Elm leafminer

The elm leafminer, Fenusa ulmi, has been in the Northwest for a few years but has been noticeable in its expansion to new areas in Washington and Oregon recently. The sawfly attacks Scotch and Camperdown elms, Ulmus glabra), Engish elm, U. procera; and American elm (Johnson and Lyon, 1991). Scannell reported no damage on American elm in her research (Scannell, 2000). Leaves can be so heavily mined that the trees defoliate. Most trees flush again and do fine. Camperdown elms often hold onto partially mined leaves which can be an aesthetic problem (Sharon Collman, pers. comm.).

According to research by Christine Scannell at the the University of Washington, the adult sawflies emerge coinciding with the breaking of the leaf buds of most elms, although after leaf expansion of American and European white elms (Scannell, 2000). The timing of emergence ranged from mid-March through mid-April depending on temperatures during the course of several years of study.

The sawflies tend to emerge during the middle of the day with maximum emergence occurring between11:00 am and 1 pm. The adults are all female and begin to lay eggs immediately after emergence. The eggs are usually laid near leaf veins initially but later oviposition is without regard to location of the veins (Scannell, 2000).

There are five instars of the larvae. In 2000, the larvae were found 10 days after the first emergence of the adult sawflies (Scannell, 2000). The larvae eventually drop to the ground where they are reported to pupate through the summer, fall, and winter. There is one generation per year (Johnson and Lyon, 1991).

Monitor for adults when sun is present on the foliage in order to better see them. First tiny mines are also a good indicator. 

Literature:

Johnson, W.T. and H.H. Lyon. 1991. Insects that Feed on Trees and Shrubs. 2nd. Ed. Cornell University Press. 560 pp.

Scannell, C.M. 2000. The Biology and Seasonal Life History of the Elm Leaf Miner, Fenusa ulmi (Sundevall), in the Pacific Northwest (Hymenoptera: Tenthredinidae). Master's Thesis, University of Washington.

 

Page last modified 4/20/16

Elm leafminer larva removed from mine. Photo: Rosetta

Elm leafminer larva removed from mine.
Photo: Rosetta

Elm leafminer silhouettes closeup. Note the leaf has been completely mined.

Elm leafminer silhouettes closeup. Note the leaf has been completely mined.
Photo: Rosetta

Elm leafminer damage closeup. Photo: Erik LaGasa, WSDA

Elm leafminer damage closeup.
Photo: Erik LaGasa, WSDA

Elm leafminer damage closeup. Photo: Erik LaGasa, WSDA

Elm leafminer damage closeup.
Photo: Erik LaGasa, WSDA