Population Dynamics of Sirex noctilio: Influence of Diapause, Spatial Aggregation and Flight Potential on Outbreaks and Spread

Abstract

The most significant ecological feature of invasive populations of the wood boring wasp Sirex noctilio, is the occurrence of pulse-like eruptive population outbreaks.Pulse-like outbreaks are rapid, local increases in density and are usually terminated by natural enemies or resource defenses or depletion. S. noctilio populations may remain at low, endemic levels for lengthy periods killing stressed tree specimens, during outbreaks more generalized damage, through the attack of large numbers of healthy trees, 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 outline the patterns of adult emergence, where delayed adult emergence is noted and describe reported strong spatial aggregation and redistribution of S. noctilio attacks, within a pine plantation. We finally report on very recent work on the potential dispersal capacities of S. noctilio males and females. We discuss how these ecological features observed for S. noctilio populations in may influence or are influenced by the introduction of natural enemies, during the implementation of biological control programmes. Our emphasis throughout, is on adding-up recent research of wasp population ecology to prior information. Our general aim is to stimulate a critical understanding of the population ecology of S. noctilio, and consequently improve our abilities to manage established and expanding populations.