Société nationale de protection de la nature et d'acclimatation de France, Paris (FRA)
Abstract
The spatial distribution of a larval population of wood- crickets (Nemobius sylvestris) has been studied into two obser vation quadrats, located close to the edges of an oak wood near Toulouse (fig. 1). In both study areas, population density varied seasonally, with peak numbers during summer and autumn, depending upon climatic conditions. Whereas larval distribution was clumped all the year round in quadrat A located near the E-W edge of the wood, the situation was different in quadrat B located near the NNe-SSw border of the same wood. The observed difference in larval distribution pattern between the two quadrats can be explained by the effect of forest border orientation upon the aggregation of wood-cricket larvae. At any time of the year, their numbers increased progressively, from the edge of the wood to 15 metres inside, in quadrat A. The situation was different in quadrat B, except in winter time. Larval distribution was also influenced by the proximity of trees. In quadrat A, the wood-cricket larvae were more numerous close to the base of the trees. This also occured in quadrat B, but only during the summer and the autumn. The various factors influencing the spatial distribution of Nemobius sylvestris larvae can act synergically or antagonistically, according to local conditions. However the proximity of a forest border and its orientation appear to play the major roles
