Phenology and life history of the invasive Adelges piceae in the intermountain west

Adelges piceae (Ratzeburg), commonly called the balsam woolly adelgid, is a forest insect likely native to the Caucasus Mountains of Europe that has expanded into the Intermountain region of North America. This pest attacks true firs (Abies spp.), where it restricts water flow, causes crown dieback, and accelerates tree mortality. The abundant high elevation subalpine fir, Abies lasiocarpa (Hook.) Nutt., has exhibited a high degree of susceptibility to A. piceae. Current understanding of A. piceae phenology, life history, and host plant susceptibility and mortality is limited in its non-native ranges and is a critical need to support development of effective management strategies. In this preliminary study, bark samples of A. lasiocarpa infested with A. piceae were collected from 6 sites in northern Utah from August to November, 2020, and February to November, 2021. Site characteristics of air and soil temperature, slope, and elevation (ranging between 1,900 and 2,400 meters) as well as sample tree DBH and gouting presence/severity were collected. A. piceae life stages (egg, three nymphal instars, and adult) were enumerated and assessed in relation to temperature and precipitation patterns to support development of a life history and degree-day phenology model. Results from observing A. piceae phenological and life history patterns in sites of differing characteristics will allow for the implementation of timely and efficient management practices for infested A. lasiocarpa trees based on stand microclimate and elevation.