Henri Goulet. 1998. Sawflies (Hymenoptera: Symphyta) in Smith, I.M., and G.G.E. Scudder, eds. Assessment of species diversity in the Montane Cordillera Ecozone. Burlington: Ecological Monitoring and Assessment Network, 1998.

SAWFLIES
(HYMENOPTERA: SYMPHYTA)

Henri Goulet

CURRENT DIVERSITY OF SAWFLIES

Table 1. Number of species recorded, known and expected species, and main type of distribution of these species for each family and subfamilies in the Montane Cordillera Ecozone, and the total diversity of Symphyta for the area.

The first two columns of Table 1 summarize the diversity of species recorded for each family and subfamily. Among the Symphyta, 254 species have been recorded and 40 more are expected mainly from the Pacific coast region, and the northern regions of Montana, Idaho and Washington. So we have a total of 294 species recorded in or expected in the ecozone. The fauna for this region is not that well known as 14% of the species await discovery.

The above diversity table includes 11 families and 69 genera. Only the species of four genera, Pontania, Phyllocolpa, Nematus and Euura, have been omitted due to the unresolved taxonomy in our region. However, there are species in each of these excluded genera that are recorded in the Montane Cordillera Ecozone.The fauna is moderately diverse if one compares it with 119 genera in Canada and 144 genera for all of North America north of Mexico. Eleven genera are expected to be discovered in the region (see Appendix A). The largest family is the Tenthredinidae with 200 known species. This is followed by the Pamphiliidae (14 species), the Siricidae (9 species), the Argidae (9 species) and the Xyelidae (8 species). All remaining families, Diprionidae, Cimbicidae, Cephidae, Siricidae, Xiphydriidae and Orussidae, have at most five known or expected species.

There is an average of 3.7 species per genus. In the ecozone, 56% of the genera have only one species, 87% have less than five species, and only 12% have more than five species. The most diverse genus is Tenthredo with 30% of the species (76 species). Tenthredo and the four most diverse genera (Dolerus with 23, Pristiphora with 17, and Amauronematus with eight comprise 50% (124 species) of the total known diversity in the ecozone.

The last three columns of Table 1 summarize the general distribution pattern of species found in our region. Out of 254 species, 13 (5%) are introduced into North America from Eurasia (Alien), 36 (14%) are indigenous to Eurasia and North America (Holarctic), and 205 (81%) are indigenous to North America (Nearctic). For the region under study, the Nearctic species are predominant, and a sizable number of Holarctic species with mainly boreal ranges which extend in the northern half of the ecozone and along the eastern cordillera. The proportion of accidentally introduced species of sawflies is slightly less than that of beetles (6%) (Bousquet, 1991), but markedly less than that of vascular plants (28%) (Scoggan, 1978). Introduced vascular plants are due to accidental and deliberate introductions of desired plants, but the alien sawflies are probably due entirely to accidental introductions.

Because there are so few introduced species, the differences seen between families and subfamilies are not marked. The small proportion of introduced species is probably due to mountain barriers along the western border of the ecozone in relation to major ports along the Pacific coast and to vast dry regions to the south of British Columbia. The ecozone is most likely not the area of introduction. I assume that each species filtered into the ecozone from coastal regions where they are known to occur. Species with Holarctic ranges are quite common in this ecozone because the ecozone is rather near the beringian refugium which has the greatest diversity of Holarctic species in North America. Moreover, there are numerous north/south avenues from the Yukon Territory into the Montane Cordillera Ecozone. However, 33% of the species of Nematinae show such wide range. The species of Nematinae (Tenthredinidae) which are more diverse in boreal regions are very rich in Holarctic species. The dominance of species with Nearctic range over those with Holarctic ranges (60 - 100%) is seen in all families and subfamilies.