Longitudinal study of Caribbean pine elucidates the role of 4-allylanisole in patterns of chemical resistance to bark beetle attack

Abstract

Southern pine beetles (Dendroctonus frontalis Zimmermann) and symbiotic fungi are associated with mass mortality in stands of Caribbean pine (Pinus caribaea Morelet). This study provides a 12.7-year assessment of semiochemical mediation between southern pine beetle and Caribbean pine in relation to concentrations of 4-allylanisole (estragole, methyl chavicol) and monoterpenes measured by gas chromatography–mass spectrometry in different seasons in premontane and coastal pine stands of Belize and Guatemala. Individual trees and stands with >2.5% (relative mass %) of 4-allylanisole in the xylem oleoresin exhibited significantly less beetle-induced mortality than those with <2.5%. Changes in relative levels of 4-allylanisole and monoterpenes during this study are consistent with seasonal temperature and cumulative water deficit effects and suggest bark beetle attack of P. caribaea may intensify in the future.

Toxicity of two Engelmann spruce (Pinaceae) monoterpene chemotypes from the southern Rocky Mountains to North American spruce beetle (Coleoptera: Scolytidae)

“…The current study shows that the concentration of monoterpene blends representing two widespread Engelmann spruce phloem chemotypes is likely to impact the probability of spruce beetle survival during initial colonisation of host trees. Moreover, the two Engelmann spruce chemotypes tested here differed in their relative toxicity to beetles, indicating that tree chemical composition also impacts spruce beetle survival (Raffa and Smalley 1995;Eidson et al 2017;Hammer et al 2020). However, this difference was small and eroded as monoterpene concentrations increased, and total mortality of beetles (100%) was observed over a 24-h period for both chemotypes when concentrations exceeded 100 μg/L.…”

4‐allylanisole as a lure adjuvant for Dendroctonus frontalis (Coleoptera: Curculionidae: Scolytinae) and two associated beetles

“…Furthermore, elevated levels of 4‐allylanisole are associated with lower D. frontalis ‐caused mortality of Pinus caribaea var. hondurensis Barrett & Golfari in Central America (Hammer et al, 2020; Snyder & Bower, 2005). However, P. taeda bred from parents that had escaped predation by D. frontalis within infestations had lower levels of 4‐allylanisole than trees in the general population (Strom et al, 2002).…”

Composition of Attractant Semiochemicals of North American Species of Dendroctonus Bark Beetles: A Review

“…The composition of resin constituents also may be an indicator of host condition or susceptibility. Elevated concentrations of the resin semiochemical 4-allylanisole were found to be associated with Pinus caribaea Morelet experiencing either higher [242] or lower [230] rates of mortality from D. frontalis, and individual pines treated to render them more susceptible to D. frontalis attack had depressed levels of this compound [243]. Lower levels of 4-allylanisole were also found in trees attacked by D. ponderosae [84].…”

“…Host compounds found to influence Dendroctonus attraction (Figure 2) have predominantly been the volatile constituents of host resin, including the monoterpenes alpha-pinene, beta-pinene, 3-carene, terpinolene, limonene, myrcene, and camphene; the phenylpropanoid 4-allylanisole; and n-heptane (produced by Jeffrey pine, Pinus jeffreyi Balf.). Typically, conifer resin contains a blend of volatile compounds, with compound identities and proportions having specific associations with tree species, population, and susceptibility to insect colonization [84,[228][229][230][231][232][233][234]. Ethanol is a general attractant for bark and ambrosia beetle species that require weakened hosts for reproduction [235][236][237][238], and of the three Dendroctonus species that respond to ethanol (D. valens, D. terebrans, and D. pseudotsugae) only the final is considered aggressive within its native range.…”