University of Alberta Museums Search

Adults: Females only, males not recorded. Small black sawflies approx. 4 mm long. Middle tibia whitish, all tarsi black to whitish but variable. Can be distinguished from Fenusa pumila by length of antennae; are longer than thorax in F. dohrnii (shorter than thorax in F pumila). All sawflies of this group posses an ovipositor modified to be used as a saw to facilitate the deposition of eggs under the surface of leaves. Serrula (teeth) of lancet (saw) low and flat but more obvious than those on the saw of F. pumila. Larvae: Creamy white with a black band on the ventral surface of the thorax, more visible in the later feeding stages. The body is covered in small dark spines and with fewer teeth on the mandibles than Fenusa ulmi or F. pumila. There are 6 instars. The three North American Fenusa species complete development inside leaves of the host plant. Therefore, the larval host is an important diagnostic character. Fenusa dohrnii feeds in Alder, F. pumila on Birch and F. ulmi occurs in eastern North America on Elm. Adapted from Smith 1971.

Generally similar to other members of the tribe. Only available description of the life history from Slingerland 1905 (as cited in Smith 1971). Species is believed to be parthenogenic. Females oviposit in the leaf surface in the centre part of newly expanded or expanding Alder leaves (Frankenhuyzen van 1970). Larvae feed for approximately 3 weeks before dropping to the ground to pupate. Based on larval activity still being evident in September there are likely multiple generations per year (Smith 1971). Digweed & Langor (2004) observed active larvae in late August and early September in the Northwest Territories, south of the 64th parallel indicating a similar life history in Canada.

Larvae feed in Alder (Alnus), a member of the Betulaceae, from a number of species; Speckled Alder (A. incana subsp rugosa), Mountain Alder (A. incana subsp. tenuifolia), European Alder (A. glutinosa) and A. rugosa (serrulata). From records in Digweed & Langor 2004 and Smith 1971.