Integrating biological control and chemical control of cabbage caterpillar pests THESIS Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University By Emily Kathryn Linkous Graduate Program in Entomology The Ohio State University 2013 Master's Examination Committee: Dr. Celeste Welty (advisor) Dr. Mark A. Bennett Dr. Mary M. Gardiner Dr. Luis A. Cañas Copyrighted by Emily Kathryn Linkous 2013 Abstract Lepidopteran pests Plutella xylostella, Pieris rapae, and Trichoplusia ni are the major species that attack crops in the family Brassicaceae. They are typically controlled by insecticide application, but there are parasitoid species that contribute to mortality. However, parasitoids alone are typically unable to exert sufficient control to reduce pest numbers below economic thresholds. Pest density tends to be lower in more diverse systems, including those that integrate flowering plants that parasitoids use as food resources. These resources are lacking in most agricultural landscapes. Parasitoids tend to be negatively impacted by exposure to broad-spectrum insecticides. The first goal of this research was to investigate the integration of habitat manipulation and insecticide treatment through the planting of floral resources and use of selective microbial insecticides. The integration of sweet alyssum (Lobularia maritima) insectary strips and the insecticide Bacillus thuringiensis (B.t.) was investigated in a cabbage field trial conducted in 2011 and 2012. The results of this study are discussed in Chapter 2. The objectives of this study were: 1) to determine the effects of insectary strips on parasitism rates and pest density; and 2) to determine the effects of insecticides on parasitism rates and pest density. The main plot treatment was the presence or absence of insectary strips and the subplot treatment was insecticide. Plots were sampled weekly. Insectary strips were found to have no significant effect on pest density in or parasitism in 2011. In 2012, insectary strips were found to have increased pest density but also ii increased parasitism. Parasitism rates were lower in subplots treated with B.t. than in untreated subplots. Pest density in subplots treated with B.t. was not significantly different than subplots treated with cyfluthrin. These findings indicate that insectary strips can increase parasitism but may also increase pest density in some circumstances. The use of microbial insecticide did not increase parasitism but did keep pest density low. Because parasitism appeared to be density dependent, use of lower rates or longer intervals of B.t. may increase parasitism while maintaining low pest density. Another goal of the research was to determine what parasitoid species were present in Ohio. The diversity and relative abundance of parasitoid species found in the survey are discussed in Chapter 3. The objectives of this study were: 1) to determine parasitoid diversity and parasitism rate on commercial farms; and 2) to determine whether differences in parasitism rates among farms are associated with differences in insecticide use as measured by the environmental impact quotient (EIQ). Ten commercial fields were used for the surveys in 2011 and 2012. Caterpillars were collected and held until the emergence of parasitoids or pests. Eleven parasitoid species were found. Species abundance varied between years. Farms with a higher EIQ rating tended to have decreased species abundance and percent parasitism, but this correlation was not significant. These findings indicate that many species of parasitoids are present in Ohio and that insecticide usage can impact parasitoid species diversity and abundance. Diadegma insulare and Cotesia rubecula should be the primary target of conservation biocontrol tactics within integrated pest management programs for cabbage. iii Dedicated to my wonderful friends and family and the love of my life. iv Acknowledgments I would like to thank my advisor, Dr. Celeste Welty, for her support, guidance, and enthusiasm. I also thank my committee for their helpful feedback throughout my research project and Zhiguang Xu for his assistance with the statistical analysis of my data. My research project would not have been possible without the work of the farm crews at the North Central Agricultural Research Station in Fremont, Ohio, the Waterman Agricultural and Natural Resources Laboratory in Columbus, Ohio, and the Muck Crops Agricultural Research Station in Celeryville, Ohio. My field assistants Amanda Lord, Jeremy Wells, Greg Holthaus, Ryan Caesar, and Mackenzie Dorner were essential for the efficient collection of data, no matter what the weather was like. I thank Stan Gahn and Mark Koenig for their assistance in finding cabbage fields for my survey. I also thank my colleagues, friends, and family for their unending support during my graduate school career. Thanks for being a sounding board or letting me vent. Special thanks to my loving boyfriend Justin Franzen for keeping me sane and always being there to help me through the rough times. This research would not have been possible without my funding sources – thanks to SEEDS at OARDC and the Ohio Vegetable and Small Fruit Research and Development Program for financial support. v Vita May 2006 ......................................................Wilmington High School May 2010 .......................................................B.S. Biology, Wittenberg University 2010 to present ..............................................Graduate Teaching Associate, Center for Life Sciences Education, The Ohio State University Fields of Study Major Field: Entomology vi Table of Contents Abstract ............................................................................................................................... ii Acknowledgments............................................................................................................... v Vita ..................................................................................................................................... vi List of Tables ...................................................................................................................... x List of Figures .................................................................................................................... xi Chapter 1: A review of previous research on biological control and chemical control of cabbage pests ...................................................................................................................... 1 1.1 Introduction ............................................................................................................... 1 1.2 Objectives .................................................................................................................. 4 1.3 Biology and ecology of Lepidopteran cabbage pests and their common parasitoids........................................................................................................................ 6 1.4 A review of the proposed hypotheses and the theoretical basis for the research .... 10 1.5 Previous research on floral resources, pesticides, and natural enemies, and their integration into control programs .................................................................................. 14 1.6 Previous research on parasitoid diversity and abundance in cole crops in North America ......................................................................................................................... 19 vii 1.7 References ............................................................................................................... 22 Chapter 2: Integrating alyssum insectary strips and selective insecticides in cabbage .... 31 2.1 Introduction ............................................................................................................. 31 2.2 Methods ................................................................................................................... 34 2.2.1 Field trials at agricultural research stations ...................................................... 34 2.2.2 Harvest evaluation ............................................................................................ 38 2.2.3 Alyssum vacuum sampling ............................................................................... 38 2.2.4 Data analysis ..................................................................................................... 39 2.3 Results ..................................................................................................................... 40 2.3.1 Caterpillar density............................................................................................. 40 2.3.2 Parasitism.......................................................................................................... 41 2.3.3 Harvest .............................................................................................................. 43 2.3.4 Alyssum vacuum sampling ............................................................................... 44 2.4 Discussion ............................................................................................................... 45 2.5 References ............................................................................................................... 47 2.6 Tables .....................................................................................................................