The walnut twig beetle, Pityophthorus juglandis Blackman, and its associated fungal pathogen Geosmithia morbida—together known as thousand cankers disease (TCD)—threaten walnut trees (Juglans spp.) across North America and in Italy. Walnut is important both economically as timber and agricultural resources and ecologically as a key component in riparian forests. Despite the threat imposed by P. juglandis and TCD, effective management strategies are lacking. We sought to implement a chemical ecological approach to determine an effective semiochemical repellent tool. Potential compounds were initially screened in a series of trapping assays using multiple-unit funnel traps. R-(+)- and S-(–)-limonene released at ~700 mg/d, racemic trans-conophthorin released at 3 mg/d, and R-(+)-verbenone released at 50 mg/d were effective repellents individually and in combinations. Racemic chalcogran was also highly effective; however, limited commercial availability precluded further assessment. Based on trapping assay performance, we tested two combinations in an individual tree protection study: R-(+)-limonene + trans-conophthorin + R-(+)-verbenone (LCV); R-(+)-limonene + trans-conophthorin (LimeCon); and 2x dose of LimeCon. Repellent efficacy was measured by comparing numbers of P. juglandis caught on Stick-em® coated, clear acetate sheets placed at two locations on each study tree and on poles at two distances around a sub-set of study trees. Repellents significantly reduced the number of beetles landing on the treated trees; however, we could only confidently determine a zone of influence to 150 cm from the repellents. Experimental limitations and future research foci are discussed within the context of developing applied semiochemical management strategies.
