USDA Forest Service, Pacific Southwest Research Station, 1731 Research Park Drive, Davis, CA, USA.
Department of Plant Pathology, University of California, Davis, CA, USA.
J Econ Entomol. 2021 Jun 11;114(3):1180-1188. doi: 10.1093/jee/toab054.
The walnut twig beetle, Pityophthorus juglandis Blackman, the vector of thousand cankers disease (TCD), poses a significant threat to North American walnut (Juglandaceae Juglans) trees. Despite discovery of TCD-related tree mortality over a decade ago, management options are lacking. This study represents the culmination of several years of investigating the chemical ecology of P. juglandis in hopes of developing a semiochemical repellent to disrupt the beetle's host colonization and aggregation behaviors. Numbers of P. juglandis landing on semiochemical-treated Juglans regia L. trees in a commercial walnut orchard were compared based on captures on sticky traps. Two repellent combinations were tested: R-(+)-limonene and trans-conophthorin (LimeCon), and R-(+)-limonene, trans-conophthorin, and R-(+)-verbenone (LCV). Both repellents reduced P. juglandis aggregation (captures) equally; thus, we proceeded with the LimeCon combination to reduce potential treatment cost. Subsequent trials included a 2× dose (Dual) of LimeCon. Both LimeCon and Dual significantly reduced the number of P. juglandis caught compared with the baited control, however, only for the lower of two trap positions. Beetle landings were modeled by trap distance from repellent placement on each tree. Beetle responses to the pheromone lure were surprisingly localized and did not bring the whole tree under attack. LimeCon, LCV, and Dual treatments averaged fewer than a single beetle caught for all trap distances; however, performance of the repellents beyond 150 cm is not clear due to the localized landing response of P. juglandis to pheromone lures. Further testing is required to fully analyze the zone of inhibition of the LimeCon repellent.
胡桃枝小蠹，Pityophthorus juglandis Blackman，是千疮百孔病（TCD）的载体，对北美胡桃（Juglandaceae Juglans）树构成了重大威胁。尽管十多年前就发现了与 TCD 相关的树木死亡，但仍缺乏管理措施。本研究代表了几年来对胡桃枝小蠹化学生态学研究的总结，希望开发出一种半化学驱避剂来破坏甲虫的宿主定殖和聚集行为。在一个商业胡桃果园里，根据粘性陷阱上的捕获情况，比较了在半化学处理过的 Juglans regia L.树上降落的胡桃枝小蠹数量。测试了两种驱避组合：（+）-柠檬烯和反-康朴桐素（LimeCon），以及（+）-柠檬烯、反-康朴桐素和（+）-马鞭草烯酮（LCV）。两种驱避剂都同样减少了胡桃枝小蠹的聚集（捕获）；因此，我们继续使用 LimeCon 组合来降低潜在的处理成本。随后的试验包括 2×剂量（双份）的 LimeCon。与诱饵对照相比，LimeCon 和 Dual 都显著减少了捕获的胡桃枝小蠹数量，但仅在两个诱捕器位置中的较低位置有效。根据每棵树上驱避剂放置位置与诱捕器的距离来模拟胡桃枝小蠹的降落。令人惊讶的是，胡桃枝小蠹对信息素诱饵的反应是局部的，并没有使整棵树受到攻击。LimeCon、LCV 和 Dual 处理的所有诱捕器距离平均捕获的胡桃枝小蠹少于一只；然而，由于胡桃枝小蠹对信息素诱饵的局部降落反应，LimeCon 驱避剂的抑制区域的性能尚不清楚。需要进一步的测试来全面分析 LimeCon 驱避剂的抑制区域。
