Faculty of Agriculture, Iwate University, Morioka, Japan.
Field Science Center for Northern Biosphere, Hokkaido University, Sapporo, Japan.
Environ Entomol. 2021 Apr 23;50(2):427-432. doi: 10.1093/ee/nvaa162.
Outbreaks of the gypsy moth (Lymantria dispar japonica Motschulsky) cause serious defoliation in birch. A single year of defoliation has no significant impact on the trees, whereas continuous defoliation events could be fatal. How birch species avoid serious damage caused by gypsy moth outbreak is yet to be revealed. Trichomes on leaf surfaces of birch trees are an effective antiherbivore defense strategy. We examined a 1-yr delayed induction of glandular (GT) and nonglandular trichomes (NGT) on leaf surfaces caused by stress in white birch (Betula platyphylla Sukaczev var. japonica [Miq.] Hara) and monarch birch (Betula maximowicziana Regel). Saplings were subjected to four treatments in June 2009: herbivory (50% of the leaf area was grazed by gypsy moths), mechanical cutting (50% of the leaf area was cut using scissors), shading (50% light shading with a black sheet), and control (covered with a net to prevent herbivory). Then, the density of GT and NGT on early leaves was determined in April 2010. In both birch species, the density of GT was higher in herbivory than in other treatments. The density of GT due to mechanical cutting was higher than that in the control, but only for white birch. However, the density of NGT was lower after mechanical cutting than in other treatments for white birch. There were no differences in the density of NGT among treatments for monarch birch. These results show that 1-yr delayed induction of GT by herbivory was stronger in white birch than in monarch birch.
舞毒蛾（Lymantria dispar japonica Motschulsky）的爆发会导致桦树严重落叶。一年的落叶对树木没有显著影响，而连续的落叶事件可能是致命的。桦树物种如何避免舞毒蛾爆发造成的严重损害尚不清楚。叶片表面的毛状体是桦树抵御食草动物的一种有效防御策略。我们研究了白桦（Betula platyphylla Sukaczev var. japonica [Miq.] Hara）和毛桦（Betula maximowicziana Regel）叶片表面的腺毛（GT）和非腺毛（NGT）在应激作用下 1 年的延迟诱导。2009 年 6 月，对幼树进行了 4 种处理：取食（用舞毒蛾取食叶片面积的 50%）、机械切割（用剪刀切割叶片面积的 50%）、遮荫（用黑幕布遮光 50%）和对照（用网覆盖防止取食）。然后，在 2010 年 4 月确定早期叶片上 GT 和 NGT 的密度。在两种桦树中，GT 的密度在取食处理下高于其他处理。机械切割引起的 GT 密度高于对照处理，但仅在白桦中如此。然而，机械切割后白桦的 NGT 密度低于其他处理。毛桦的 NGT 密度在不同处理之间没有差异。这些结果表明，与毛桦相比，白桦对取食诱导的 GT 延迟 1 年的诱导更强。
