Lutte biologique et écologie spatiale
    Biological control and Spatial Ecology
April 2014
Forest and urban insects

Dispersal and Allee effects in Ips typographus (Service Public de Wallonie (DGARNE) — 2007-2013)

img Our working hypothesis is that Ips typographus disperses widely upon emergence, each individual joining an existing "reservoir" in the air, fuelled by a large number of sources. Once a new piece of resource has been located by a foraging male, this latter emits pheromones to attract females, and other males, "spying" on the first male, also land on the newly discovered host.
A minimal population threshold is thus required to ensure collective discovery and exploitation of new resources. As a consequence, in the absence of a "reservoir" (i.e. when multiple sources do not exist), an imported population would be unable to establish because its member would disperse so widely that they would be unable to locate each other anymore. In other words, Ips typographus is probably an extremely poor invader, in spite of the forest damage that it can create in its area of endemicity.

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Here, we study the spatial process of establishment along a 200 km transect startingfrom an area (Belgium, Bouillon) where Ips typographus is endemic and ending in an area (Châlons-en-Champagne) where the beetles are absent. Trapping sites are established every ten kilometer along the transect and comprise each ten pheromone traps which are visited monthly.
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Fresh host material is also deployed along the transect, to allow correlating local population density (estimated from the trap catches) to establishment capacity (estimated from the gallery densities on the logs). At the Ips-free end of the transect (forêt domaniale de la Perthe), infested logs are brought in the spring and the capacity of the imported population to reconstitute itself is measured by recording beetle establishment on fresh unattacked logs placed radially at 10 m distance increment from 0 to 50 m from the infested pile.

Contact: J.-C. Grégoire

Surveillance et protection phytosanitaire de la forêt wallonne (Service Public de Wallonie (DGARNE) — 2004-2013)

img The forests of Wallonia (ca 600,000 ha) are, as any other forests in the world, threatened by animal pests and diseases, both native or exotic.
LUBIES has been co-operating with the Walloon Region since the early nineties to contribute to forest health, in partnership with the Walloon Agricultural Research Centre (Dr Anne Chandelier and Dr Michel De Proft).
Different questions have been tackled: ecology and control of Ips typographus, establishment of survey methods and of a risk model for Ips typographus, a feasibility study for the establishment of an Observatory of Forest Health in Wallonia, a list of exotic species threatening the Walloon forests.
A database of predicted risk of I. typographus infestation has been made available as part of this project and can be accessed (in french) here.

Contact: J.-C. Grégoire
Collaborators: S. Aron (EBE, ULB); J.-L. Deneubourg (USE, ULB)

Impact of past climate changes on the genetic diversity of phytophagous insects characterized by a Eurasian arctic-alpine distribution (Fonds de la Recherche fondamentale collective FRFC — 2009-2012)

This project is coordinated by Dr Patrick Mardulyn (EBE, ULB). It aims at establishing a comparative phylogeographic study of different phytophagous insect species (four leaf beetles and two bark beetles) which are all characterized by an arctic-alpine distribution range. Through a comparison of the phylogeographic patterns of these species with different molecular markers, we expect to identify characteristics common to these different species. The dispersal strategies of the six species are very different, and we are analysing the influence of these strategies on the distribution of genetic diversity over the whole range of each species. By analysing genetic variation (e.g. using coalescence models) we will test hypotheses regarding the past population history of the species studied and, more generally, we expect to develop a better understanding of how past climatic oscillations have influenced biological diversity.

Contacts: F. Mayer & J.-C. Grégoire
Collaborator: P. Mardulyn & M. Quinzin (EBE, ULB)

Individual and collective issues in dispersal and aggregation: from proximal causes to ultimate consequences at contrasting scales (Communauté française, Research funding Programme — “Concerted Research Actions”) — 2010-2015; and PDR, F.R.S.-FNRS -2010-2014)

This project links three teams at ULB: the Unité d'Ecologie sociale (USE), the Evolution biologique et Evolution lab (EBE) and LUBIES. It is coordinated by Dr Jean-Louis Deneubourg (USE, ULB).

Dispersal strategies are strongly related to resource distribution and to the unpredictability of the environment. Many patches characterized by different parameters coexist on the dispersal zone. These parameters are more or less easily detectable by each individual and modulate its probability of leaving/joining. A fundamental problem for the animals is the discovery or the selection of the most rewarding patch. In the case of social species, the interplay between the individual capabilities, the social interactions and the patch distribution leads to complex situations. Concerning individual dispersion, mechanisms based on amplification and preventing scattered settlements play a key role. Settled individuals can attract conspecifics and/or stimulate them to stay on the patch. Increased local density may lead to various forms of cooperation but to summarize, it is crucial for individuals to maintain high density or to reach critical density.
In this general framework, we focus our study on the poorly studied aggregation strategy based on conspecific attraction. In insects, evaluation of the number of conspecifics relies on cues that are the result of the modification of the environment or of the release of a chemical or physical marker, operated by the conspecifics. We assume that one function of area marking by settled individuals is to produce public information about patch suitability. Consequently, the trend for an individual to stay and settle on a patch will increase with the marking intensity. This highlights the fact that global behaviours can be generated through competing amplification processes and limiting factors in which individuals follow a few simple decision rules.
Three model systems are studied: i) dispersal strategies and aggregation in cockroaches (USE); ii) Host-trees as patches - how tree resistance generates a particular foraging strategy in a spruce bark-beetle (LUBIES); iii) Allee effects in ants, and how they modulate founding success and space occupancy.

Contact: J.-C. Grégoire
Collaborators: J.-L. Deneubourg (USE, ULB); S. Aron (EBE, ULB)