HOST SELECTION BY THE WALNUT TWIG BEETLE, PITYOPHTHORUS JUGLANDIS, IN CALIFORNIA ____________ A Thesis Presented to the Faculty of California State University, Chico ____________ In Partial Fulfillment of the Requirements for the Degree Master of Science in Biological Sciences ____________ by Irene Lona Spring 2019 HOST SELECTION BY THE WALNUT TWIG BEETLE, PITYOPHTHORUS JUGLANDIS, IN CALIFORNIA A Thesis by Irene Lona Spring 2019 APPROVED BY THE INTERIM DEAN OF GRADUATE STUDIES: ________________________________ Sharon Barrios, Ph.D. APPROVED BY THE GRADUATE ADVISORY COMMITTEE: ________________________________ Donald G. Miller, Ph.D., Chair ________________________________ Colleen Hatfield, Ph.D. ________________________________ Richard Rosecrance, Ph.D. ________________________________ Steven J. Seybold, Ph.D. TABLE OF CONTENTS PAGE List of Tables ............................................................................................................. iv List of Figures ............................................................................................................ v Abstract ..................................................................................................................... vi CHAPTER I. Host selection behavior mediated by differential landing rates of the walnut twig beetle, Pityophthorus juglandis Blackman (Coleoptera: Scolytidae), on two western North American walnut species, Juglans californica and Juglans major .................. 1 Abstract ........................................................................................... 2 Introduction .................................................................................... 4 Materials and methods .................................................................... 7 Results............................................................................................. 14 Discussion ....................................................................................... 22 Acknowledgements ......................................................................... 27 References ...................................................................................... 28 II. Effect of water stress on the susceptibility of commercial English walnut, Juglans regia, to the walnut twig beetle, Pityophthorus juglandis ........................................ 45 Abstract .......................................................................................... 46 Introduction ..................................................................................... 48 Materials and methods ..................................................................... 50 Results............................................................................................. 58 Discussion ....................................................................................... 63 Acknowledgements ......................................................................... 68 References ....................................................................................... 68 iii LIST OF TABLES TABLE PAGE 1.1 Synthesis of measures of host susceptibility to walnut twig beetle, Pityophthorus juglandis, feeding and Geosmithia morbida inoculation from the literature ..... 33 1.2 Subcortical insect associates and predators of walnut twig beetle, Pityophthorus juglandis, trapped during flight monitoring at the NCGR ................................ 34 1.3 Subcortical insect associates and predators of walnut twig beetle, Pityophthorus juglandis, trapped during flight monitoring at the ATRC................................. 35 1.4 Landing rates of insects associated with Pityophthorus juglandis, Juglans spp., and other hardwood trees on acetate sticky sheets .......................................... 36 1.A Accession numbers of branches collected from Juglans californica and Juglans major trees ...................................................................................................... 43 2.1 Temperature, humidity, and baseline potential recorded during the dates when stem water potential (SWP) was measured on English walnut ......................... 73 2.2 Number of main branches and twigs for each diameter class and number of sections with Pityophthorus juglandis entrance/emergence holes and Nathrius brevipennis or Gildoria sp. emergence holes ................................................... 74 2.3 Total number of insects trapped in two funnel traps each baited with an ethanol lure and two unbaited funnel traps (controls) ................................................... 75 iv LIST OF FIGURES FIGURE PAGE 1.1 Branch sections of two Pityophthorus juglandis host plants used in the flight landing assays 1-4: Juglans major and Juglans californica ............................. 37 1.2 Cardboard tube used as negative control ............................................................ 37 1.3 Juglans branch section surrounded by a mesh screen bag and adhesive-coated acetate sheet .................................................................................................... 38 1.4 Walnut twig beetle, Pityophthorus juglandis, flight at NCGR and ATRC........... 39 1.5 Weekly landing rates of male and female walnut twig beetle, Pityophthorus juglandis, female Xyleborinus saxeseni, female Hypothenemus eruditus, and male and female Nathrius brevipennis (Assays 1-4) ........................................ 41 1.6 Weekly landing rates of male and female walnut twig beetle, Pityophthorus juglandis, female Xyleborinus saxeseni, and female Hypothenemus eruditus (Assay 5) ........................................................................................................ 42 2.1 Juglans regia branch with lure of male Pityophthorus juglandis aggregation pheromone ...................................................................................................... 76 2.2 Juglans regia branch divided into sections of 27 cm .......................................... 77 2.3 Branch of Juglans regia with Pityophthorus juglandis entrance and emergence holes ............................................................................................................... 78 2.4 Twig from Juglans regia branch with Nathrius brevipennis and Gildoria sp. emergence holes ............................................................................................. 78 2.5 Stem water potential of trees in the low water stress group, high water stress group, and control group ................................................................................. 79 2.6 Stem water potential of baited and unbaited branches ........................................ 80 2.7 Frequency distribution of Pityophthorus juglandis entrance or emergence holes by distance from the aggregation pheromone lure ........................................... 81 2.8 Number of Pityophthorus juglandis entrance or emergence holes on four aspects (top, left, right, and bottom) ............................................................................ 82 2.9 Distribution (by branch or twig diameter) of entrance or emergence holes from Pityophthorus juglandis, and emergence holes from Nathrius brevipennis and Gildoria sp. .................................................................................................... 83 2.10 Number of Nathrius brevipennis emergence holes in relation to the distance from the lure of male Pityophthorus juglandis aggregation pheromone ................... 85 2.11 Number of Gildoria sp. emergence holes in relation to the distance from the lure of male Pityophthorus juglandis aggregation pheromone ................................ 86 2.12 Flight response of female Xyleborinus saxeseni and male and female Nathrius brevipennis to two ethanol-baited and two unbaited traps ................................ 87 v ABSTRACT HOST SELECTION BY THE WALNUT TWIG BEETLE, PITYOPHTHORUS JUGLANDIS, IN CALIFORNIA by Irene Lona Master of Science in Biological Sciences California State University, Chico Spring 2019 Walnut (Juglans) and wingnut (Pterocarya) trees have been declining in response to Thousand Cankers Disease (TCD). The TCD pathogen, Geosmithia morbida, is vectored by a phloeophagous bark beetle, the walnut twig beetle (Pityophthorus juglandis Blackman). To understand P. juglandis host selection, the following were investigated at two orchards in Northern California: 1) The susceptibility of two walnut species (Juglans californica and J. major) native to the western USA by comparing P. juglandis flight and landing responses to unbaited branch sections and 2) The relationship between English walnut (Juglans regia) tree health, represented by several levels of plant water stress, and P. juglandis colonization success. P. juglandis preferred to land on J. californica over J. major. With J. regia, there was no significant difference in P. juglandis activity between branches from trees in high water stress and low water stress groups (both baited with P. juglandis aggregation vi pheromone). No P. juglandis colonization activity was observed in unbaited branches from the negative control group (unbaited). Activity by P. juglandis was found primarily on 4 cm diameter branches. Other invasive bark and ambrosia beetles such as Hypothenemus eruditus and Xyleborinus saxeseni; and an invasive longhorned beetle, Nathrius brevipennis preferred to land on J. major over J. californica. Collections of H. eruditus and an invasive ambrosia beetle, Xyleborus affinis, in Butte County reflect the northernmost records of these