CURRENT DIVERSITY OF SAWFLIES

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

TAXON NAME Family    Subfamily	KNOWN	EXPECTED TOTAL	NO. OF NEARCTIC SP.	NO. OF HOLARCTIC SP.	FOREIGN
Argidae	21	23	22	0	1
Cephidae	7	7	5	0	2
Cimbicidae	8	8	7	0	1
Diprionidae	19	19	19	0	3
Orussidae	4	4	4	0	0
Pamphiliidae	43	46	44	1	1
Pergidae	3	3	3	0	0
Siricidae	9	9	2	7	0
Tenthredinidae
Allantinae	42	46	37	1	8
Blennocampinae	33	35	28	2	5
Heterarthrinae	23	23	13	0	10
Nematinae	78	88	64	6	18
Selandriinae	52	55	45	6	4
Tenthredininae	93	88	94	3	1
Xiphydriidae	6	10	9	0	1
Xyelidae	9	9	7	2	0
TOTAL	450	483	400	28	55

The first two columns of Table 1 summarize the diversity of species recorded for each family and subfamily. Among the symphyta, 450 species have been recorded and 33 more are expected since they occur in Michigan, northern Ohio and northern New York. So we have a total of 483 species recorded in or expected from the Ecozone. The diversity for the Ecozone is rather well known since only 7% of the species are expected but not yet collected.

Table 1 table includes 11 families, 23 subfamilies and 105 genera. Only the species of 3 genera, Pontania, Phyllocolpa and Euura, have been omitted due to the unresolved taxonomy in the region. However, there are species in each of these excluded genera that are recorded from the MWPE. Thus, there are 108 genera. This is an exceptional diversity if one considers that there are 119 genera in Canada and 144 genera for all of North America north of Mexico.

The largest family is the Tenthredinidae with 345 known and expected species. This is followed by the Pamphiliidae (43 species), the Argidae (21 species) and the Diprionidae (19 species). All remaining families, Xyelidae, Pergidae, Cimbicidae, Cephidae, Siricidae, Xiphydriidae and Orussidae, have at most 10 known and expected species.

There is an average of 4.6 species per genus. In the MWPE, 40% of the genera have only one species, 75% have less than 5 species, and only 11% have more than 9 species. The most diverse genus is Tenthredo with 53 species (11% of the symphyta fauna). Tenthredo and the ten most diverse genera (Dolerus with 41, Macrophya with 34, Nematus with 21, Pristiphora with 17, Arge with 16, Acantholyda and Pamphilius each with 14, Neodiprion with 13 and Hoplocampa and Ametastegia each with 10) comprise 50% (241 species) of the total known and expected diversity in the Ecozone.

The last three columns of Table 1 summarize the general distribution pattern of species found in the Mixedwood Plains Ecozone. Out of 483 species, 55 (11%) are introduced into North America from Eurasia (Foreign), 28 (6%) are indigenous to Eurasia and North America (Holarctic), and 400 (83%) are indigenous to North America (Nearctic). For the region under study, the Nearctic species are predominant, and typically few Holarctic species with mainly boreal ranges extend into the northern fringes of temperate regions. The proportion of accidentally introduced species of sawflies (11%) is greater than that of beetles (6%) (Bousquet, 1991), but much less than that of vascular plants (28%) (Scoggan, 1978). The very high proportion of introduced vascular plants is due to accidental and deliberate introductions of desired plants, but that of sawflies is probably due entirely to accidental introductions.

In some families or subfamilies there is an unusually low proportion of introduced species (e.g. introduced species represent 1% of the Tenthredininae, and 2% of the Pamphiliidae). In other subfamilies of the Tenthredinidae, introduced species are exceptionally numerous (e.g. introduced species represent 44% of the Heterarthrinae, and 20% of the Nematinae). The Heterarthrinae are most unusual in that we now have 50% of all known British species in the MWPE. Species with Holarctic ranges are uncommon in our area. However, 77% of the Siricidae show such wide range. The Nematinae (Tenthredinidae) which are more diverse in boreal regions are very rich in Holarctic species, but only few species extend into our area. The greater diversity of Siricidae with Holarctic range may be due to the very powerful flight of these insects, and to the diversity and the extensive ranges of their hosts plants. The dominance of species with Nearctic range over those with Holarctic ranges (90 - 100%) is seen in all families and subfamilies except in the Siricidae.

In appendix A is a list of species of the Selandriinae, a subfamily of the Tenthredinidae. This subfamily is statistically representative of the suborder, represents about 10% of all recorded species, has excellent distribution data, and its ecological requirements are well known. Most or 93% of species of Selandriinae are resident, and only 7% are introduced. Almost all species (94%) are recorded from Ontario, and about 75% are recorded from Quebec.
The four ecoregions differ slightly. There are more species (89%) recorded from the St. Lawrence lowlands Ecoregion than along the Erie Lowland Ecoregion (63%). These differences are in line with my general observations that sawflies are more diverse in cold temperate areas than in the warm temperate areas of eastern North America. The other two Ecoregions are not as well sampled; we have only limited data from the Frontenac axis Ecoregion (the specimens are still being prepared), and sampling has been less intensive in the Manitoulin-Lake Simcoe Ecoregion. However, both Ecoregions should offer a diversity similar to the St. Lawrence lowlands. I found no example of southern species isolated in the Frontenac axis. In the Frontenac axis, there is a marked increase in abundance of specimens and species of the genus Macrophya, a genus of Tenthredininae which is more diverse in the warm temperate areas of eastern North America. All species recorded have been found as far north as Ottawa.

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