects (2010-2014). Funded by F.R.S-FNRS, Brussels, Belgium
  • COST Action FP1002 - Pathway Evaluation and Pest Risk Management in Transport (PERMIT) (2010-2014). Funded by the COST Programme.
  • ISEFOR (Increasing Sustainability of European Forests: Modelling for Security Against Invasive Pests and Pathogens under Climate Change) (2010-2013). Funded by the EU FP7 Programme
  • Mise au point d’une méthode d’élevage de masse du prédateur Rhizophagus grandis pour la lutte biologique contre Dendroctonus micans (2010-2011). Funded by the Ministère de l’Alimentation, de l’Agriculture et de la Pêche (FR)
  • Impact des changements climatiques du passé sur la diversité génétique des insectes phytophages caractérisés par une distribution eurasiatique arctique – alpine (2009-2012). Funded by F.R.S-FNRS, Brussels, Belgium
  • Methodologie voor risico-analyse ter voorbereiding van de registratie van biologische bestrijders (macro-organismen) - MACROREG (2009-2010). Funded by the Federal Public Service Health, Food Chain Safety and Environment
  • Influence of climatic hazards on beech (Fagus sylvatica L.) susceptibility towards xylophagous scolytines (2008-2011). Funded by F.R.S-FNRS, Brussels, Belgium



Large-scale risk mapping of an eruptive bark beetle – Importance of forest susceptibility and beetle pressure
S. Kärvemo, T.P. Van Boeckel, M. Gilbert, J.C. Grégoire and M. Schroeder.
"Forest Ecology and Management", vol. 318, 2014.


Trees Wanted—Dead or Alive! Host Selection and Population Dynamics in Tree-Killing Bark Beetles
K.L. Kausrud, J.C. Grégoire, O. Skarpaas, N. Erbilgin, M. Gilbert, B. Økland and N.C. Stenseth.
"PLoS ONE", vol. 6, issue 5, 2011.


Coniferous round wood imports from Russia and Baltic countries to Belgium. A pathway analysis for assessing risks of exotic pest insect introductions: Pathway analysis
F. Piel, M. Gilbert, C. De Cannière and J.C. Grégoire.
"Diversity and Distributions", vol. 14, issue 2, 2007.


Predator/prey ratios: a measure of bark-beetle population status influenced by stand composition in different French stands after the 1999 storms
N. Warzée, M. Gilbert and J.C. Grégoire.
"Annals of Forest Science", vol. 63, issue 3, 2006.


Occurrence of Ips typographus (Col., Scolytidae) along an urbanization gradient in Brussels, Belgium
F. Piel, M. Gilbert, A. Franklin and J.C. Grégoire.
"Agricultural and Forest Entomology", vol. 7, issue 2, 2005.


Long-distance dispersal and human population density allow the prediction of invasive patterns in the horse chestnut leafminer Cameraria ohridella
M. Gilbert, J.C. Grégoire, J.F. Freise and W. Heitland.
"Journal of Animal Ecology", vol. 73, issue 3, 2004.


Site condition and predation influence a bark beetle's success: a spatially realistic approach
M. Gilbert and J.C. Grégoire.
"Agricultural and Forest Entomology", vol. 5, issue 2, 2003.

Spatial pattern of invading Dendroctonus micans (Coleoptera: Scolytidae) populations in the United Kingdom
M. Gilbert, N. Fielding, H.F. Evans and J.C. Grégoire.
"Canadian Journal of Forest Research", vol. 33, issue 4, 2003.

Visual, semi-quantitative assessments allow accurate estimates of leafminer population densities: an example comparing image processing and visual evaluation of damage by the horse chestnut leafminer Cameraria ohridella (Lep., Gracillariidae)
M. Gilbert and J.C. Grégoire.
"Journal of applied entomology", vol. 127, issue 6, 2003.


Past attacks influence host selection by the solitary bark beetle Dendroctonus micans
M. Gilbert, G. Vouland and J.C. Grégoire.
"Ecological Entomology", vol. 26, issue 2, 2001.

Spatial distribution of ambrosia-beetle catches: a possibly useful knowledge to improve mass-trapping
J.C. Grégoire, F. Piel, M. De Proft and M. Gilbert.
"Integrated pest management reviews", vol. 6, issue 3-4, 2001.