SAWFLIES (Hymenoptera: Symphyta)
Henri Goulet
CHANGES IN THE FAUNA THROUGH MAN MADE ACTIVITIES
The Ecozone before colonial times was almost entirely covered with dense forests except
for open drained habitats such as land slides near rivers and lakes, alvars and remnant
prairies. Remnant prairies were maintained or enlarged by native people burning the land. Thus, the
fauna of open habitats was very restricted and insular in nature
with probably less diverse fauna than expected. Today most of the Ecozone consists
of open agricultural pastures and crop fields. Such habitats extend almost uninterrupted from northern
United States to the prairie region.
For this discussion, I include both native species and introduced species of the Ecozone.
Table 4. Number of native and introduced species with known larval host(s) either occurring in, or restricted to: man-made habitats; both native and man-made habitats; or mainly restricted to native habitats. Codes: ( ) = native, [ ] = introduced
| Taxon Name | Number of Species | |||||||
| Family Subfamily | Man-made habitats | In both native & man-made habitats | Native habitats | Total | ||||
| Argidae | (1) | [1] | (2) | [0] | (17) | [0] | (20) | [1] |
| Cephidae | (0) | [0] | (2) | [2] | (3) | [0] | (5) | [2] |
| Cimbicidae | (0) | [0] | (1) | [1] | (6) | [0] | (7) | [1] |
| Diprionidae | (0) | [0] | (3) | [3] | (13) | [0] | (16) | [3] |
| Orussidae | (0) | [0] | (0) | [0] | (2) | [0] | (2) | [0] |
| Pamphiliidae | (0) | [0] | (2) | [1] | (30) | [0] | (32) | [1] |
| Pergidae | (0) | [0] | (0) | [0] | (3) | [0] | (3) | [0] |
| Siricidae | (0) | [0] | (0) | [0] | (9) | [0] | (9) | [0] |
| Tenthredinidae | ||||||||
| Allantinae | (0) | [6] | (15) | [1] | (10) | [1] | (25) | [8] |
| Blennocampinae | (0) | [3] | (4) | [2] | (16) | [0] | (20) | [5] |
| Heterarthrinae | (0) | [2] | (3) | [7] | (9) | [2] | (22) | [11] |
| Nematinae | (0) | [7] | (4) | [11] | (50) | [0] | (54) | [18] |
| Selandriinae | (0) | [2] | (10) | [0] | (8) | [2] | (18) | [4] |
| Tenthredininae | (0) | [1] | (1) | [0] | (11) | [0] | (12) | [1] |
| Xiphydriidae | (0) | [0] | (0) | [0] | (6) | [1] | (6) | [1] |
| Xyelidae | (0) | [0] | (0) | [0] | (9) | [0] | (9) | [0] |
| Total | (1) | [22] | (47) | [28] | (205) | [6] | (250) | [56] |
Few of the native species in Table 4 are restricted to man-made habitats, though at least 19% of the species from native habitats occur also in man-made habitats on plants introduced for cultivation.
In the Allantinae and Selandriinae an unusual proportion of species (60% and 55% respectively) live in man-made habitats as their host plants also occur there. The opposite is true for the Tenthredininae which are rarely found in man-made habitats (the proportion is actually much lower than shown in the table above since we know very little about their host plants).
With introduced species the habitat selection is opposite. Indeed, 89% of the introduced species are living in man-made habitats (see Table 4). This is basically the opposite of native species habitat preferences (Table 8) and 39% are restricted to them. Only 6% of the introduced species occur in native habitats. These insects are usually feeding on introduced plants, and many are significant economically on agricultural crops and ornamental plants.
Most of the species (60%) in man-made habitats are Tenthredinidae especially the three subfamilies, Allantinae, Heterarthrinae and Nematinae. These subfamilies include most of our agricultural pests.
The impact of man's activities on the fauna of the Ecozone is profound. Fifty-six species have been introduced. These species dominate man-made habitats. The native fauna withdraws to the remnants of natural habitats. These natural habitats are not generally pristine but are also affected by the invading alien flora and fauna. So we are not able to extrapolate about the effect of man on the native fauna because the most important sawfly collections are less than 100 years and the effect of the aliens on our original fauna goes back to hundreds of years.
I know of few examples of recent introductions affecting native species. The impact has been either a marked reduction in a native species populations (e.g. Dolerus nitens Zaddach introduced on the 1960's almost replaced the very common D. unicolor in the 1970's) or an apparent complete elimination of the native species (e.g. I do not know of an example among sawflies, but in beetles, the elimination in the 1980's of Coccinella transversoguttata Fald. over most if not all of the MWPE by C. septempuncttata Palliardi, first found in 1978, is very impressive).
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 species recorded for host plants)
I. Ornamental plants (generally introduced through nurseries)
| Acer | (1) | Pinus | (3) |
| Alnus | (6) | Populus | (2) |
| Aquilegia | (1) | Prunus | (2) |
| Betula | (9) | Pyrus | (3) |
| Crataegus | (1) | Quercus | (1) |
| Ferns | (1) | Ribes | (1) |
| Larix | (1) | Rosa | (6) |
| Ligustrum | (1) | Rubus | (4) |
| Lonicera | (1) | Salix | (3) |
| Malus | (1) | Sorbus | (2) |
| Osmunda | (1) | Ulmus | (1) |
| Picea | (1) | Viola | (1) |
II. Pastures and old fields (probably introduced through boat ballasts)
| Chenopodium | (2) | Lactuca | (1) |
| Cirsium | (1) | mosses | (1) |
| Fragaria | (2) | Potentilla | (1) |
| Galium | (1) | Polygonum | (2) |
| Juncus | (1) | Ranunculus | (3) |
| Grasses | (2) | Rumex | (2) |
III. Agriculture practice (probably introduced with hay for animal bedding)
| Triticum | (2) | Hordeum | (2) |
| Avena | (2) |
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 list of introduced species list of sawflies for our region and their associated larval host(s), another method played a more significant role. Species associated with meadow habitats and assumed brought in with ballasts, account only for 11 species (20%), those with ornamental plants (including fruit crops) account for 43 species (76%), and those with animal bedding account for only 2 species (4%) 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 until the mid 1960's. Undoubtedly, 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 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 are economically significant to ornamental and forest crops, something needs to be done to stop the flow of introductions to North America.
With today's technology of meristem duplication, there should be no reason to import unusual or new strains. New varieties should be simply duplicated in North America. Such an approach would markedly reduce the introduction rate of insects into North America.
The introduction rate for sawflies and probably several other herbivorous insects 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. In sawflies, this rate is almost twice as high. Similar rates are seen in the Curculionidae, a plant feeding group (Bousquet, 1991). Such rates no doubt have a profound impact on our economy and our native fauna.
I feel that most of our original fauna is still present as we still have most habitats frequented by sawflies. Most known species for our region were rediscovered in the past 20 years. However, in number of specimens per species based on collecting and the ever increasing acreage of man-made habitats, our fauna shows a very dramatic change. In summary, the introduced fauna of sawflies is clearly dominant today in terms of specimens in most of the MWPE, and will get even more dominant as introduced species expand their range and additional species become established unless some quarantine rules become more strictly enforced.