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

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 AbstractThe walnut twig beetle, Pityophthorus juglandis Blackman (Coleoptera: Scolytidae), vectors a phytopathogenic fungus, Geosmithia morbida Kola r ık et al. (Hypocreales), which causes thousand cankers disease (TCD) in walnut (Juglans sp.) and wingnut (Pterocarya sp., both Juglandaceae) trees. We investigated an early point in disease inception in two walnut species -Juglans californica S. Wats. and Juglans major (Torr. ex Sitsgr.) Hellernative to riparian forests of the western USA by comparing P. juglandis flight and landing responses to small-diameter branch sections. Twenty unbaited branch sections (10 each of J. californica and J. major) were presented in a completely randomized design to populations of P. juglandis at the USDA Agricultural Research Service, National Clonal Germplasm Repository (NCGR) Juglans collection 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. juglandis flight 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. californica and J. major. Two additional assays (5 and 6) were completed at the NCGR to compare responses to branch sections of J. californica and 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. californica over J. major. In assay 5 there was no preference by males or females for J. californica over the negative control, perhaps due to the low flight activity-abundance of P. juglandis during the assay. When repeated at a time of higher flight activity-abundance (assay 6), male and female landing rates on J. californica exceeded 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 eruditus Westwood (both Coleoptera: Scolytidae), showed relatively higher flight responses than either sex of P. juglandis during most assays, suggesting higher population densities of these two other invasive species at the two orchards or a greater sensitivity to host volatiles. Xyleborinus saxeseni and H. eruditus preferred to land on J. major over J. californic...

A study of landing behaviour by the walnut twig beetle,Pityophthorus juglandis, among host and nonhost hardwood trees in a northern California riparian forest

“…The latter was true for host comparisons with all nonhosts pooled and for five of the six nonhosts individually. A future comparative test between landing on nonhost branches vs. non-emitting surrogate branches (Lona et al, 2020) would be interesting to pursue to further establish the role of nonhost repellency in this system.…”

“…A future comparative test between landing on nonhost branches vs . non‐emitting surrogate branches (Lona et al ., 2020) would be interesting to pursue to further establish the role of nonhost repellency in this system.…”

“…We reported eight other species of bark beetles or ambrosia besides P. juglandis , including the invasive ambrosia beetle Xyleborinus saxeseni , and the invasive bark beetle Hypothenemus eruditus (only females of both species were captured; males are flightless). We have trapped large numbers of both of these subcortical beetles in commercial walnut ( J. regia ) orchards in California (Seybold et al ., 2016; Lona et al ., 2020), but have had very few observations of their activity in association with native riparian black walnut. The large catch of X. saxeseni landing on live host branches is somewhat confusing as this species is known to prefer declining branches/trees (Seybold et al ., 2016).…”

“…The invasive cerambycid Nathrius brevipennis was encountered in relative abundance during the study (174 specimens, Table 4). This species has been observed landing on several species of walnut in large numbers (Seybold et al ., 2016; Hishinuma, 2017); however, it has typically been observed in commercial J. regia walnut orchards (Lona et al ., 2020). A close association of N. brevipennis with adventive J. regia in the USA is logical considering the Eurasian origin of both the beetle (Linsley, 1963) and the tree (Aradhya et al ., 2006).…”

“…5:1; Table 4) during our landing assays is consistent with similar sex ratios reported by Lona et al . (2020) on their landing traps from two orchard locations in California. Another interesting result was the apparent preference of both specimens from the Chrysoperla carnea species complex and Hemerobius sp.…”