The population dynamics of Sirex noctilio F.: diapause, dispersal and biological control.

The most significant ecological feature of invasive populations of the woodwasp Sirex noctilio, is the occurrence of pulse-like eruptive population outbreaks. These outbreaks are rapid, local increases in density and are usually terminated by natural enemies or resource defenses or depletion. While S. noctilio populations may remain at low, endemic levels for lengthy periods killing stressed tree specimens, during outbreaks, more generalized damage can be of great economic significance. The associated increase in wasp numbers occurring during outbreak phases, can also favor geographical spread. We present here an overview of recent ecological and behavioral studies of S. noctilio carried out in Patagonia (Argentina). We discuss the significance of these observations to our understanding of the observed patterns of wasp population dynamics and spread. We also discuss how these features may influence or are influenced by the introduction of natural enemies, during the implementation of biological control programmes.