Biological control of the ambermarked birch leafminer (Hymenoptera: Tenthredindae): monitoring establishment, spread, and native parasitism

The ambermarked birch leafminer (Profenusa thomsoni, Hymenoptera: Tenthredinidae) is an invasive sawfly native to Europe that has reached high densities in Alaska, where it invaded in the mid-1990s. In 2003, a cooperative biological control program with the United States Forest Service, the Canadian Forest Service and the University of Alberta was initiated against the leafminer. Lathrolestes thomsoni (Hymenoptera: Ichneumonidae) was identified as a biocontrol agent found in Edmonton Alberta where a similar invasion of the same leafminer had occurred in the early 1990s. There, Lathrolestes thomsoni caused the pest’s densities to decline by more than 90% and these have remained low since the pest population collapsed in early 2000. From 2004-2008, a total of 3636 Lathrolestes thomsoni wasps were released in Alaska. Using molecular techniques, we have shown that the wasp has established and spread. Two additional parasitoids have been found associated with the leafminer in Alaska: Lathrolestes soperi and Aptesis segnis. Lathrolestes soperi, a presumably native parasitoid, has been found parasitizing the leaf miner in the leaves. Over the 2006-2009 period, parasitism rates by L. soperi at permanent plots have increased significantly, suggesting that this parasitoid may also have an impact on the leafminer’s density. Aptesis segnis is believed, based on biology of congener species, to attack the leafminer in the soil. It has been recovered in large numbers in emergence cones placed under birch trees, which the leafminer overwinters.