Regional and Local Drivers of Mason Bee (Genus Osmia) Decline Across the Eastern Seaboard
Total Page：16
File Type：pdf, Size：1020Kb
REGIONAL AND LOCAL DRIVERS OF MASON BEE (GENUS OSMIA) DECLINE ACROSS THE EASTERN SEABOARD A Dissertation Presented to the Faculty of the Graduate School of Cornell University in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy by Mary Louise Centrella August 2019 © 2019 Mary Louise Centrella REGIONAL AND LOCAL DRIVERS OF MASON BEE (GENUS OSMIA) DECLINE ACROSS THE EASTERN SEABOARD Mary Louise Centrella, Ph.D. Cornell University 2019 Though there has been much focus on honey bee (Apis mellifera L.) decline, wild bees, which are essential to both ecosystem functioning and crop pollination, are also facing declines across Europe and North America. Potential drivers of theses declines include competition with non-native species, landscape simplification, increased pesticide risk, and reduced diet diversity. Here, I ask 1. how an introduced wild bee impacts a closely related, native congener at a regional scale, 2. how landscape simplification, diet diversity, and pesticide risk interact to impact wild bee populations in apple agroecosystems, and 3. how pesticide risk levels compare between wild bees and honey bees in the same apple orchards during bloom. To assess the impact of non-native Osmia cornifrons on the decline of native O. lignaria across the Eastern Seaboard, Ie used historical specimen records from 36 insect collections over 120 years. I found no evidence that O. cornifrons influenced O. lignaria decline; instead, their abundance (relative to other bees) has been decreasing since 1890, long before the 1977 introduction of O. cornifrons. Next, I was interested in exploring the drivers of Osmia performance in agroecosystems. Due to limited availability of O. lignaria, I assessed the response of nesting female O. cornifrons to landscape simplification, pesticide risk, and floral diet diversity in 17 NY apple orchards in 2015. In simplified landscapes, O. cornifrons produced fewer female offspring that weighed less, via reduced diet diversity and increased fungicide risk levels from Rosaceae (likely apple) pollen. Reductions in female offspring number and weight could lead to O. cornifrons population decline over time, as smaller-bodied bees produce fewer offspring and have shorter life-spans, suggesting that further studies of wild bee declines should focus on landscape simplification, pesticide risk, and floral diet diversity as potential drivers. To assess whether the historic use of honey bees as models for wild bee decline is adequate, I directly compared one driver of bee decline, pesticide risk levels, in O. cornifrons and A. mellifera pollen in 14 apple orchards during bloom in 2015. For O. cornifrons, increasing apple land cover resulted in increased pesticide risk levels in their pollen provisions, via increased Malus (crop) pollen collected. However, these relationships were not significant for honey bees, suggesting that their use as a model for all bee species may lead to inaccurate assessments of pesticide risk to some wild bee populations in agroecosystems. My results show that Osmia lignaria decline is not necessarily exacerbated by Osmia cornifrons at the regional scale. At the local scale, I show that landscape simplification, increased pesticide risk, and reduced diet diversity could potentially lead to O. cornifrons population decline, via reduced offspring number and size. Finally, I show that it is essential to continue studying the drivers of wild bee decline, as honey bees do not provide an adequate model with which to assess health of all bee species. By continuing to research the underlying causes of wild bee decline at both the regional and local scales, we can better preserve these important pollinators. BIOGRAPHICAL SKETCH Mary Centrella has always been passionate about nature, a passion born in the big skies, vast plains, and beckoning mountains of wild Wyoming. At the University of Wyoming, from which she received a Bachelors of Arts in Spanish and a Bachelors of Science in Zoology in 2013, she was lucky to meet Dr. Scott Shaw and Dr. Michael Dillon, both of whom left big impressions on her future career by sparking her interest in wasps and bees. During her time as graduate student at Cornell University, Mary has created a project that helps to bridge the gap between multiple scientific fields. At Cornell, Mary discovered her true calling: sharing science with others through outreach and extension. She is poised for a career bridging the gap between scientific research and the community and will be starting as the Director of the Pesticide Management Education Program for New York State in the fall. Through her research, Mary works to understand the drivers of mason bee decline, so that we can preserve the health and biodiversity of our important wild bee pollinators. During her undergraduate degree, Mary was a Goldwater Scholar, and as a graduate student, she received the National Science Foundation Graduate Research Fellowship. Mary is grateful for these awards, as they have helped her to achieve her academic and career goals. While at Cornell, Mary served as a Fellow for the Center for Teaching Excellence and was also a mentor for the LGBT Resource Center. She has enjoyed extension and outreach activities, such as building bee nests with the community at Judy’s Day, and presenting her research to the Apple Research Development Program. One of her favorite moments was returning to the AMK Research Station in Grand Teton National Park, where she once worked as a maintenance woman, to speak about bee decline and biodiversity to over 150 park workers, community members, and scientists. iii ACKNOWLEDGEMENTS I am incredibly grateful to have had the opportunity to be a graduate student here at Cornell, in the Department of Entomology. The students, faculty, and staff have been instrumental in supporting me and I have come to regard many of them as close friends and talented collaborators. I am also grateful to the Ithaca community, which accepted me with open arms. I could not have achieved this work without the constant support of my friends and family, who are scattered all over the globe, and, of course, the patience and compassion of my amazing fiancée. I feel very lucky to have had such a talented team of advisors. Thank you, Bryan, for your patience as you guided me to become a better writer and speaker. Thank you for all the opportunities you offered me, from allowing me to instruct a course with you in the tropics, to introducing me to leading researchers in our field at the Entomological Society of America. You are incredibly generous with your funding, your time, and your talent. You have cultivated a lab full of strong, warm, and smart scientists from whom I have benefitted immensely and with whom I will always be friends. You have taught me how to tell a story and your passion for wild bees has been a great motivator during my time in your lab. Thank you Katja, for supporting me, not only in my thesis research, but also in my development as a scientist, and in my personal growth during these six transformative years. From assembling a team of people to help move hundreds of plants for my experiment, to orchestrating a lab-wide publication, your passion for science and your ability to motivate people has been inspiring. You have developed a collaborative, engaging lab full of gifted colleagues whom I will miss dearly. My project would have been impossible without your statistical prowess and expertise in experimental design. Most importantly, you have taught me how to be flexible when projects flounder, to “listen” to my data, and to stay optimistic and engaged in research. iv I want to thank both Bryan and Katja for working so well as team. It was the combination of your talents and your ability to work well with each other that made this project, and truly my career, so successful. This thesis is a tribute to the support and advice of my committee members, Jeff and Scott. Jeff, you hold everyone to a high scientific standard, but you also give them the tools to meet these expectations. I feel lucky to have had you as teacher and I have learned so much about toxicology from you. You inspired me to be passionate about pesticides, a subject I had minimal knowledge of before coming to New York. I have always appreciated your candid attitude, and the advice you give improves not just my research, but my understanding of science. Scott, I have enjoyed collaborating with you immensely. You have the unique ability to pull together ideas from many different fields and you are always willing to share with others. Your dedication to pairing excellent research with equally vigorous extension and dissemination of that knowledge really sets you apart. I want to thank my entire committee. Jeff, Scott, Bryan, and Katja, you have helped me create a project that encompass a variety of fields of research and you have given me the tools and the confidence to pursue a career in scientific extension. I look forward to continuing to learn from all of you in the future. v TABLE OF CONTENTS Biographical Sketch ...................................................................................................................................... iii Acknowledgements ...................................................................................................................................... iv Table of Contents ......................................................................................................................................... vi Chapter 1. Range