Predator/prey ratios: A measure of bark-beetle population status influenced by stand composition in different French stands after the 1999 storms

Abstract

This study presents the results of a four-year trapping experiment in stands heavily infested by Ips typographus following the 1999 storms in north-eastern France. Ten bottle-traps were stapled on dead spruces or on broad-leaves in five spruce stands, among which two comprised pines, a species particularly favourable for the pupation of the predator, Thanasimus formicarius. The phenology of T. formicarius closely reflected that of its prey in all stands. We show that the proportion of pines within a 500 m radius is the main variable influencing predator/prey ratios, and that this variable alone outperforms other forest composition indices such as the Shannon diversity index estimated using all tree categories, or reduced to integrate only three categories (spruce, pine, others). These results are discussed with regard to the possible role of host trees and host-tree diversity in both insects' life-cycles and how the T. formicarius/Ips typographus ratios could be used to describe the status of Ips typographus infestations. © INRA, EDP Sciences, 2006.