Dunn James P, Potter Daniel A, Kimmerer Thomas W
Department of Entomology, University of Kentucky, 40546-0091, Lexington, KY, USA.
Department of Forestry, University of Kentucky, 40546-0091, Lexington, KY, USA.
Oecologia. 1990 Jul;83(4):458-468. doi: 10.1007/BF00317195.
The twolined chestnut borer, Agrilus bilineatus (Weber) (Coleoptera: Buprestidae), attacks oaks (Quercus spp.) that have been weakened by prior environmental or biotic stress. Our earlier work showed that trees with relatively low winter starch reserves are more likely to be attacked by A. bilineatus the following summer. We hypothesized that such trees may have less energy available for defense (Callus formation and allelo-chemical synthesis) in tissues wounded by borer larvae. However, wounding experiments showed little or no relationship between winter or summer carbohydrate reserves, callus formation, radial growth, or concentrations of tannins and phenolics in wounded or nonwounded phloem tissues. Trees with relatively low winter carbohydrate reserves were again found to be attractive to adult A. bilineatus, although not all low starch trees were attacked or successfully colonized by borers. There was a trend for carpenterworm larvae, Prinoxystus robiniae (Lepidoptera: Cossidae), a generalist bark and wood borer, to be more successful in establishing galleries on low starch trees. Carpenterworms gained significantly more weight when fed phloem from trees attractive to A. bilineatus. Oaks that attracted large numbers of A. bilineatus or that were successfully colonized by the borer produced significantly less callus than did non-attacked trees when experimentally wounded at about the time of Agrilus egg hatch. Callus formation may limit the establishment of small larvae that feed slowly in the cambial region. These results indicate that current theory regarding relationships between increased tree stress and decreased allocation of energy reserves to radial growth and defense against phloem borers may be an oversimplification. We suggest that tree growth and the defensive response of phloem tissues may be limited more by the rate of carbohydrate utilization or by changes in source-sink relationships than by storage levels. Callus formation and synthesis of allelochemicals in wounded phloem may be under the same control as cambial activation, which is mediated by plant growth regulators and can be influenced by environmental conditions.
双线栗小蠹（Agrilus bilineatus (Weber)，鞘翅目：吉丁甲科）会攻击因先前环境或生物胁迫而衰弱的橡树（栎属）。我们早期的研究表明，冬季淀粉储备相对较低的树木在次年夏天更有可能受到双线栗小蠹的攻击。我们推测，这类树木在被小蠹幼虫咬伤的组织中用于防御（愈伤组织形成和化感物质合成）的能量可能较少。然而，创伤实验表明，冬季或夏季碳水化合物储备、愈伤组织形成、径向生长以及受伤或未受伤韧皮部组织中单宁和酚类物质的浓度之间几乎没有关系。再次发现，冬季碳水化合物储备相对较低的树木对双线栗小蠹成虫具有吸引力，尽管并非所有低淀粉含量的树木都会受到小蠹的攻击或成功被其定殖。对于多食性树皮和木材蛀虫——刺槐木蠹蛾（Prinoxystus robiniae，鳞翅目：木蠹蛾科）的幼虫而言，在低淀粉含量的树木上建立蛀道更有可能成功。当以对双线栗小蠹有吸引力的树木的韧皮部为食时，木蠹蛾幼虫体重显著增加。在双线栗小蠹卵孵化前后进行实验性创伤时，吸引大量双线栗小蠹或被小蠹成功定殖的橡树产生的愈伤组织明显少于未受攻击的树木。愈伤组织的形成可能会限制在形成层区域缓慢取食的小幼虫的定殖。这些结果表明，目前关于树木胁迫增加与能量储备分配减少之间关系的理论，以及能量储备分配减少对径向生长和抵御韧皮部蛀虫的影响，可能过于简单化。我们认为，树木生长和韧皮部组织的防御反应可能更多地受到碳水化合物利用速率或源 - 库关系变化的限制，而非储存水平的限制。受伤韧皮部中愈伤组织的形成和化感物质的合成可能与形成层的激活受相同的调控，而形成层的激活由植物生长调节剂介导，并且会受到环境条件的影响。
