Caldwell Elizabeth, Read Jennifer, Sanson Gordon D
School of Biological Sciences, Monash University, Victoria 3800, Australia.
School of Biological Sciences, Monash University, Victoria 3800, Australia
Ann Bot. 2016 Feb;117(2):349-61. doi: 10.1093/aob/mcv178. Epub 2015 Dec 29.
There is abundant evidence that leaf mechanical traits deter feeding by insect herbivores, but little is known about which particular traits contribute to defence across feeding guilds. We investigated the contribution of multiple mechanical traits from shear, punch and tear tests to herbivore deterrence across feeding guilds.
Visible damage from miners and external chewers was measured and sucker feeding density estimated in mature leaves of 20 species of forest shrubs and small trees. Cafeteria trials were undertaken using a generalist chewer (larvae of Epiphyas postvittana, Lepidoptera). Damage was compared with leaf mechanical traits and associated nutrient and chemical defence traits.
Damage by external chewers in the field and by E. postvittana correlated negatively with mechanical traits. Hierarchical partitioning analysis indicated that the strongest independent contribution to chewing damage was by the material trait of specific work to shear, with 68 % of total variance explained by the combination of specific work to shear (alone explaining 54 %) and tannin activity in a regression model. Mining damage did not correlate with mechanical traits, probably because miners can avoid tissues that generate high strength and toughness in mature leaves. Mechanical traits correlated more strongly with chewing damage in the field than chemical defences (total phenolics and tannin activity) and nutrients (nitrogen and water), but nutrients correlated strongly with diet selection in the cafeteria trial. Surprisingly, sucker feeding density correlated positively with mechanical traits and negatively with nutrients.
Mechanical traits of mature leaves influenced insect feeding guilds differentially, reflecting differences in life history and feeding modes. For external chewers, energy (work) to fracture in shearing tests, at both structural and material levels, was strongly predictive of damage. Knowing which leaf mechanical traits influence insect feeding, and in which guilds, is important to our wider understanding of plant-herbivore interactions.
有充分证据表明叶片机械性状可阻止昆虫食草动物取食，但对于哪些特定性状有助于不同取食类群的防御作用，人们了解甚少。我们研究了剪切、冲压和撕裂试验中的多种机械性状对不同取食类群食草动物威慑作用的贡献。
测量了20种森林灌木和小树木成熟叶片上潜叶虫和外部咀嚼者造成的可见损伤，并估算了吸汁昆虫的取食密度。使用一种多食性咀嚼者（后黄卷蛾幼虫，鳞翅目）进行了自助餐试验。将损伤情况与叶片机械性状以及相关的营养和化学防御性状进行了比较。
野外外部咀嚼者和后黄卷蛾造成的损伤与机械性状呈负相关。层次划分分析表明，对咀嚼损伤的最强独立贡献来自于剪切比功这一材料性状，在一个回归模型中，剪切比功（单独解释了54%）和单宁活性的组合解释了总方差的68%。潜叶损伤与机械性状不相关，可能是因为潜叶虫可以避开成熟叶片中产生高强度和韧性的组织。在野外，机械性状与咀嚼损伤的相关性比化学防御（总酚和单宁活性）和营养物质（氮和水分）更强，但在自助餐试验中，营养物质与食物选择密切相关。令人惊讶的是，吸汁昆虫的取食密度与机械性状呈正相关，与营养物质呈负相关。
成熟叶片的机械性状对昆虫取食类群的影响存在差异，反映了生活史和取食方式的不同。对于外部咀嚼者，在结构和材料层面上，剪切试验中的断裂能量（功）能强烈预测损伤情况。了解哪些叶片机械性状影响昆虫取食以及影响哪些取食类群，对于我们更全面地理解植物 - 食草动物相互作用至关重要。
