Predation of larval siricid woodwasps (Hymenoptera: Siricidae) by woodpeckers in Europe.
Predation of siricid larvae in coniferous trees by woodpeckers was studied at 10 sites in Belgium, German Federal Republic, Corsica and Switzerland. Siricid-infested logs with evidence of woodpecker excavations were dissected to determine total siricid populations and numbers of larvae preyed upon. Of the logs collected, 17% had been worked by woodpeckers (probably Dryocopus martius and Picoides major). Tree species worked by woodpeckers included Picea abies, Abies alba, Pinus nigra and P. sylvestris. Species of siricids preyed upon included Sirex noctilio, S. juvencus, S. cyaneus, Urocerus gigas and Xeris spectrum. Overall predation was 28.8% of a total population of 3617 larvae in logs worked by woodpeckers. Based on the total siricids available in all timber collected, predation was 6.1%. The relationship between larval populations per woodpecker-worked log and predation showed that percentage prey collection was greatest when prey populations per log were low and that this rate decreased as prey population per log increased. However, there was a positive linear relationship between numbers of larvae taken and the total population of siricids per log.