Associations Among Serropalpus substriatus (Coleoptera: Melandryidae) and Sirex (Hymenoptera: Siricidae) Communities

Serropalpus substriatus Haldeman (Coleoptera: Melandryidae) develops within the same trees as Sirex noctilio F. and Sirex cyaneus F. (Hymenoptera: Siricidae). This species is now reported emerging from red pine (Pinus resinosa Sol. ex Aiton) and balsam fir (Abies balsamea (L.) Mill.) (Pinaceae) in eastern North America. Numbers of Se. substriatus emerging from pines were always much lower than numbers of Sirex in trees, and 18% of Se. substriatus required 2 years before emergence. During first years of emergence, Se. substriatus was found in only 12 of 41 sampled red pines infested by Si. noctilio. Trees from which Se. substriatus emerged hosted higher densities of Sirex than trees without Se. substriatus. Comparing dually infested trees, Deladenus siricidicola Bedding, the parasitic/mycophagous nematode associated with Si. noctilio, was found parasitizing one of 141 (0.7%) Se. substriatus. This is the first report of a non-target impact of D. siricidicola in North America, but parasitism was very low in this uncommonly encountered woodboring beetle. In Europe, a related species, Serropalpus barbatus Schaller, has also been reported to be parasitized by D. siricidicola.