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 RANGES AND POPULATION LEVELS

Sawflies are less well sampled than ground beetles and many groups of moths because of much fewer amateursand professional collecting them. Therefore, the diversity is incompletely known and the ranges are very roughly outlined. Based on my limited field work and that of my predecessors in the ecozone, I have not discovered any recent drops in populations or change in distribution of native species.

Drop in abundance

However, one introduced forest pest has become most uncommon in the past 10 to 15 years in our region, the larch sawfly (Pristiphora ericksonii (Hartig)). The population of P. erichsonii was brought under control by Olesicampe benefactor Hinz in the 1960's (Ives and Muldrew, 1984). A remarkable drop in all species of the genus Tenthredo was observed in Eastern Canada, but there is not the slightest evidence of any drop in any population of species of this genus or any other in the ecozone. Not only, the genus Tenthredo is the most diverse among Symphyta in the ecozone, but it is also the most commonly collected type of sawfly in most habitats except in open prairie and semidesert habitats. By any sampling techniques, one may expect that specimens of Tenthredo may represent between 50 and 90% of all Symphyta collected as compared to about 1% in agricultural regions of the Mixed Wood Plain Ecozone (Goulet, 1996b). The limited amount of agricultural land, and the limited use of herbicides and insecticides in most ecoregions may explain the predominance of Tenthredo specimens.

The biology of Tenthredo species is unusual for sawflies. Based mostly on European host data, larvae feed over an extremely wide range of plants, from ferns to Asteraceae and Fabaceae. Generally, most species are recorded from one host species. The most common types of host plants are herbaceous. Moreover, adults are exceptional among sawflies as they are predators and usually pollinators (Goulet, 1996a). The predatory behaviour is marked and similar to that of tiger beetles. Adults of many species actively pollinate many plant species and feed on nectar. Adults of oviposit generally later than most tenthredinid sawflies in June to late August. Finally, adults are large and remarkably showy Hymenoptera, and thus, have been regularly collected by entomologists.

Increase in abundance and ranges

The present data is too limited to show increases in ranges for any native and introduced species. There is no doubt that the few introduced species are in the process of expanding generally in man made habitats.

In conclusion, the general trends of population changes are that most native species probably have maintained normal population levels, and that the few introduced species may be spreading.