THÈSE - Université de Franche-Comté

organization for crop protection) surveys the communes and monitors the travelling wave
dynamics of A. terrestris populations for outbreak control. Every commune is scored on a
yearly basis with the following index: 0, no colony observed; 1, some isolated colonies; 2,
colonies present in many pastures and meadows; 3, numerous colonies and serious damage to
grassland. Thus, each parcel was also defined according to the phase of the population cycle
at scale commune.
A TERRESTRIS AND T. EUROPAEA RELATIVE ABUNDANCE ESTIMATION
The estimation of A. terrestris and T. europaea relative abundance on the parcel scale was
based on an index method described in Giraudoux et al. (1995). Such index methods,
calibrated against density estimates based on trapping, are usually employed for large scale
studies (Hansson 1979; Delattre et al. 1999; Fichet-Calvet et al. 1999; Giraudoux et al. 1997;
Quéré et al. 2000). The surface indices used here, were earth tumulus and occurrence of small
mammal holes. A. terrestris presence can reliably be differentiated from T. europaea
molehills. Relative abundance of A. terrestris and T. europaea was determined along a line
that crossed each parcel’s long diagonal. The diagonal was divided into 10 m intervals and the
area observed was 2.5 m on each side of the transect line. Presence or absence of A. terrestris
and T. europaea was recorded for each interval. The relative abundance of both species was
calculated with the following ratio: “number of positive intervals / total number of intervals”
(Duhamel et al. 2000; Quéré et al. 2000; Raoul et al. 2001). The observation of A. terrestris/
T. europaea indices was conducted during periods when vegetation was at its shortest.
SURVEY OF A. TERRESTRIS AND T. EUROPAEA POPULATIONS AND FARMING
PRACTICES
Relative abundance of A. terrestris population was observed during low density, increase and
high density phases of a population cycle.
Low density phase and increase phase
We selected communes that presented populations at low densities (score 0-1) for two years
after a high density phase (score 3). In these communes, 46 agricultural parcels (cadastral
units) in which A. terrestris and T. europaea were absent in spring 2001 were selected (size:
0.5 – 15 ha) in typical landscapes for the area of study (Delattre et al. 1996). Then, A.
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