Host Colonization Behavior of the Walnut Twig Beetle, Pityophthorus juglandis Blackman, in California Hinds Walnut Andrew Graves, Stacy Hishinuma, Shakeeb Hamud and Steven Seybold
Presentation Outline - Thousand Cankers Disease (Geosmithia)and (twig beetles) Pityophthorus - Pityophthorus sp. and disease associations - Geosmithia spp./ bark beetle interactions - Pityophthorus juglandis identification and distribution in CA - Impacts of Thousand Cankers Disease in CA - Bark beetle semiochemistry and our research
Distribution of Walnut Twig Beetle/Thousand Cankers Disease Complex Ned A. Tisserat, Colorado State University, Fort Collins, has isolated Geosmithia sp. from walnut trees growing in these states. Widespread tree mortality has occurred in CA, CO, ID, NM, OR, and UT.
Twig beetles (Pityophthorus spp.) Typically not considered forest pests due to mechanical damage. May be more important as disease vectors. Pitch canker, Fusarium circinatum Scleroderris Canker, Gremmeniella abietina Leptographium root disease, Leptographium procerum
Geosmithia bark beetle interactions Associated with 30 + species of bark beetles and numerous other subcortical insects Found in association with other vectors and ambrosia beetles in tropical areas of the Americas, Asia, and Australia The seven known species are found primarily in association with bark beetles and their galleries. Kolarik et al., 2007, 2008
Walnut twig beetle identification Pityophthorus juglandis Two rows of tubercles Concentric arcs of asperities
Pityophthorus juglandis in California commercial Museum surveys and collections from CA (2008) California Academy of Sciences California Department of Food and Agriculture, UC-Davis and UC-Berkeley Records show presence in: Los Angeles Co. (1950's) Butte, Lassen, and San Mateo Cos. (1970's) Sacramento Co. (1982) P. juglandis is not a recent introduction and is very likely a native species in California
English walnut root stock is derived from Juglans hindsii or a J. hindsii x J. regia hybrid CA produces 95% of English walnuts grown in the U.S; value of commercial crop was $563 million in 2006 (USDA-NASS, 2008).
Insects associated with P. juglandis in Juglans hindsii in CA. Xylotrechus nauticus (Col.: Cerambycidae): oak cordwood borer (phloem/xylem feeder) Scobicia declivis (Col.: Bostrichidae): false powerpost beetle (xylem feeder) Temnochila chlorodia (Col.: Trogositidae): generalist predator Unknown (Col.: Laemophloeidae): generalist predator Unknown (Col.: Monotomidae): generalist predator Neocalosoter sp. (Hymenoptera: Pteromalidae): parasitoid of P. juglandis Plastanoxus westwoodi (Hymenoptera: Bethylidae): parasitoid of P. juglandis
Thousand Cankers Disease-Symptoms Juglans hindsii: Flagging Branches Juglans californica: Bark Staining Geosmithia sp. conidia and conidiophores Sycamore X Cassel, Davis, Yolo Co., CA UCD Wolfskill Exp. Farm, Winters, Yolo Co., CA
Impact: Thousand Cankers Disease-Walnut Twig Beetle Juglans californica: Near Piru Lake, Ventura Co. Juglans hindsii: Along Putah Creek, near Winters, Yolo Co.
Impact: Thousand Cankers Disease-Walnut Twig Beetle Juglans hindsii: Sycamore X Cassel, Davis, Yolo Co. Juglans hindsii: Pedrick Road, Davis, Yolo Co.
Host Colonization by Bark Beetles Accept host tree: feed, release pheromones (concentration phase), mate, oviposit (establishment phase) Short-range olfaction and/or gustation Dispersing beetles search for host tree No Correct species? Yes No Presence of heterospecifics? Colonization density/duration? Yes Yes Presence of conspecifics? Colonization density/duration? No No Susceptible? Yes Graves et al. 2008
Objectives-Host Selection Determine the timing and pattern of host selection Determine which sex initiates host colonization
Experimental Design Determine the timing of host selection Determine which sex initiates host colonization uninfested J. hindsii branches were hung near an urban forest each day, branches were checked for entrance holes branches were dissected and the sexes of beetles in galleries were determined
Results Determine the timing and pattern of host selection Walnut twig beetles fly in the early evening (usually between 6 and 9 PM) Late July initial evidence for attack, 4 d after placement 15 galleries identified on 16 branches 9/15 galleries were initiated between 6-9 d
Results Determine which sex initiates host colonization Males initiate colonization of walnut branches. 1 1 1 + 1 1 + 2 No. of galleries 7 0 6 2 Males colonize first Joined by 1-2 females, transverse galleries
Field Collections Experimental Design infested branches were collected from J. californica branches were subsampled (20 cm lengths) and the number and location of galleries were determined USDA-ARS National Clonal Germplasm Repository (Winters, CA)
Results Determine the timing and pattern of host colonization Prefers branches > 1.5 cm in diameter
Results Determine the timing and pattern of host colonization Constructs entrance holes on or around leaf scars or lenticels (leverage?).
Objectives-Pheromone Biology Determine the attractive aggregation pheromone
Experimental Design-Pheromone Biology
Experimental Design Determine who makes the attractant. 1) 100 + 100 mixed 2) 100 + 100 separate 3) 100 alone 4) 100 alone 5) Walnut branches (J. hindsii) mixed separate
Experimental Design 3) Determine the interaction between the sexes and production of the attractant. 100 + 100 Mixed a a 100 + 100 Separated a a 100 Alone b b 100 Alone Walnut branches c c c c 40 30 20 10 10 20 30 40 Male response Female response No. of P. juglandis per day (mean ± S.E.) Males: F=9.25; P<0.001 Females: F=20.33; P<0.001 Total Trap Catch: 1097 (402 male/695 female) 4-17 September 2008, Davis, Yolo Co., CA
Summary-Host Selection Insects find freshly cut branches within 4-9 d Prefer branches > 1.5 cm in diameter Prefer colonizing on or near leaf scar Male P. juglandis initiate host colonization
Summary-Pheromone Biology Males produce an attractive aggregation pheromone. Increased colonization density by males increases the attractiveness of infested branches to females. The addition of females (mixed or separated) to male-infested logs synergizes the attractiveness of infested branches. In Late July and September in CA, P. juglandis fly in the early evening (usually between 6 and 9 PM).
Current and Future Studies Identifying the specific compounds that are involved in the aggregation behavior for use in monitoring programs Determining the diurnal and seasonal flight periodicity Developing repellent semiochemicals for use in management programs Target compounds will include: pityol, grandisol, conophthorin, and vittatol
Walnut Twig Beetle Work Acknowledgments Ned Tisserat (fungal identifications) Tom Coleman (field collections) Chuck Leslie (field collections and walnut identification) Zach Heath and Meghan Woods (aerial survey and mapping)
Thank you