Population biology of the European woodwasp,Sirex noctilio, in Galicia, Spain

Abstract

AbstractSirex noctilioFabricius (Hymenoptera, Siricidae) is rare and rarely studied where it is native in Eurasia, but is a widespread pest of pines in the Southern Hemisphere. Here we report on the abundance, basic biology, host use patterns and natural enemies of nativeS. noctilioin Galicia, Spain. Most trees attacked byS. noctiliofailed to produce any adult progeny: >90% of emergences came from <20% of the attacked trees. The highest reproduction was inPinus pinaster, followed byPinus sylvestrisandPinus radiata.The proportions ofS. noctiliorequiring 1, 2 or 3 years for development were 0.72: 0.24: 0.04. Delayed development could be an adaptation to avoid parasitic nematodes, which sterilized 41.5% adults with one year generation time but only 19% of adults with 2 years generation time. Hymenoptera parasitoids accounted for 20% mortality. Sex ratios were male biased at 1: 2.9. Body size and fecundity were highly variable and lower than previously reported from the Southern Hemisphere. On attacked trees, there were 5–20 attacks per standard log (18 dm2), with usually 1–3 drills per attack. Attack densities and drills per attack were higher in trees that subsequently died. The production ofS. noctilioper log was positively related to total attacks, and negatively related to: (1) attack density, (2) incidence of blue stain fromOphiostomafungi and (3) frequency of lesions in plant tissue around points of attack. A preliminary life table for S.noctilioin Galicia estimated effects on potential population growth rate from (in decreasing order of importance) host suitability, unequal sex ratio, parasitic nematodes and Hymenoptera parasitoids.