Sniffing out stress: Behavioral responses of Xylosandrus germanus to stressed apple trees

Xylosandrus germanus, commonly known as the black stem borer, is an invasive ambrosia beetle causing substantial damage in high-density apple orchards in the northeastern United States. Host selection by ambrosia beetles is influenced by volatile organic compounds (VOCs) emitted from stressed trees. However, limited research has examined beetle preference for specific abiotic and biotic stressors common in orchard systems. Additionally, VOC profiles are known to differ among stress types, potentially affecting beetle attraction. This study aims to investigate the behavioral response of the black stem borer to VOCs emitted from flood-stressed, drought-stressed, fire blight-infected, or healthy apple trees, and to characterize the VOC profiles associated with these stressors. A four-arm olfactometer assay with 25 responding female beetles was used, with each arm connected to a treatment (i.e., a stressed or non-stressed tree). Beetle choice was recorded over a 16-hour period, replicated ten times per treatment. Simultaneously, VOCs were collected from apple trees using Solid Phase Microextraction (SPME) fibers for analysis of the VOC profile. We hypothesized that beetles will exhibit preference for stressed trees relative to healthy controls, with distinct VOC profiles associated with each stressor, which could potentially be further exploited for field-based behavioral manipulation. Findings from this study will enhance understanding of ambrosia beetle host selection behavior and support integrated pest management strategies by identifying orchard stress conditions which increase vulnerability to attack and characterizing the specific volatile compounds involved.