Biology and population dynamics of the eastern larch beetle, Dendroctonus simplex LeConte, and its interactions with eastern larch (tamarack), Larix laricina. A DISSERTATION SUBMITTED TO THE FACULTY OF THE UNIVERSITY OF MINNESOTA BY Fraser Ray McKee IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Brian H. Aukema, Ph.D. Advisor September 2015 © Fraser Ray McKee 2015 Acknowledgements I would first like to extend my sincere gratitude to my advisor, Dr. Brian Aukema. Brian, we have worked together a long time. For almost eight years you have always provided a positive, productive, and exceptional learning experience for all of your students. Your open door policy, positive attitude, attention to detail, encouragement, and counsel have allowed me to achieve my academic goals. You have been a great advisor and friend. I will miss spending time with you, Kelly, James and Garrett. I also thank my committee members Drs. Anthony D’Amato, Stephen Kells, and Robert Venette for volunteering your time, guidance, and expertise. Your advice and insight has greatly improved this dissertation. To Jana Albers, Michael Albers, and Valerie Cervenka. (Minnesota Department of Natural Resources – Forestry), your continual interest in this project and eagerness to see it succeed was humbling. Thank you for everything you have done to help me with this project. Thank you to Audrey Zahradka, Erica Nystrom, Michelle Cummings, Jonah Widmer, and Aubree Wilke for all your hard work and positive attitudes when helping with fieldwork, processing samples, and maintaining experiments. Special recognition is also given to Ewing Teen who voluntarily took time away from writing his thesis to work with me for three days in continual rain and mosquito-infested bogs so that I could set this project up as quickly as possible. I was fortunate to have as my officemates Samuel Fahrner, Andrea Hefty, Derek Rosenberger, Aubree Wilke, Marissa Streifel, and Rachael Nicoll. I enjoyed all the time we have spent together. Thank you for your support, assistance, and friendship. I wish each of you the best in all of your endeavors. To the friends I have made at the University of Minnesota, the Red Lake Wildlife Management Area, and elsewhere – thank you for all the great memories. Jeff, Gretchen, Josh, and Johanna Birchem-Mehmel – what a special family you are. It was a pleasure getting to know each of you over the past several years. Your endless generosity, kindness, and humor transformed the time I spent in field camp into a unique experience. Jeff, thank you for the camaraderie, the hunting opportunities, and willingness to i pass on your knowledge of the outdoors and of ethical sportsmanship. Gretchen, I will always remember your thoughtfulness, such as remembering my birthday during field season, baking a cake, and arranging a celebration, despite having a dozen other things to do. Josh, our conversations and debates enlivened many evenings. Johanna, your inquisitive personality and free spirit always made me smile. To each of you – thank you so much for welcoming me into your lives. I wish you all the very best in the future. Renata, I cannot put into words the gratitude I have for your unwavering support, forbearance, understanding, and encouragement. Your positive attitude, optimism, and character are to be admired. You were always there to help me put issues into perspective and you have helped me through many tough times. Thank you so very much. Finally, and with tremendous gratitude, I thank my parents Cherolyn and Stephen for providing steadfast support and understanding, and for instilling in me the value of hard work, determination, dedication, and fortitude. I also thank the rest of my family, Ryan, Pam, Mathew, Becky, Courtney and Jason for always keeping in touch and including me in your lives during the years that I have been away, that has been extremely important to me. Thank you to everyone for all of your encouragement, patience, and support throughout this entire process. ii Dedication To my nephew Liam, and nieces Clara, Reese, and Libby. May you always achieve your goals. iii Abstract The range of the eastern larch beetle, Dendroctonus simplex LeConte (Coleoptera: Scolytinae), is concomitant with its primary host, eastern larch (tamarack), Larix laricina (Du Roi) K. Koch, throughout the North American boreal forest. Since 2000, an ongoing outbreak of eastern larch beetles in the south-central part of tamarack’s range throughout the Great Lakes region has caused extensive mortality to mature tamaracks, affecting over 86,500 hectares of tamarack forest in Minnesota. Extended outbreaks in live trees are atypical of this insect, so the eastern larch beetle’s biology and ecology were studied under laboratory and field conditions in Minnesota from 2011 – 2014 to decipher the factors contributing to this ongoing outbreak. In the laboratory, the minimum and optimal developmental temperatures for eastern larch beetles were determined to be 7.5 and 27.9°C, respectively. Some progeny were able to reproduce in the absence of an overwintering period, suggesting that a reproductive diapause may not be obligate in all individuals. This was confirmed by field studies, which found that a second generation of eastern larch beetles successfully completed development during the summer and fall of 2012. Confirmation of two generations instead of three sibling broods established by re-emerging parents in one year was established by detailed phenological and physiological methods. As beetle infestations progressed through tamarack stands, beetles initially preferred to attack the largest tamaracks before killing smaller hosts at random in successive years. Reproductive success of females increased in larger and older tamaracks, and those “challenged” by unsuccessful attacks in the recent past. Higher concentrations of resin pockets within the phloem consistently reduced beetle reproduction. The size of male and female beetle offspring, as well as the total lipid content of female offspring, increased with tamarack size and phloem thickness. Development within “challenged” tamaracks reduced both the total and proportional lipid contents of all beetle offspring. New understandings of the population dynamics of eastern larch beetles are discussed. Expanding growing seasons, for example, may facilitate fractional voltinism, or, two generations in one year, among a portion of the population. Synchronous beetle emergence the following iv spring – shown in phenological studies – would enhance host procurement, especially of the largest and most preferred hosts that produce the most vigorous offspring, thus exacerbating the outbreak. v Table of Contents Acknowledgements. i Dedication. iii Abstract. iv List of Tables. xiv List of Figures. xvi Introduction. xxii Chapter 1. Literature review of previous research on the eastern larch beetle Dendroctonus simplex LeConte (Coleoptera: Scolytinae). 1.1 Host species. 1 1.2 Factors associated with the increased tree-killing activity of eastern larch beetles. 2 1.3 Eastern larch beetle identification. 5 1.4 Life cycle. 7 1.4.1 First brood. 8 1.4.2 Second Brood. 9 1.4.3 Third brood. .10 1.5 Host colonization. 11 1.6 Mating behavior. .13 1.7 Oviposition and brood development. 14 1.8 Over-wintering biology. 16 1.9 Chemical ecology. 17 1.10 Fungal associates. 21 1.11 Competitors of eastern larch beetles. 22 1.12 Natural enemies. 23 1.13 Characteristics of tamaracks infested by eastern larch beetles. 24 1.14 Host selection with respect to tree size. 27 1.15 Impacts of eastern larch beetles on tamarack stand structure. 28 vi 1.16 Tamarack defense. 29 1.17 Management of eastern larch beetles. 31 1.18 Figures. 33 Chapter 2. Influence of temperature on the reproductive success, brood development, and brood fitness of the eastern larch beetle, Dendroctonus simplex LeConte. 2.1 Summary. 35 2.2 Introduction. 35 2.3 Materials & Methods. 39 2.3.1 Source of experimental tamarack material. 39 2.3.2 Source of parent eastern larch beetles. 39 2.3.3 Preparation of material for breeding experiments. 39 2.3.4 Colonizing billets with parent eastern larch beetles and collection of brood adults. 40 2.3.5 Rearing temperature treatments. 41 2.3.6 Measuring the effect of temperature on beetle reproduction, brood development, and brood fitness. 42 Brood sex ratio and number of brood per parent female. 42 Beetle development time and development rate. 42 Optimal and minimum temperature for brood development. 43 Degree days required for beetle development. 43 Brood adult size and lipid content. 43 2.3.7 Statistical analyses. 44 2.4 Results. 45 2.4.1 Number of brood produced per parent female and brood sex ratio. 45 2.4.2 Beetle development time and optimal developmental temperature. 45 2.4.3 Beetle development rate and minimum developmental temperature. 45 2.4.4 The effect of rearing temperature on offspring size and dry mass. 46 2.4.5 The effect of beetle dry mass on total and percent lipid content. 46 2.4.6 The effect of rearing temperature on the total and percent lipid content of offspring. 47 vii 2.4.7 Number of degree days needed for eastern larch beetle development. 47 2.5 Discussion. ..