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

CHANGES IN THE FAUNA THROUGH MAN MADE ACTIVITIES

The region in precolonial times was almost entirely covered with dense mainly coniferous forests except in the driest valleys encountered in the south of the ecozone. Though, still largely forested, the Montane Cordillera Ecozone has been partly deforested and in open valleys with rich loamy soils, agriculture has expanded. Prairie habitats are probably the most threatened as it occupies a small portion of the ecozone and as very little of it has been left untouched. However, large tracts of many original habitats of the ecozone are still there and a wide range is under provincial and federal protection.

Except for Pristiphora erichsonii (Hartig) (larvae feed on larches), P. rufipes Lepeletier (larvae feed on currants and gooseberries) and Cephus cinctus Norton (feeds on wheat, oats and rye), other recorded Eurasian species are known from less than three or four localities. It seems that the introduced species play a minor role in the ecozone. This is in stark contrast with the situation in the Mixed Wood Plain Ecozone of southern Ontario and Quebec where they dominate (Goulet, 1996b).

Of the thirteen species recorded, two occur in wild places, Pristiphora erichsonii (larvae feed on larches) and Eriocampa ovata (Linnaeus) (larvae feed on alders), and the remaining nine are associated with man made habitats in agricultural settings or residencial areas.

Though, man’s presence is obvious in the southern third of the ecozone, the faunal composition has not been altered markedly even in lowland areas, it is still quite easy to find remnants of original habitats (though they may not be pristine). Deforestation especially followed by loss of soil is of concern as such land will not return to high quality forest or simply remained as open rock and bush land. Because forestry practices cover large areas of the ecozone, it is imperative that all efforts are done to insure sustainability not only of forest cover, but of the general biodiversity associated with these habitats. Sawflies are hardly associated with prairies and subdesertic habitats. However, such habitats are threatened because it is uncommon and is usually found in valleys. Such places are mainly used by ranchers. With the relatively high density of cattle restricted to enclosed areas, these large and heavy animals work the soil with their hoofs allowing establishment of alien weeds. So the ecosystem is obviously changed in its flora. These changes affect directly herbivorous insects depending on native plants that are becoming scarcer year after year.

Because of the rarity of most introduced species in the ecozone, there are probably little effects on native species. It is possible that the real picture is different since we have almost no recent sampling data from agricultural regions, and not least, a complete season sampling. I know that I am reporting on fragmentary evidences which are often from the 1950's. However, my brief incursions in the ecozone at low elevations do not support evidences for native species displaced by alien sawflies.

Table 5. List of larval host plants associated with introduced species. The plants are grouped into those associated with the ornamental trades, agricultural activities, and pastures and old field sites.

Plant genera (number of sawflies species per host plants)

I. Ornamental plants (generally introduced through nurseries)

Alnus (1) Prunus (1)

Larix (1) Pyrus (1)

Malus (1) Ribes (1)

Rosa (2) Sorbus (1)

Viola (1)

II. Pastures and old fields (probably introduced through boat ballasts)

Chenopodium (2) mosses (1)

Cirsium (1) Polygonum (2)

Juncus (1) Rumex (2)

III. Agriculture practice (probably introduced with hay for animal bedding)

Triticum(1) Hordeum (1)

Avena (1)

Lindroth (1954, 1957) discussed the origin of introduced insects into North America. He postulated that an important method for accidental introductions was by soil ballasts in boats coming from Europe. Ballasts consisted of soil shovelled in barrels from French and British ports. Grounds beetles found at these sites confirm Lindroth's hypothesis since almost every species from these drained, open, and damaged port sites are established in Canada. However, looking at the introduced species list of sawflies for our region and their associated larval host(s), other methods played significant roles. Species associated with meadow habitats and probably brought in with ballasts, account only for seven species (55%), those with ornamental plants (including fruit crops) account for five species (38%), and those with animal bedding account for only one species (7%) of Cephidae. Though many of the ornamental plants are forest or agricultural crops, the introduced species were almost entirely coming from imported nursery stocks of new or unusual varieties. Ornamental plants were commonly imported with soil root balls in this country from the early 1950's till the mid 1960's. Most likely numerous introductions came from these root balls. Root balls (i.e., with soil or moist peat moss around the root) of plants in their dormant state are ideal habitats for sawfly prepupae in their cocoon for transportation in the dormant state to Canada. Upon hatching these sawflies would find an abundance of their favourite food plant at the nurseries. Nurseries in large cities offer the largest selection of new varieties which are most in demand. Because most introduced insects through nurseries turned out to be economically significant to ornamental and forest crops, something needs to be done to stop the flow of introductions to North America.

Many of the introduced species show a marked disjunct distribution. Basically there is a large focus in northeastern North America centred around major Atlantic ports and Toronto, and another focus around Seattle and Vancouver. It is not clear if the western centre reflects an independent introduction or if they were imported trough trade from eastern North America. None of the recorded species in the Ecozone are found only in the western centre. However, along the Pacific coast there are species not recorded from eastern North America.

The introduction rate for sawflies is probably worse in this century than ever before. If we look at the beetles of Canada and Alaska (Bousquet, 1991), the only order with the needed information, introduced species make up 6% of the fauna of Canada. In sawflies, this rate is about the same in the ecozone. This is markedly different from the proportion of alien species recorded in the Mixed Wood Plain Ecozone (Goulet, 1996b). Also the influence of the alien fauna appears as much less significant as that found in the Mixed Wood Plain Ecozone.

In summary, the introduced fauna of sawflies is not very significant in the ecozone not only in terms of species, but in number of observations or collections.