|VAN DRIESCHE, ROY - University Of Massachusetts, Amherst|
|OSNAS, JEANNE - University Of Alaska|
Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/2023
Publication Date: 6/25/2023
Citation: Van Driesche, R.G., Duan, J.J., Osnas, J. 2023. Effect of tenthredinid leaf miner invasions on growth of Alaska white birch in Anchorage, Alaska, and the interaction with biocontrol of ambermarked birch leaf miner. Florida Entomologist. 106(2):110-116. https://doi.org/10.1653/024.106.0207.
Interpretive Summary: The invasive ambermarked birch leaf miner formerly caused severe damage to birch trees in southeastern Alaska until the successful introduction of a parasitic wasp significantly reduced the level of damage. We analyzed historical birch growth rates since the leaf miner’s invasion and successful biological control. During the 11-year period following the successful biocontrol of this leaf miner, growth of white birch did not recover to pre-outbreak levels, but instead declined further. This lack of recovery may be the result of a more recent invasion in 2008 of a second species of birch leaf miner.
Technical Abstract: Ambermarked birch leaf miner, Profenusa thomsoni (Konow) (Hymenoptera: Tenthredinidae) (AMBLM), invaded the Anchorage region in southeastern Alaska circa 1991 and by 1996 caused high levels of mining, resulting in browned foliage each year by late summer. A biological control program was begun in 2004 based on the importation of the larval parasitoid Lathrolestes thomsoni Reshchikov (Hymenoptera: Ichneumonidae), which suppressed an outbreak of AMBLM previously in Alberta. By 2008, this introduced parasitoid (and two previously present species) reduced damage to Alaska white birch by >50%. In 2020, as a follow up, 100 Alaska white birch in forested parks in Anchorage were cored to see if leaf mining had previously reduced tree growth during the outbreak and whether biocontrol of AMBLM allowed tree growth to recover. Compared to 12 years (1984-1995) before the start of the outbreak, radial growth was suppressed by ca 25% during the outbreak (1996-2007). During the 11-years after suppression of damage through biocontrol (2008-2018), tree radial growth of Alaska white birch did not recover, but rather declined further. This pattern may be due to the invasion circa 2008 of another birch leafminer, Heterarthrus nemoratus (Fallén) (Hymenoptera: Tenthredinidae). A survey in 2021 found 90% of all mining in Anchorage was from the second leaf miner, which had a near zero level of larval parasitism, compared to 60% in the few AMBLM collected. Alternatively, some studies of defoliation at high latitudes suggest that birch trees may continue to show suppressed growth long after actual pest damage ends.