Dr. Neil Thompson is an Associate Professor of Forestry at the University of Maine Fort Kent.
Combined efficacy of the treatment program and the action of natural enemies has been very high in 2026. Immediate effects of tebufenozide applications were apparent in the days following application, continuing for ~2 weeks. Where a Btk block and Tebufenozide block were adjacent near a point with an L2 count of 43, there was no apparent difference between the products two weeks after the applications: both had 1-2 survivors per branch as is generally expected. Dr. Rahimzadeh-Bajgiran and her graduate students have flown remote sensing drones at four sites with Btk/tebufenozide intersections; this will take some time to process but no visible differences were noted on the ground.
Effects of natural enemies were likely enhanced by this year’s weather pattern: the cool, rainy period during the L4-L6 feeding window delayed maturation, with every day presenting more opportunities for parasitoids to find their hosts. Treatments early in the feeding season reduced the host availability within the blocks, increasing the rate of parasitism on survivors. A study led by Dr. Mech is in its first of three years investigating this phenomenon: larvae and pupae were sampled weekly at six sites, and their parasitoids are being reared out and identified.
Truly complementary/additive mortality is a cornerstone of EIS and has been particularly stark with the early timing of treatments in these past two years. Treatments have been initiated precisely with the availability of host foliage, and they have been completed quickly. As the effects of the treatment taper off, a wave of parasitism hits the remainder of the population, including within-block survivors, in buffers, and areas near the treatment blocks.
Surveys of the 2026 migration are nearly complete, and evaluation of the 2026-27 overwintering population is just beginning. Maine Forest Service aerial survey flights found no defoliation outside of known areas in the Fish River and St. John valleys. Six automated pheromone traps along the Maine/Quebec border tracked the timing of moth migration flights, and the Maine Forest Service pheromone trap network has tracked the distribution of moths within the state. High counts along the western border between Big 10 and Big 20, and in the Fish River/St. John valleys, suggest strong short-range migration from established populations. High counts at several traps downeast suggest successful long-range flights, in line with long-range migration model outputs. The overwintering population (L2) survey is starting with ~40 sites collected in the first week in the vicinity of pheromone traps with high catches.
Preliminary maps will be available in early September, and models will be refined as additional samples are processed through the end of 2026.