Date of Award:


Document Type:


Degree Name:

Master of Science (MS)



Committee Chair(s)

Diane G. Alston


Diane G. Alston


Barbara J. Bentz


Carol von Dohlen


Balsam woolly adelgid (BWA) is an invasive true fir pest in North America. Native to Europe, BWA was first discovered in Utah attacking subalpine fir in 2017. Recent BWA-caused subalpine fir mortality in northern Utah has prompted the need for baseline biological research to support pest management. Small-bodied and blending easily with its environment, BWA is a challenging pest to detect and study. Phenology, or the timing and characteristics of life stages through the year, of BWA varies depending on elevation and climate and is unstudied in Utah. This research focuses on defining aspects of BWA’s phenology, including the number of annual generations, and exploring an effective detection method to support sustainable management practices.

Bark sampling of infested subalpine fir at five northern Utah study sites was conducted to determine the number of annual generations exhibited by BWA. One full generation and > 50% of a second generation were observed each year with adults in highest abundance in early summer and early fall. Because insect development is dependent on temperature, these data were used in combination with air temperatures recorded at each site to predict the number of annual BWA generations. Using estimated historical and future climate data, the model was used to predict past and future number of generations for northern Utah. Predictions indicated that since 1980, temperatures were suitable for one complete but fewer than two generations at three of the five sites. Within the next several decades, all sites but the warmest are predicted to increase from slightly less than to slightly more than two complete generations. Climate predictions for the warmest site indicate that three complete generations may occur by ~2080.

The use of sticky cards for monitoring immature wind-dispersing BWA was also assessed. Using mesh-covered cards attached horizontally to stakes, crawler captures were high, and bycatch of non-target organisms was low. Timing of crawler abundance peaks aligned with those of bark samples, indicating potential for use in phenological monitoring. These findings will support development of accurate and timely IPM-decision making tools for use by forest managers in the current and future climate of northern Utah.



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