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

Abstract

The host selection behaviour of the walnut twig beetle, Pityophthorus juglandis, was assessed by monitoring the landing rates of the beetles with sticky sheet traps on the host and nonhost hardwood branches. 2 Sticky sheet traps were deployed for 8 weeks from 6 June to 2 August. 2017 in the Putah Creek Riparian Reserve, Davis, CA. Branches from host northern California black walnut, Juglans hindsii, were paired with branches from six nonhost hardwood species. 3 The landing rate of P. juglandis (412 beetles trapped/8 weeks; 389 on host branches, 23 on nonhost branches) was significantly greater on the host branches for all nonhost hardwoods except Populus fremontii. Proportional comparisons of beetle presence also revealed a significant preference for the host branches compared with all but two nonhost species, Acer negundo and P. fremontii. 4 Capturing P. juglandis without the use of an aggregation pheromone was a rare event, underscoring the difficulty of studying the initial phases of host selection behaviour in bark beetles. Unbaited funnel traps adjacent to selected host trees in the experiment only captured five individuals over a 19-week period. None were captured in traps adjacent to nonhost trees. 5 This study provided evidence that P. juglandis discriminates between host and nonhost branches while in-flight. This directed flight behaviour is likely informed by the recognition of both host and nonhost volatile cues. 6 This study established an ecological context for the development of a semiochemical-based repellent system for protecting walnut trees from future attacks from this invasive bark beetle.

Walnut twig beetle landing rates differ between host and nonhost hardwood trees under the influence of aggregation pheromone in a northern California riparian forest

“…This indicates that Neuropterans may be present in high numbers throughout the Putah Creek Riparian Reserve. We also trapped a considerable number (53 specimens, Table 4) of Nathrius brevipennis , an invasive cerambycid, a finding that is consistent with other recent trapping studies (Audley et al ., 2020; Lona et al ., 2020). Additionally, we trapped two individuals of notable, relatively rare Coleoptera species, specifically Phymatodes vulneratus (Cerambycidae) and Trypophloeus thatcheri (Scolytidae), three Anobiidae species; Ptilinus sp., Petalium californicum , and Priobium punctatum .…”

“…Our study provides important context for the future management of thousand cankers disease. It provides field‐based evidence that WTB responds to long‐distance cues to identify and locate host trees during dispersal (Audley et al ., 2020). Additionally, it provides a foundation for future investigation of potentially repellent nonhost plant volatiles.…”

“…Audley et al . (2020) found the effect of the pheromone lure to have a fairly localized effect on WTB behaviour, influencing landing rates within 200 cm of the lure. Study trees were within 45 m of the north shore of Putah Creek along an east–west transect of approximately 2 km (Fig.…”

“…The host colonization behaviour of WTB may be explained by one of two prevailing hypotheses that explain bark beetle host colonization: (i) Walnut twig beetle may actively respond to long‐range volatile cues and signals while in flight to locate an appropriate host tree; (ii) WTB may be influenced by gustatory cues and shorter‐range olfactory signals/cues once it has landed on a tree to select host which indicates use of random landing (Raffa et al ., 2016). It has been shown that WTB likely uses long‐range signals and/or cues while in flight to select susceptible hosts (Hishinuma, 2017; Audley et al ., 2020; Lona et al ., 2020). While feeding, the male beetle releases an aggregation pheromone (3‐methyl‐2‐buten‐1‐ol) to attract female and additional male beetles to the tree (Seybold et al ., 2015).…”

Disruption of coniferophagous bark beetle (Coleoptera: Curculionidae: Scolytinae) mass attack using angiosperm nonhost volatiles: from concept to operational use

“…Brattli et al (1998) found that some bark beetle species were able to detect and differentiate between traps baited with host and nonhost material in flight in host, nonhost, and mixed (containing hosts and nonhosts) stands. Similarly, Audley et al (2020b) showed that Pityophthorus juglandis Blackman (Coleoptera: Curculionidae) can discriminate between hosts and nonhosts while in flight.…”