Effect of the western conifer seed bug <i>Leptoglossus occidentalis</i>, an invasive alien insect, on seed production reduction in Japanese black pine <i>Pinus thunbergii</i>

To determine the potential reduction of the seed productivity of Japanese black pine (<i>Pinus thunbergii</i>) by the western conifer seed bug (<i>Leptoglossus occidentalis</i>), two feeding experiments were conducted in the center of Kyushu Island, southwestern Japan, in fall of 2020. First, <i>L. occidentalis</i> individuals and a preharvested <i>P. thunbergii</i> cone were enclosed in a nonwoven fabric bag for 2 weeks, which yielded a mean filled seed rate of 18.8% compared with that of 35.6% in the control. Second, <i>L. occidentalis</i> individuals and harvested cones were enclosed in a plastic case for 1 week, affording a mean filled seed rate of 25.7% compared with that of 36.4% in the control. These results suggest that <i>L. occidentalis</i> feeding reduces the filled seed rate of <i>P. thunbergii</i> and damages the seed orchards of this species. Additionally, <i>P. thunbergii</i> seeds from cones damaged by <i>L. occidentalis</i> could be distinguished by their germination ability when sorted using an ethanol floatation technique. Overall, these findings suggest the importance of carefully monitoring <i>L. occidentali</i>s infestation in <i>P. thunbergii</i> seed orchards.

为探究西方针叶球果缘蝽（Leptoglossus occidentalis）对日本黑松（Pinus thunbergii）种子生产力的潜在抑制效应，2020年秋季于日本西南部九州岛中部开展了两项取食实验。其一，将西方针叶球果缘蝽个体与预采收的日本黑松球果封装于无纺布封袋中饲养2周，其饱实种子率均值为18.8%，而对照组饱实种子率为35.6%。其二，将西方针叶球果缘蝽个体与已采收的日本黑松球果放置于塑料盒中饲养1周，其饱实种子率均值为25.7%，对照组则为36.4%。上述结果表明，西方针叶球果缘蝽的取食行为会降低日本黑松的饱实种子率，对该树种的种子园造成危害。此外，采用乙醇浮选技术对受西方针叶球果缘蝽侵害的球果所产的日本黑松种子进行分选时，可通过其萌发能力区分受虫害与未受虫害的种子。综上，本研究结果凸显了对日本黑松种子园中的西方针叶球果缘蝽侵染情况开展精细化监测的重要性。