Dussourd David E
Department of Biology, University of Central Arkansas, Conway, Arkansas, United States of America.
PLoS One. 2015 Oct 30;10(10):e0141924. doi: 10.1371/journal.pone.0141924. eCollection 2015.
In North America, notodontid caterpillars feed almost exclusively on hardwood trees. One notable exception, Theroa zethus feeds instead on herbaceous plants in the Euphorbiaceae protected by laticifers. These elongate canals follow leaf veins and contain latex under pressure; rupture causes the immediate release of sticky poisonous exudate. T. zethus larvae deactivate the latex defense of poinsettia and other euphorbs by applying acid from their ventral eversible gland, thereby creating furrows in the veins. The acid secretion softens the veins allowing larvae to compress even large veins with their mandibles and to disrupt laticifers internally often without contacting latex. Acid secretion collected from caterpillars and applied to the vein surface sufficed to create a furrow and to reduce latex exudation distal to the furrow where T. zethus larvae invariably feed. Larvae with their ventral eversible gland blocked were unable to create furrows and suffered reduced growth on poinsettia. The ventral eversible gland in T. zethus and other notodontids ordinarily serves to deter predators; when threatened, larvae spray acid from the gland orifice located between the mouthparts and first pair of legs. To my knowledge, T. zethus is the first caterpillar found to use an antipredator gland for disabling plant defenses. The novel combination of acid application and vein constriction allows T. zethus to exploit its unusual latex-bearing hosts.
在北美，舟蛾科毛虫几乎只以阔叶树为食。一个显著的例外是泽舟蛾，它以大戟科的草本植物为食，这些植物受到乳汁管的保护。这些细长的管道沿着叶脉分布，内部含有处于压力之下的乳胶；管道破裂会导致粘性有毒分泌物立即释放。泽舟蛾幼虫通过从其腹部可外翻腺体分泌酸来解除一品红和其他大戟属植物的乳胶防御，从而在叶脉上形成沟槽。酸的分泌使叶脉变软，使幼虫能够用它们的下颚挤压甚至是粗大的叶脉，并常常在不接触乳胶的情况下从内部破坏乳汁管。从毛虫身上收集并涂抹在叶脉表面的酸足以形成一条沟槽，并减少沟槽远端的乳胶渗出，而泽舟蛾幼虫总是在这个部位取食。腹部可外翻腺体被堵塞的幼虫无法形成沟槽，并且在一品红上生长减缓。泽舟蛾和其他舟蛾科毛虫的腹部可外翻腺体通常用于威慑捕食者；受到威胁时，幼虫会从位于口器和第一对腿之间的腺体孔中喷出酸液。据我所知，泽舟蛾是第一种被发现利用用于解除植物防御的反捕食腺体的毛虫。酸的涂抹和叶脉收缩这一新颖的组合使泽舟蛾能够利用其不同寻常的含乳胶宿主。
