Brassicaceous plants are attacked by a wealth of specialist herbivores that include the Diamondback moth (DBM) Plutella xylostella L. (Lepidoptera: Plutellidae), control of which requires novel biocontrol strategies. DBM is a cosmopolitan pest causing damage that varies yearly in Finland depending on the timing and extent of their migration. Intercropping with companion plants can hamper host location by herbivores or attract their natural enemies. We tested two sustainable companion plant-based protection strategies on field-grown broccoli (Brassica oleracea var. italica), which comprised 1) aromatic and repellent-releasing Rhododendron tomentosum (RT) (bottom-up strategy), and 2) nectar-producing buckwheat Fagopyrum esculentum (FE) (top-down strategy) combined with an early-season floating row cover (mechanical control) (MC + FE). In addition, a control (no companion plant or cover) and mechanical control (MC) without FE were included. DBM adults on yellow sticky traps and larvae on plants were counted, and feeding damage on leaves was quantified. Volatile organic compounds emitted by broccoli plants in control and RT plots, and emitted by boundary RT plants in RT plots, were identified and quantified. There was a mass outbreak of DBM in early summer with a population peak in mid-July when the second adult generation emerged. DBM adult densities were significantly lower in RT and MC + FE than in control plots. Broccoli in RT plots had a lower larval density and lower damage intensity than in control plots in the early-season. Larval densities and damage intensities were the highest in the latter half of July. Control plots had the highest number of larvae followed by RT, MC, and MC + FE plots. Damage intensities in control plots were significantly higher than in all other treatments throughout the season. Damage intensity was lower in MC and MC + FE plots than in RT plots at the end-of-July. R. tomentosum emitted two characteristic sesquiterpene alcohols, palustrol and ledol, but no evidence of adsorption and re-release of these compounds from Brassica plants grown in RT plots was found. We conclude that incorporating RT as a boundary plant and using a mechanical row cover reduces DBM damage on broccoli, but further multi-year trials under varying degrees of pest pressure are needed.

十字花科植物受到大量专业食草动物的攻击，其中包括小菜蛾 (DBM) Plutella xylostella L.（鳞翅目：小菜蛾科），对此的控制需要新颖的生物防治策略。 DBM 是一种世界性害虫，在芬兰造成的损害每年有所不同，具体取决于其迁徙的时间和范围。与伴生植物间作可能会妨碍食草动物的寄主位置或吸引其天敌。我们对田间种植的西兰花（Brassica oleracea var. italica）测试了两种可持续的基于植物的保护策略，其中包括 1) 芳香且释放驱虫剂的绒毛杜鹃(RT)（自下而上策略），以及 2) 产生花蜜的策略荞麦Fagopyrum esculentum (FE)（自上而下策略）与早季浮行覆盖（机械控制）（MC + FE）相结合。此外，还包括没有 FE 的控制（无配套植物或覆盖物）和机械控制 (MC)。对黄色粘虫上的 DBM 成虫和植物上的幼虫进行了计数，并量化了对叶子的摄食损害。对对照和 RT 地块中西兰花植物排放的挥发性有机化合物以及 RT 地块中边界 RT 植物排放的挥发性有机化合物进行了鉴定和量化。 DBM在初夏大规模爆发，7月中旬出现种群高峰，第二代成虫出现。 RT 和 MC + FE 中的 DBM 成虫密度显着低于对照地块。早季时，RT 地块中的西兰花幼虫密度和损害强度均低于对照地块。幼虫密度和为害强度以7月下旬最高。对照区的幼虫数量最多，其次是 RT、MC 和 MC + FE 区。整个季节对照地块的损害强度明显高于所有其他处理。 7 月底，MC 和 MC + FE 地块的损伤强度低于 RT 地块。R. tomentosum释放出两种特征性的倍半萜醇：长青藤醇和 ledol，但没有发现 RT 地块中生长的芸苔属植物吸附和再释放这些化合物的证据。我们的结论是，将 RT 作为边界植物并使用机械行覆盖可以减少 DBM 对西兰花的损害，但需要在不同程度的害虫压力下进行进一步的多年试验。