Life historytraits of Sirex Noctilio F. (Hymenoptera: Siricidae) canexplain outbreaks independently of environmental factors

The woodwasp Sirex noctilio is a major pestof pine plantations worldwide. Economically significant damage ishowever limited to outbreak populations. To understand whatdetermines outbreaks dynamics in this species, we developed anindividual based model for a wasp population developing within apine plantation. We show that outbreaks may be the result of theinsect's life history. Specifically we show that limited dispersalmay not only increase population persistence but also create theconditions for eruptive dynamics. When the probability of longdistance dispersal is greater than zero, but relatively small($P_{LDD}$= 0.1) large outbreaks are the norm, with all of thesuitable trees dead at the end of the simulation. For $P_{LDD}$= 0(only local dispersal allowed) outbreaks are smaller in size, andin some cases not well defined and spread over longer periods. For$P_{LDD}$= 1 (only long distance dispersal allowed), the frequencyof local population extinction (without outbreaks) increasessignificantly. Aggregated attacks may induce physiological changesin the trees which could allow other wasps to detect them. Thesechanges may in turn trigger an outbreak. In contrast, healthy,vigorous trees are not suitable for wasp oviposition. In our modelthe density of suitable trees (healthy trees but yet suitable foroviposition) are a key factor determining population persistencebefore outbreaks. From an applied perspective, our resultsemphasize the importance of adequate plantation management inpreventing woodwasp infestation.