Trap assays of the walnut twig beetle, Pityophthorus juglandis Blackman (Coleoptera: Curculionidae: Scolytinae), reveal an effective semiochemical repellent combination

Abstract

Thousand cankers disease (TCD), is an invasive insect-disease complex caused by the walnut twig beetle, Pityophthorus juglandis, and fungal pathogen, Geosmithia morbida. Semiochemical interruption is a viable option for protecting walnut trees from P. juglandisattack. The goal of this study was to test beetle responses to potential repellent compounds. The results of five, flight-intercept assays are reported. Assays 1–3 tested four compounds at variable release rates: (S)-(−)-verbenone, (R)-(+)-verbenone, racemic chalcogran, and racemic trans-conophthorin. Trapping results indicated that the highest release rate tested for each compound was the most effective in reducing the number of beetles caught. (S)-(−)-Verbenone was the least effective, reducing P. juglandistrap catches by 66%. (R)-(+)-Verbenone reduced the number of P. juglandisby 84%. Neither enantiomer of verbenone performed as well as chalcogran or trans-conophthorin, which both reduced the number of beetles caught by ca. 98%. Following individual assays, the most effective compounds were tested in subtractive-combination assays. Combinations of high release rates for (R)-(+)-verbenone, trans-conophthorin, and two stereoisomers of limonene (tested in a previous study) were tested in two assays. The subtractive-combination assays were inconclusive in that trap catches were similar across all treatments. All combination treatments were highly effective, achieving approximately 99% reduction in the number of beetles caught. Based on the trapping results, commercial availability, and cost of the semiochemicals tested, we conclude that a combination of (R)-(+)-limonene, trans-conophthorin, and (R)-(+)-verbenone constitutes an effective tool for reducing P. juglandistrap catches.

Citation

Audley, Jackson P.; Bostock, Richard M.; Seybold, Steven J. 2020. Trap assays of the walnut twig beetle, Pityophthorus juglandis Blackman (Coleoptera: Curculionidae: Scolytinae), reveal an effective semiochemical repellent combination. Journal of Chemical Ecology. 46(11-12): 1047-1058. https://doi.org/10.1007/s10886-020-01228-9.