The effect of relative humidity on acaricide efficacy against and dispersal characteristics of the mold mite Tyrophagus putrescentiae A Thesis SUBMITTED TO THE FACULTY OF UNIVERSITY OF MINNESOTA BY Jessica Anne Freitag IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE Advisor: Stephen Kells, PhD June 2013 © Jessica A. Freitag 2013 Acknowledgements I would like to thank the people in my life who helped me complete this work, including my advisor, my committee (Dr. William Hutchison and Dr. Peter Sorensen), my fellow graduate students, the Kells Lab, and my friends. They helped and supported me in many ways—by helping me complete my research, offering guidance, and teaching me along the way. First, I would like to thank my advisor Dr. Stephen Kells for giving me great opportunities to do my research and for teaching me about all kinds of urban pests, their behavior, and management. While most of my research was in the laboratory, Dr. Kells gave me the opportunity to work in the field, to gain a better perspective for my research. Field work also gave me the opportunity to learn how to work with others of varying entomological knowledge, including retail personnel and pest management professionals. This has prepared me to work in many situations and taught me how to communicate with different types of people, including academic, industry, or extension work. Next, I would like to thank my fellow graduate students and lab personnel. Marc Eaton, the lab manager, helped train me and helped with my lab work, offering helpful guidance about procedure along the way. Corey McQueen and Joelle Olson, fellow graduate students, offered some good advice and a lot of emotional support. I would also like to thank my friend Dr. Greg Laden for his guidance as a scientist and his whole- hearted support as a friend. Last, but not least, I would like to thank Nestlé-Purina and Minnesota Pest Management Association for providing funding and support for my research. i Abstract This study determined the effects of relative humidity on mold mites ( Tyrophagus putrescentiae ) with regard to acaricide efficacy and dispersal characteristics. The mold mite is a stored product pest that can be a problem in the retail habitat. Mold mite survival is dependent on relative humidity (RH), so different RH levels were used to determine the efficacy of several commercially available residual acaricides compatible with use in retail operations. To simulate retail shelving, acaricides were applied to Petri dishes and allowed to dry. Mites were placed in dishes, dishes were assigned to one of three RH levels, and mortality was recorded after 24 and 48 hours. Increasing humidity levels generally decreased acaricide efficacy. Resulting efficacy indicated that some residual acaricides may act as an effective barrier against this mite. A second study analyzed the dispersal characteristics of mold mites. Infestations may remain undetected in food sources for long periods, where populations may increase and food sources become depleted, resulting in dispersal of mites to new habitats that have suitable nutrition and humidity. Arenas were designed with an enclosed food reservoir filled with ground dog food and incubated at high humidity. The rest of the arena provided a space for mites leaving the reservoir, and this space was incubated at one of three RH levels. The number of mites leaving the food reservoir was monitored daily until dispersal mode and final population characteristics were determined. In this experiment, mites exhibited explosive dispersal, where migration occurred en masse within 24 h and was dependent on increasing mite density. These findings suggest that direct sampling of habitat may be necessary to detect infestations before explosive dispersal has occurred. ii Table of Contents Acknowledgements ............................................................................................................. i Abstract .............................................................................................................................. ii Table of Contents .............................................................................................................. iii List of Tables ..................................................................................................................... v List of Figures ................................................................................................................... vi Chapter 1. Biology, behavior, and pest management of the mold mite, Tyrophagus putrescentiae (Acari: Acaridae): A review of the literature .............................................. 1 Introduction ....................................................................................................... 2 Taxonomy .......................................................................................................... 7 Life History ....................................................................................................... 7 Physiological and Ecological Considerations ................................................... 9 Integrated Pest Management ........................................................................... 14 Prevention and Control Methods ....................................................... 14 Product Rotation ................................................................................ 15 Sanitation ........................................................................................... 15 Exclusion............................................................................................ 16 Inspection ........................................................................................... 17 Monitoring ......................................................................................... 18 Chemical and Non-chemical Controls ............................................... 19 Conclusion ......................................................................................... 22 Literature Cited ................................................................................................ 24 Chapter 2. Efficacy of selected residual acaricides against the mold mite, Tyrophagus putrescentiae (Acari: Acaridae) ....................................................................................... 33 Summary ......................................................................................................... 34 Introduction ..................................................................................................... 35 Materials and Methods .................................................................................... 38 Results ............................................................................................................. 42 Discussion ....................................................................................................... 49 Literature Cited ................................................................................................ 57 Chapter 3. Explosive dispersal behavior of the mold mite, Tyrophagus putrescentiae (Acari: Acaridae), in relation to relative humidity ........................................................... 61 Summary ......................................................................................................... 62 Introduction ..................................................................................................... 63 Materials and Methods .................................................................................... 66 Results ............................................................................................................. 70 iii Discussion ....................................................................................................... 81 Literature Cited ................................................................................................ 85 Thesis References ............................................................................................................ 89 iv List of Tables Chapter 2 Table 1. Characteristics of selected residual acaricides used in the study .................40 Table 2. Summary of analysis of variance for factors affecting efficacy of selected residual acaricides against mites .................................................................43 Table 3. Summary of analysis of variance for factors affecting efficacy of selected residual acaricide applications against mold mites .....................................47 Chapter 3 Table 1. Age distribution at final day of study, or after explosive dispersal event ...73 Table 2. Minimum and maximum counts in arena by location, stage of mite, and humidity level in the arena ..........................................................................74 Table 3. Mite density in reservoir and total mites in arena as a function of mass of food in the reservoir at time of explosive dispersal .....................................75 v List of Figures Chapter 2 Figure 1. Mean proportion mortality of T. putrescentiae 24 h after exposure to selected acaricides, at three relative humidities. ........................................44 Figure 2. Mean proportion mortality of T. putrescentiae 48 h after exposure to selected acaricides, at three relative humidities. ........................................45 Figure 3 . Mean proportion mortality of T. putrescentiae 48 h after exposure to selected acaricides at 68% RH. ..................................................................48