Successful Biological Control Of The Ambermarked Birch Leafminer, Profenusa Thomsoni (Hymenoptera: Tenthredinidae), In Anchorage, Alaska: Status 15 Years After Release Of Lathrolestes Thomsoni (Hymenoptera: Ichneumonidae)

In Anchorage, Alaska, larvae of the invasive ambermarked birch leafminer (AMBLM), Profenusa thomsoni Konow (Hymenoptera: Tenthredinidae), are parasitized in leafmines by Lathrolestes thomsoni Reshchikov and L. soperi Reshchikov (Hymenoptera: Ichneumonidae). The first species was introduced to Alaska from Alberta and the Northwest Territories of Canada beginning in 2004 after it was noted to be associated with the collapse of an outbreak of AMBLM in Alberta. The second species, L. soperi, was described in 2010 after it was found attacking AMBLM larvae in mines in Anchorage. In previous studies, we documented that after the release of L. thomsoni in Anchorage, AMBLM densities declined from 70% leaves mined in 2006, to 19% in 2011, and that parasitism of AMBLM larvae in mines by the two Lathrolestes species combined rose from 8% in 2006 to 32% in 2011. Here we conduct another post-release survey and find that the percentage of leaves mined has been reduced even further to 9%, and that parasitism rates by the Lathrolestes species have reached 70% in 2019. We then used DNA sequencing to determine the relative dominance of the two species of Lathrolestes by dissecting out individual parasitoid eggs or larvae from 249 parasitized AMBLM larvae collected in August 2019. In total, 207 parasitoid eggs or larvae were successfully sequenced and identified from 200 leafminer larvae, of which seven were supernumerary larvae in four host larvae. DNA sequencing indicated that of AMBLM larvae that were parasitized, 71% (n = 142) were parasitized by L. thomsoni, and 29% (n = 58) were parasitized by L. soperi. AMBLM now appears to be at non-pest densities at most sites in Anchorage, with the majority of biological control services provided by the introduced L. thomsoni.