Host selection behavior mediated by differential landing rates of the walnut twig beetle, Pityophthorus juglandis, and associated subcortical insect species, on two western North American walnut species, Juglans californica and J. major

Abstract

The walnut twig beetle, Pityophthorus juglandisBlackman (Coleoptera: Scolytidae), vectors a phytopathogenic fungus, Geosmithia morbidaKolařík et al. (Hypocreales), which causes thousand cankers disease (TCD) in walnut (Juglanssp.) and wingnut (Pterocaryasp., both Juglandaceae) trees. We investigated an early point in disease inception in two walnut species – Juglans californicaS. Wats. and Juglans major(Torr. ex Sitsgr.) Heller – native to riparian forests of the western USA by comparing P. juglandisflight and landing responses to small‐diameter branch sections. Twenty unbaited branch sections (10 each of J. californicaand J. major) were presented in a completely randomized design to populations of P. juglandisat the USDA Agricultural Research Service, National Clonal Germplasm Repository (NCGR) Juglanscollection located at Wolfskill Experimental Orchards (Winters, CA, USA) and at the California State University, Chico, Agricultural Teaching and Research Center (ATRC, Chico, CA). These assays were carried out within a 4‐ to 6‐year period when weekly flight surveys with aggregation pheromone‐baited multiple funnel traps revealed that P. juglandisflight activity–abundance was higher at the NCGR than at the ATRC. For the landing rate assays, adhesive‐coated acetate sheets were wrapped around the branch sections and exchanged weekly. Three assays were completed at the NCGR (assays 1–3), whereas one assay was completed at the ATRC (assay 4). Landing rates on these traps were compared between J. californicaand J. major. Two additional assays (5 and 6) were completed at the NCGR to compare responses to branch sections of J. californicaand to similarly sized cardboard tubes (negative control). All six assays were completed over a 4‐year span during the 4‐ to 6‐year weekly flight survey period. Pooled landing rates of male and female P. juglandis(assays 1–4) demonstrated a preference by both sexes for J. californicaover J. major.In assay 5 there was no preference by males or females for J. californicaover the negative control, perhaps due to the low flight activity–abundance of P. juglandisduring the assay. When repeated at a time of higher flight activity–abundance (assay 6), male and female landing rates on J. californicaexceeded those on the negative control. Females of the invasive fruit‐tree pinhole borer (an ambrosia beetle), Xyleborinus saxeseni(Ratzeburg), and an invasive bark beetle, Hypothenemus eruditusWestwood (both Coleoptera: Scolytidae), showed relatively higher flight responses than either sex of P. juglandisduring most assays, suggesting higher population densities of these two other invasive species at the two orchards or a greater sensitivity to host volatiles. Xyleborinus saxeseniand H. erudituspreferred to land on J. majorover J. californicaand on J. californicaover the negative control. Similarly, an invasive longhorned beetle, Nathrius brevipennis(Mulsant) (Coleoptera: Cerambycidae), showed a significant preference for J. majorover J. californica, but not for J. californicaover the negative control.

Citation

Lona, Irene D.; Miller, Donald G.; Hatfield, Colleen A.; Rosecrance, Richard C.; Nelson, Lori J.; Audley, Jackson P.; Siefker, Megan A.; Chen, Yigen; Seybold, Steven J. 2020. Host selection behavior mediated by differential landing rates of the walnut twig beetle, Pityophthorus juglandis, and associated subcortical insect species, on two western North American walnut species, Juglans californica and J. major. Entomologia Experimentalis et Applicata. 168(3): 240-258. https://doi.org/10.1111/eea.12883.